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Discussion
Depending on your environment, your DNS implementation may require that you cre‐
ate secondary zones to allow for load balancing for busy DNS servers or remote sites
connected by slow links. In this situation, you want to allow zone transfers to occur
between your AD integrated DNS servers and your secondary servers, but you want to
restrict which hosts can initiate zone transfers with your AD integrated name servers.
Allowing anyone to initiate a zone transfer with your domain controllers could provide
an attacker with information for mapping out your network; it is therefore critical that
you limit which hosts can pull zone transfers from your servers.
If you are using only Active Directory−integrated zones, the Name Servers tab will be
automatically populated with a list of all name servers that are authoritative for the
selected zone, and this is the recommended choice when you have a large network with
many name servers deployed. If any of your name servers are using standard zone files,
however, you will need to populate this tab manually for any secondary name servers
you deploy.
Specifying a list of IP addresses for hosts that can initiate zone transfers may be more
secure since it is more specific, but this approach has the trade-off of creating the ad‐
ditional management overhead of keeping track of the IP addresses of all name servers
on your network, so you should follow this approach only if your network is small and
you have relatively few name servers deployed. Another disadvantage of this approach
is that if you forget to add some IP addresses of name servers to your list, zone infor‐
mation stored on those servers could become stale, causing name resolution to fail for
some of your clients. This could result in some of your users experiencing difficulties
in accessing network resources.
DNS is secured, by default, because in the case of file-based zones, it is configured to
allow zone transfers only with servers listed on the Name Servers tab of a zone. In the
case of Active Directory integrated zones, DNS is configured to disallow zone transfers
entirely—they generally aren’t needed in an Active Directory environment because the
data replicates through Active Directory replication.
See Also
“Understanding zones and zone transfer”
13.7. Configuring Forwarding
Problem
You want to configure forwarding to allow for name resolution outside of your corporate
network.
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Solution
Using a graphical user interface
1. Open the DNS Management snap-in (dnsmgmt.msc).
2. Connect to the DNS server you want to modify. In the left pane, right-click on DNS
and select Connect to DNS Server. Select “The following computer” and enter the
target server name. Click OK.
3. Right-click on the server and select Properties.
4. Click the Forwarders tab.
5. Click the Edit button.
6. Enter the IP address, or DNS name, of the destination DNS server.
7. Click OK twice.
Using a command-line interface
The following command sets the default forwarders. Replace <IPsOfForwarders> with
a space-separated list of IP addresses for the name servers to forward requests to:
> dnscmd <ServerName> /resetforwarders <IPsOfForwarders>
For example:
> dnscmd dns01 /resetforwarders 10.22.3.4 10.22.3.5
The following command configures the default forwarder timeout:
> dnscmd <ServerName> /config /forwardingtimeout <NumSeconds>
The following command configures the forwarder timeout for a specific domain:
> dnscmd <ServerName> /config <DomainName> /forwardertimeout <NumSeconds>
Using PowerShell
Set-DnsServerForwarder -IPAddress "<IPAddress>" -Timeout "<Value>"
Discussion
Name servers have long supported the notion of forwarders. Rather than sending all
unresolved queries to the root Internet name servers, you can use forwarders to send
queries to a specific server or set of servers, perhaps hosted by your ISP or by a partner
corporation. This allows you to better control the name resolution process on your
network.
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Using PowerShell
By using the –PassThru switch, you can see the object that you are working with and
the values of the properties.
See Also
MS KB 304491 (Conditional Forwarding in Windows Server 2003); MS KB 811118
(Support WebCast: Microsoft Windows Server 2003 DNS: Stub Zones and Conditional
Forwarding)
13.8. Configuring Conditional Forwarding
Problem
You want to configure forwarding for specific domain names.
Solution
Using a graphical user interface
1. Open the DNS Management snap-in (dnsmgmt.msc).
2. Connect to the DNS server that you want to modify. In the left pane, right-click on
DNS and select Connect to DNS Server. Select “The following computer” and enter
the target server name. Click OK.
3. Expand the DNS server and then right-click on Conditional Forwarders. Click New
Conditional Forwarder.
4. Enter the DNS name of the domain you wish to forward.
5. Enter the IP address or DNS name of the destination DNS server.
6. Choose whether to store the forwarder in Active Directory or to modify the query
timeout period, and then click OK.
Using a command-line interface
dnscmd <ServerName> /zoneadd <DomainName> /forwarder <IPsOfForwarders>
Using PowerShell
Add-DnsServerConditionalForwarderZone "<DomainName>" -MasterServers↵
"<IPAddress>" -ReplicationScope <Forest|Domain|Legacy|Custom>↵
-ForwarderTimeout "<Value>"
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Discussion
With conditional forwarding, you can forward unresolved queries for specific domains
to different name servers. The most common use of conditional forwarding is when
you have two or more noncontiguous namespaces. Consider, for example, a merger
between the adatum.com and othercorp.com corporations. Normally, for the name
servers of adatum.com to resolve queries for othercorp.com, the queries would have to
first be forwarded to the root Internet name servers. With conditional forwarding, you
can configure the adatum.com DNS servers so that all requests for othercorp.comshould
be sent directly to the othercorp.com name servers and all other unresolved queries
should be sent to the Internet, and vice versa. The trade-off for this feature is the addi‐
tional CPU processing that’s necessary to examine each query and forward it to the
appropriate server, rather than just funneling all unresolved queries to a single external
server.
13.9. Delegating Control of an Active Directory
Integrated Zone
Problem
You want to delegate control of managing the resource records in a zone.
Solution
Using a graphical user interface
1. Open the DNS Management snap-in (dnsmgmt.msc).
2. If an entry for the DNS server you want to connect to does not exist, right-click on
DNS in the left pane and select Connect to DNS Server. Select “This computer” or
“The following computer”, and then enter the server you want to connect to (if
applicable) and click OK.
3. Expand the server in the left pane and expand either Forward Lookup Zones or
Reverse Lookup Zones, depending on the type of zone.
4. Right-click on the name of the zone and select Properties.
5. Click on the Security tab.
6. Click the Add button.
7. Use the Object Picker to locate the user or group to which you want to delegate
control.
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8. Under Permissions, check the Full Control box.
9. Click OK.
Using a command-line interface
The following command grants full control over managing the resource records in an
AD integrated zone:
> dsacls dc=<ZoneName>,cn=MicrosoftDNS,<DomainOrAppPartitionDN>↵
/G<UserOrGroup>:GA
Using PowerShell
The following script delegates full control of an AD integrated DNS zone to a particular
user or group:
$Path = [ADSI]"LDAP://dc=<ZoneName>,cn=MicrosoftDNS,cn=System,↵
<DomainOrAppPartitionDN>"
$Group = New-Object System.Security.Principal.NTAccount("<UserorGroup>")
$IdentityReference = $Group.Translate↵
([System.Security.Principal.SecurityIdentifier])
$Perms = New-Object System.DirectoryServices.ActiveDirectoryAccessRule↵
($IdentityReference,"GenericAll","Allow")
$Path.psbase.ObjectSecurity.AddAccessRule($Perms)
$Path.psbase.commitchanges()
Discussion
By default, members of the DNSAdmins group have control over DNS server and zone
configuration. You can delegate control of individual AD integrated zones by modifying
permissions on the zone object in AD. The solutions show examples for how to grant
full control to an additional user or group over a particular zone.
See Also
MS KB 256643 (Unable to Prevent DNS Zone Administrator from Creating New Zones)
13.10. Creating and Deleting Resource Records
Problem
You want to create and delete resource records in a zone.
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Solution
Using a graphical user interface
1. Open the DNS Management snap-in (dnsmgmt.msc).
2. If an entry for the DNS server you want to connect to does not exist, right-click on
DNS in the left pane and select Connect to DNS Server. Select “This computer” or
“The following computer,” and then enter the server you want to connect to (if
applicable) and click OK.
3. If you want to add or delete a record in a forward zone, expand the Forward Lookup
Zone folder. If you want to add or delete a record for a reverse zone, expand the
Reverse Lookup Zone folder.
To create a resource record, do the following:
1. In the left pane, right-click the zone and select the option that corresponds to the
record type you want to create—for example, New Host (A).
2. Fill in all required fields.
3. Click OK.
To delete a resource record, do the following:
1. In the left pane, click on the zone the record is in.
2. In the right pane, right-click on the record you want to delete and select Delete.
3. Click Yes to confirm.
Using a command-line interface
To add a resource record, use the following command:
> dnscmd <DNSServerName> /recordadd <ZoneName> <NodeName> <RecordType> <RRData>
The following command adds an A record in the adatum.com zone:
> dnscmd dc1 /recordadd adatum.com Server01 A 192.168.52.2
To delete a resource record, use the following command:
> dnscmd <DNSServerName> /recorddelete <ZoneName> <NodeName> <RecordType>↵
<RRData>
The following command deletes an A record in the adatum.com zone:
> dnscmd dc1 /recorddelete adatum.com wins01 A 192.168.52.2
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Using PowerShell
There are several PowerShell cmdlets available to create resource records for DNS zones:
Add-DnsServerResourceRecord
This cmdlet adds an available resource record for a given zone.
Add-DnsServerResourceRecordA
This cmdlet adds an A type record for IPv4 hosts in a given zone.
Add-DnsServerResourceRecordAAAA
This cmdlet adds an AAAA type record for IPv6 hosts in a given zone.
Add-DnsServerResourceRecordCName
This cmdlet adds a CNAME type record for a given zone.
Add-DnsServerResourceRecordDnsKey
This cmdlet adds a DNS Key record for DNSSEC zones.
Add-DnsServerResourceRecordDS
This cmdlet creates a Delegation of Signing record for a signed zone file.
Add-DnsServerResourceRecordMX
This cmdlet creates an MX record for mail records in a given zone.
Add-DnsServerResourceRecordPtr
This cmdlet creates a PTR record for reverse DNS lookup.
The following will add an A record named Host01 that corresponds to the IP address
10.0.0.3, in the adatum.com zone:
Add-DnsServerResourceRecordA -Name "Host01" -IPv4Address "10.0.0.3"↵
-ZoneName "adatum.com"
The following will delete an A record named Host01, without prompting for confir‐
mation, from the adatum.com zone:
Remove-DnsServerResourceRecord -ZoneName "adatum.com" -Name "Host01"↵
-RRType "A" -Force
Discussion
Using a graphical user interface
The DNS Management snap-in is good for creating a small number of records, but if
you need to add or delete more than a couple of dozen, then we’d recommend writing
a PowerShell script to automate the process.
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Using a command-line interface
Adding A, CNAME, and PTR resource records is pretty straightforward in terms of the
data you must enter, but other record types, such as SRV, require quite a bit more data.
The help pages for /recordadd and /recorddelete display the required information
for each record type. For example, to add an SRV record using dnscmd, you need to
specify the priority, weight, port, and hostname of the record, as in the following
example:
> dnscmd /recordadd adatum.com dc1.adatum.com SRV _kerberos 50 100 88
See Also
MSDN: MicrosoftDNS_ResourceRecord
13.11. Querying Resource Records
Problem
You want to query resource records.
Solution
Using a graphical user interface
1. Open the DNS Management snap-in (dnsmgmt.msc).
2. If an entry for the DNS server you want to connect to does not exist, right-click on
DNS in the left pane and select Connect to DNS Server. Select “This computer” or
“The following computer.” and then enter the server you want to connect to (if
applicable) and click OK.
3. Expand the lookup zone folder and then select the zone you wish to filter.
4. Right-click the zone name and select View→Filter.
5. Enter the filter parameters and then click OK.
6. Right-click the zone name again and click Refresh.
Using a command-line interface
In the following command, replace <RecordType> with the type of resource record you
want to find (e.g., A, CNAME, SRV) and <RecordName> with the name or IP address of
the record to match:
> nslookup -type=<RecordType> <RecordName>
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Using PowerShell
Get-DnsServerResourceRecord -ZoneName "<ZoneName>" -RRType "A"
Discussion
Using a command-line interface
You can leave off the -type switch, and the command will find any A, PTR, and CNAME
records that match <RecordName>.
You can also run nslookup from interactive mode, which can be entered by typing
nslookup at a command prompt with no additional parameters, or you can switch back
and forth between query types by using the set q=ANY command to reset nslookup.
Interactive mode allows you to issue a series of queries with more efficiency because
you don’t have to type nslookup or wait for the initial connection to the DNS server.
See Also
MSDN: MicrosoftDNS_ResourceRecord; RFC 1035 (Domain Names—Implementa‐
tion and Specification); RFC 1700 (DNS Parameters)
13.12. Modifying the DNS Server Configuration
Problem
You want to modify the DNS server settings.
Solution
Using a graphical user interface
1. Open the DNS Management snap-in (dnsmgmt.msc).
2. If an entry for the DNS server you want to connect to does not exist, right-click on
DNS in the left pane and select Connect to DNS Server. Select “This computer” or
“The following computer”, and then enter the server you want to connect to (if
applicable) and click OK.
3. Right-click on the server and select Properties.
4. Edit the server settings from the tabs that are displayed.
5. Click OK to commit the changes after you complete your modifications.
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Using a command-line interface
With the following command, replace <Setting> with the name of the setting to modify
and <Value> with the value to set:
> dnscmd <DNSServerName> /config /<Setting> <Value>
The following command enables the EnableDnsSec setting on dns01:
> dnscmd dns01 /config /EnableDnsSec 1
The following command disables the NoTcp setting on the local host:
> dnscmd /config /NoTcp 0
The following command sets the DsPollingInterval setting to 60 on dns02:
> dnscmd dns02 /config /DsPollingInterval 60
For the complete list of settings, run dnscmd /config from the command line.
Using PowerShell
There are several Windows PowerShell cmdlets that you can use to set DNS properties.
To view a list of all available cmdlets that set DNS properties, use the following
command:
Get-Command *Set-Dns*
Discussion
The Microsoft DNS server supports a variety of settings to configure everything from
scavenging and forwarders to logging. With the DNS Management snap-in, the settings
are spread over several tabs in the Properties page. You can get a list of these settings by
simply running dnscmd /config from a command line.
See Also
MSDN: MicrosoftDNS_Server
13.13. Scavenging Old Resource Records
Problem
You want to scavenge old resource records. DNS scavenging is the process whereby
resource records are automatically removed if they are not updated after a period of
time. Typically, this applies only to resource records that were added via dynamic DNS
(DDNS), but you can also scavenge manually created static records. DNS scavenging is
a recommended practice so that your DNS zones are automatically kept clean of stale
resource records.
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Solution
The following solutions will show how to enable automatic scavenging on all AD inte‐
grated zones.
Using a graphical user interface
1. Open the DNS Management snap-in (dnsmgmt.msc).
2. If an entry for the DNS server you want to connect to does not exist, right-click on
DNS in the left pane and select Connect to DNS Server. Select “This computer” or
“The following computer”, and then enter the server you want to connect to (if
applicable) and click OK.
3. Click on the server, right-click on it, and select “Set Aging/Scavenging for all zones”.
4. Check the box beside “Scavenge stale resource records”.
5. Configure the No-Refresh and Refresh intervals as necessary, and click OK.
6. Check the box beside “Apply these settings to the existing Active Directoryintegrated zones” and click OK.
7. Right-click on the server again and select Properties.
8. Select the Advanced tab.
9. Check the box beside “Enable automatic scavenging of stale resource records”.
10. Configure the scavenging period as necessary.
11. Click OK.
Using a command-line interface
> dnscmd <DNSServerName> /config /ScavengingInterval <ScavengingMinutes>
> dnscmd <DNSServerName> /config /DefaultAgingState 1
> dnscmd <DNSServerName> /config /DefaultNoRefreshInterval <NoRefreshMinutes>
> dnscmd <DNSServerName> /config /DefaultRefreshInterval <RefreshMinutes>
> dnscmd <DNSServerName> /config ..AllZones /aging 1
Using PowerShell
Set-DnsServerScavenging -ScavengingState $True -RefreshInterval "<Value>"↵
-ScavengingInterval "<Value>"
Start-DnsServerScavenging -Force
Discussion
There are four settings that you need to be aware of before enabling scavenging. You
must use caution when enabling scavenging, because an incorrect configuration could
lead to resource records getting deleted by mistake.
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The first setting you have to configure is the scavenging interval. This is the interval in
which the DNS server will kick off the scavenging process. It is disabled by default so
that scavenging does not take place unless you enable this setting. The default value is
seven days.
The second setting is the default aging configuration setting for new zones. If you want
all new zones to be configured for scavenging, set this to 1.
The next two settings control how records get scavenged. The no-refresh interval de‐
termines how much time must pass before a dynamically updated record can be updated
again. This setting is necessary to reduce how often a DNS server has to update its
timestamp of the resource record. The default value is seven days. This means that after
a resource record has been dynamically updated, the server will not accept another
dynamic update for the same record for another seven days. However, if the IP address
or some other data for the record changes, the server will still accept the new informa‐
tion. Static records have a timestamp of 0 and will not get scavenged in an automated
scavenging process.
The refresh interval setting is the amount of time that must pass after the no-refresh
interval during which a client can update its record before it is considered old or stale.
The default value for this setting is also 168 hours (seven days). If you use the default
values, the combination of the no-refresh interval and refresh interval would mean that
a dynamically updated record would not be considered stale for up to 14 days after its
most recent update. Combine this with the default scavenging interval, and it could be
up to 21 days before a record is deleted if the record became stale immediately after the
last scavenge process completed: 7 days (no refresh) + 7 days (refresh) + up to 7 days
(scavenge process) = up to 21 days.
The solutions in this recipe show you how to configure these settings for all zones that
are hosted on a server; however, you can configure these settings for individual zones
as well. In the GUI solution, you would do this by accessing the Properties sheet of an
individual zone rather than the server node; in dnscmd, simply specify the zone name
after /aging, /scavenginginterval, /defaultagingstate, /defaultnorefreshin
terval, or /defaultrefreshinterval.
13.14. Clearing the DNS Cache
Problem
You want to clear the DNS cache. The DNS cache contains resource records that are
cached by the server or workstation for a period of time in memory so that repeated
requests for the same record can be returned immediately. There are two types of DNS
cache. One pertains to the cache on the Windows DNS client resolver (this can refer to
both server and workstation operating systems when they are requesting DNS
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information from a server), and the other refers to the cache used by the Microsoft DNS
server software.
Solution
To flush the client resolver cache, use the following command:
> ipconfig /flushdns
To flush the client resolver cache by using PowerShell, use the following cmdlet:
Clear-DnsClientCache
To flush the DNS server cache, use any of the following solutions.
Using a graphical user interface
1. Open the DNS Management snap-in (dnsmgmt.msc).
2. Right-click on DNS in the left pane and select Connect to DNS Server.
3. Enter the server you want to connect to and click Enter.
4. Right-click on the server and select Clear Cache.
Using a command-line interface
The following command will clear the cache on <DNSServerName>. You can leave out
the <DNSServerName> parameter to simply run the command against the local server:
> dnscmd <DNSServerName> /clearcache
Using PowerShell
Clear-DnsServerCache -Force
Discussion
The client resolver cache is populated whenever a DNS lookup is performed on a work‐
station or server (e.g., by visiting a website in Internet Explorer, a DNS lookup is per‐
formed and cached). It’s important to remember that this cache will store positive DNS
responses as well as negative ones. For example, if lost network connectivity causes DNS
queries for an external resource like a mail server to fail, those queries will continue to
fail until the cache refreshes: the queries have been negatively cached.
The second type of cache is in place on Microsoft DNS servers and on some third-party
DNS servers. It is a cache of all DNS requests that the server has made while processing
queries from various clients. You can view this cache by browsing the Cached Lookups
folder for a server in the DNS Management snap-in. This folder is not shown by default,
so you’ll need to select Advanced from the View menu.
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With both the client and server cache, records are removed from the cache after the
record’s TTL value expires. The TTL is used to age records so that clients and servers
will request an updated copy of the record at a later point in order to receive any changes
that may have occurred.
13.15. Verifying That a Domain Controller Can Register Its
Resource Records
Problem
You want to verify that DNS is configured correctly so that a domain controller can
register its resource records, which are needed for clients to be able to locate various
AD services.
Solution
Using a command-line interface
With the following dcdiag command, replace <DomainName> with the FQDN of the
domain that the domain controller is in. This command has to be run from the domain
controller you want to test, not from an administrative workstation:
> dcdiag /test:RegisterInDNS /DnsDomain:<DomainName>
Starting test: RegisterInDNS
DNS configuration is sufficient to allow this domain controller to↵
dynamically register the domain controller
Locator records in DNS.
The DNS configuration is sufficient to allow this computer to dynamically↵
register the A record corresponding to its DNS name.
Using PowerShell
Test-DnsServer "<IPAddress>"
Discussion
With the default setup, domain controllers attempt to dynamically register the resource
records necessary for them to be located by Active Directory clients and other domain
controllers. Domain controllers must have their resource records populated in DNS in
order to function, but it can be very tedious and error-prone to register all of the records
manually. This is why allowing the domain controllers to use DDNS to automatically
register and update their records can be much easier from a support standpoint.
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The dcdiag command provides a RegisterInDNS switch that allows you to test whether
the DC can register its records. In the solution, we showed the output if the domain
controller passes the test.
Here is the output if an error occurs:
Starting test: RegisterInDNS
This domain controller cannot register domain controller Locator DNS↵
records. This is because it cannot locate a DNS server authoritative for the↵
zone adatum.com. This is due to one of the following:
1. One or more DNS servers involved in the name resolution of the adatum.com↵
name are not responding or contain incorrect delegation of the DNS zones; or
2. The DNS server that this computer is configured with contains incorrect↵
root hints.
The list of such DNS servers might include the DNS servers with which this↵
computer is configured for name resolution and the DNS servers responsible↵
for the following zones: adatum.com
Verify the correctness of the specified domain name and contact your↵
network/DNS administrator to fix the problem.
You can also manually add the records specified in the↵
%systemroot%\system32\config\netlogon.dns file.
As you can see, the output of dcdiag offers some options for resolving the problem. The
information provided will also vary depending on the error encountered.
See Also
Recipe 13.17 for registering a domain controller’s resource records
13.16. Enabling DNS Server Debug Logging
Problem
You want to enable DNS debug logging to troubleshoot issues related to DNS queries
or updates.
Solution
Using a graphical user interface
1. From the Administrative Tools, Open the DNS Management snap-in
(dnsmgmt.msc).
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2. Connect to the DNS Server you want to modify. In the left pane, right-click on DNS
and select Connect to DNS Server. Select “The following computer” and enter the
target server name. Click OK.
3. Right-click on the server and select Properties.
4. Click on the Debug Logging tab.
5. Select what you want to log and the location of the logfile.
6. Click OK.
Using a command-line interface
Use the following four commands to enable debug logging. For the log level, you have
to add together the event codes you want logged and specify the result in hex. The
available event codes can be found in Table 13-3.
> dnscmd <ServerName> /Config /LogLevel <EventFlagSumInHex>
Use the following command to specify the location of the logfile:
> dnscmd <ServerName> /Config /LogFilePath <DirectoryAndFilePath>
Use the following command to log only entries that pertain to certain IP addresses:
> dnscmd <ServerName> /Config /LogIPFilterList <IPAddress1>[,<IPAddress2>...]
Use the following command to specify the maximum logfile size:
> dnscmd <ServerName> /Config /LogFileMaxSize <NumberOfBytesInHex>
Use the following command to disable debug logging:
> dnscmd <ServerName> /Config /LogLevel 0
Using PowerShell
Set-DnsServerDiagnostics -SaveLogsToPersistentStorage $True↵
-LogFilePath "<LogFilePath>"
Discussion
With the DNS Server debug log, you can record all DNS operations received and initi‐
ated by the server, including queries, updates, zone transfers, etc. If you need to trou‐
bleshoot a particular host, you can use the LogIPFilterList setting in dnscmd or the
WMI DNS Provider to restrict the log to operations performed only for or by that host.
The most important debug log setting is the log level. With the DNS snap-in, you can
select from a list of available options. The DNS snap-in provides an intuitive interface
for selecting the required options. Table 13-3 contains all of the event codes with their
hexadecimal and decimal values for the command-line options.
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Table 13-3. DNS debug logging event codes
Hexadecimal value Decimal value Descriptions
0x0 0 No logging. This is the default.
0x1 1 Query transactions.
0x10 16 Notifications transactions.
0x20 32 Update transactions.
0xFE 254 Nonquery transactions.
0x100 256 Question packets.
0x200 512 Answer packets.
0x1000 4096 Send packets.
0x2000 8192 Receive packets.
0x4000 16384 UDP packets.
0x8000 32768 TCP packets.
0xFFFF 65535 All packets.
0x10000 65536 AD write transactions.
0x20000 131072 AD update transactions.
0x1000000 16777216 Full packets.
0x80000000 2147483648 Write-through transactions.
DNS debug logging can come in handy if you want to look at the dynamic update
requests a particular DNS server is processing. For example, if a client or DHCP server
is attempting to dynamically register records, you can enable the Update Transactions
log category on the DNS server you think should be processing the updates. If you don’t
see any update transactions, this can indicate that another server is processing the dy‐
namic update requests.
Transactions are not immediately written to the debug logfile as they
occur. They are buffered and written to the file after a certain number
of requests are processed.
See Also
MSDN: MicrosoftDNS_Server
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13.17. Registering a Domain Controller’s Resource Records
Problem
You want to manually force registration of a domain controller’s resource records. This
may be necessary if you’ve made some configuration changes on your DNS servers to
allow your domain controllers to start dynamically registering resource records.
Solution
Using a command-line interface
> nltest /dsregdns /server:<DomainControllerName>
Discussion
With the nltest command, a /dsregdns switch allows you to force registration of the
domain-controller-specific resource records. You can also force reregistration of its re‐
source records by restarting the NetLogon service on the domain controller. The Net‐
Logon service automatically attempts to reregister a domain controller’s resource re‐
cords every hour, so if you can wait that long, you do not need to use nltest.
See Also
Recipe 13.15 for verifying whether a domain controller is registering its resource records
13.18. Deregistering a Domain Controller’s
Resource Records
Problem
You want to manually deregister a domain controller’s resource records.
Solution
Using a command-line interface
With the following nltest command, replace <DomainControllerName> with the FQDN
of the domain controller you want to deregister and <DomainDNSName> with the FQDN
of the domain of which the domain controller is a member:
> nltest /dsderegdns: <DomainControllerName> /dom:<DomainDNSName>
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Discussion
When a domain controller is demoted from a domain, it dynamically deregisters its
resource records. This is a nice feature of the demotion process because it means you
do not have to manually remove all of the resource records or wait for scavenging to
remove them. If, however, you have a domain controller that crashes and you do not
plan to bring it back online, you’ll need to remove the records manually or wait for the
scavenging process to take place.
You can use the DNS Management MMC snap-in and even the dnscmd.exe utility to
manually remove them one by one, or you can use nltest, as shown in the solution.
The /dsderegdns switch also has /DomGUID and /DsaGUID options if you want to delete
the records that are based on the domain GUID and DSA GUID, respectively. You need
to know the actual GUIDs of the domain and domain controller to use those switches,
so if you don’t have them handy, it would be easier to delete them using the DNS Man‐
agement MMC snap-in.
13.19. Preventing a Domain Controller from Dynamically
Registering All Resource Records
Problem
You want to prevent a domain controller from dynamically registering its resource re‐
cords using DDNS. If you manually register a domain controller’s resource records,
you’ll want to prevent those domain controllers from attempting to dynamically register
them. If you do not disable them from sending dynamic update requests, you may see
annoying error messages on your DNS servers that certain DDNS updates are failing.
Solution
Using a command-line interface
> reg add HKLM\System\CurrentControlSet\Services\Netlogon\Parameters /v↵
UseDynamicDNS /t REG_DWORD /d 0
The operation completed successfully.
> net stop netlogon
The Net Logon service is stopping.
The Net Logon service was stopped successfully.
> del %SystemRoot%\system32\config\netlogon.dnb
> net start netlogon
The Net Logon service is starting.......
The Net Logon service was started successfully.
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Using PowerShell
$strRegPath = "HKLM:\System\CurrentControlSet\Services\Netlogon\Parameters"
new-ItemProperty -path $strRegPath -name "UseDynamicDNS" -type DWORD
set-ItemProperty -path $strRegPath -name "UseDynamicDNS" -value "0"
Stop-Service netlogon
$strPath = join-path (get-content env:SystemRoot) system32\config\netlogon.dnb
Remove-Item $strPath
Start-Service netlogon
Discussion
By default, domain controllers attempt to dynamically register their Active Directory
−related resource records every hour via the NetLogon service. You can prevent a do‐
main controller from doing this by setting the UseDynamicDNS value to 0 under
HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Netlogon\Parameters.
After you set that value, you should stop the NetLogon service, remove the %SystemRoot
%\system32\config\netlogon.dnb file and then restart NetLogon. It is necessary to re‐
move the netlogon.dnb file because it maintains a cache of the resource records that are
dynamically updated. This file will get re-created when the NetLogon service restarts.
See Also
Recipe 13.20 for preventing certain resource records from being dynamically registered;
MS KB 198767 (How to Prevent Domain Controllers from Dynamically Registering
DNS Names)
13.20. Preventing a Domain Controller from Dynamically
Registering Certain Resource Records
Problem
You want to prevent a domain controller from dynamically registering certain resource
records. It is sometimes advantageous to prevent certain resource records from being
dynamically registered. For example, if you want to reduce the load on the PDC Emu‐
lator for a domain, you can prevent some of its SRV records from being published, which
would reduce the amount of client traffic the server receives.
Solution
Using a graphical user interface
1. Open the Group Policy Management snap-in (gpmc.msc).
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2. Create a GPO linked to the Domain Controllers OU, or else edit an existing GPO.
3. Select Computer Configuration→Policies→Administrative Templates→Sys‐
tem→Net Logon→DC Locator DNS Records.
4. Enable the “Specify DC Locator DNS records not registered by the DCs” setting,
and list one or more of the following record types that should not be registered:
• Dc
• DcAtSite
• DcByGuid
• Gc
• Gc
• GcAtSite
• GcIpAddress
• GenericGc
• Kdc
• Ldap
• LdapIpAddress
• Rfc1510Kdc
• Rfc1510Kpwd
• Rfc1510UdpKdc
• Rfc1510UdpKpwd
Using a command-line interface
This command will disable the Ldap, Gc, and GcIpAddress resource records from being
dynamically registered:
> reg add HKLM\System\CurrentControlSet\Services\Netlogon\Parameters↵
/v DnsAvoidRegisterRecords /t REG_MULTI_SZ /d Ldap\0Gc\0GcIpAddress
> net stop netlogon
> del %SystemRoot%\system32\config\netlogon.dnb
> net start netlogon
Using PowerShell
$strRegPath = "HKLM:\System\CurrentControlSet\Services\Netlogon\Parameters"
$arrValues = "Ldap", "Gc", "GcIpAddress"
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New-ItemProperty -Path $strRegPath -Name "DnsAvoidRegisterRecords" -Type↵
MultiString
Set-ItemProperty -Path $strRegPath -Name "DnsAvoidRegisterRecords" -Value↵
$arrValues
Stop-Service netlogon
$strPath = Join-Path (Get-Content env:SystemRoot) system32\config\netlogon.dnb
Remove-Item $strPath
Start-Service netlogon
Discussion
The procedure to disable registration of certain resource records is very similar to that
described in Recipe 13.19 for preventing all resource records from being dynamically
registered; however, in this case you need to create a value called DnsAvoidRegisterRe
cords under the HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Net
logon\Parameters key. The type for DnsAvoidRegisterRecords should be REG_MUL
TI_SZ, and the data should be a whitespace-separated list of mnemonics. Mnemonics
are used to represent various resource records that domain controllers register. The
complete list of mnemonics is included in Table 13-4.
You can also control these values using Group Policy, in Computer Con
figuration\Policies\Administrative Templates\System\Netlogon.
Table 13-4. Registry mnemonics for resource records
Registry mnemonic Resource record
type
Resource record name
LdapIpAddress A <DnsDomainName>
Ldap SRV _ldap._tcp.<DnsDomainName>
LdapAtSite SRV _ldap._tcp.<SiteName>._sites.<DnsDomainName>
Pdc SRV _ldap._tcp.pdc._msdcs.<DnsDomainName>
Gc SRV _ldap._tcp.gc._msdcs.<DnsForestName>
GcAtSite SRV _ldap._tcp.<SiteName>._sites.gc._msdcs.<DnsForest
Name>
DcByGuid SRV _ldap._tcp.<DomainGuid>.domains._msdcs.<DnsForest
Name>
GcIpAddress A _gc._msdcs.<DnsForestName>
DsaCname CNAME <DsaGuid>._msdcs.<DnsForestName>
Kdc SRV _kerberos._tcp.dc._msdcs.<DnsDomainName>
KdcAtSite SRV _kerberos._tcp.dc._msdcs.<SiteName>._sites. <DnsDo
mainName>
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Registry mnemonic Resource record
type
Resource record name
Dc SRV _ldap._tcp.dc._msdcs.<DnsDomainName>
DcAtSite SRV _ldap._tcp.<SiteName>._sites.dc._msdcs.<DnsDomain
Name>
Rfc1510Kdc SRV _kerberos._tcp.<DnsDomainName>
Rfc1510KdcAtSite SRV _kerberos._tcp.<SiteName>._sites.<DnsDomainName>
GenericGc SRV _gc._tcp.<DnsForestName>
GenericGcAtSite SRV _gc._tcp.<SiteName>._sites.<DnsForestName>
Rfc1510UdpKdc SRV _kerberos._udp.<DnsDomainName>
Rfc1510Kpwd SRV _kpasswd._tcp.<DnsDomainName>
Rfc1510UdpKpwd SRV _kpasswd._udp.<DnsDomainName>
If you configure DCs not to register these domain-wide SRV records, such as in a branch
office environment, your branch office clients will still fail over to DCs in your hub site
if their local DC becomes unavailable. Clients will continue to use the hub site DCs until
they are rebooted, even if the local DC comes back online. MS KB 939252 provides a
hotfix for Windows XP and Windows Server 2003 that will improve client failover be‐
havior in this scenario. In Windows operating systems since Windows XP, there is im‐
provement and built-in control available. See TechNet for more details.
See Also
Recipe 13.19 for preventing all resource records from being dynamically registered
13.21. Allowing Computers to Use a Domain Suffix That Is
Different from Their AD Domain
Problem
You want to allow computers to use a domain suffix that is different from their AD
domain.
Solution
Using a graphical user interface
1. Open ADSI Edit.
2. Connect to the domain you want to edit.
3. Right-click on the domainDNS object and select Properties.
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4. Edit the msDS-AllowedDNSSuffixes attribute and the DNS suffix you want to add.
5. Click OK.
Using a command-line interface
Create an LDIF file called add_dns_suffix.ldf with the following contents:
dn: <DomainDN>
changetype: modify
add: msDS-AllowedDNSSuffixes
msDS-AllowedDNSSuffixes: <DNSSuffix>
-
Then run the following command:
> ldifde -v -i -f add_dns_suffix.ldf.ldf
You can also make this change using AdMod, as follows:
> admod -b <DomainDN> msDS-AllowedDNSSuffixes:+:<DNSSuffix>
Using PowerShell
You can modify the list of allowed DNS suffixes for a domain using PowerShell, as
follows:
Set-ADObject "<DomainDN>" -Add @{"msDS-AllowedDNSSuffixes"="<Suffix>"}
Discussion
Windows Server and client domain members dynamically maintain the dNSHostName
and servicePrincipalName attributes of their corresponding computer object in Active
Directory with their current hostname. By default, those attributes can only contain
hostnames that have a DNS suffix equal to the Active Directory domain the computer
is a member of.
If the computer’s DNS suffix is not equal to the Active Directory domain, as may be the
case during a domain migration or a corporate merger or consolidation, 5788 and 5789
events will be generated in the System event log on the domain controllers the clients
attempt to update. These events report that the dnsHostName and servicePrincipal
Name attributes could not be updated due to an incorrect domain suffix. You can avoid
this by adding the computer’s DNS suffix to the msDS-AllowedDNSSuffixes attribute
on the domain object (e.g., dc=adatum,dc=com).
See Also
MS KB 258503 (DNS Registration Errors 5788 and 5789 When DNS Domain and Active
Directory Domain Name Differ)
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13.22. Authorizing a DHCP Server
Problem
You want to permit (i.e., authorize) a DHCP server to process DHCP requests from
clients. This is necessary only if the DHCP server is a member of an Active Directory
domain.
Solution
Using a graphical user interface
1. Open the DHCP snap-in (dhcpmgmt.msc).
2. If necessary, in the left pane, right-click on DHCP and select Add Server. Type in
the name of the DHCP server you want to target and click OK.
3. Click on the server entry in the left pane.
4. Right-click on the server and select Authorize.
If the DHCP server is not a member of an Active Directory domain,
you will not see the Authorize option.
Using a command-line interface
The following command authorizes a DHCP server in Active Directory:
> netsh dhcp add server <DHCPServerName> <DHCPServerIP>
This example shows how to authorize the DHCP server named dhcp01.adatum.com
with IP 192.168.191.15:
> netsh dhcp add server dhcp01.adatum.com 192.168.191.15
Using PowerShell
The following PowerShell command will authorize a DHCP server in Active Directory:
Add-DhcpServerInDC -DnsName "<ServerName>"
Discussion
Windows-based DHCP servers that belong to an Active Directory domain must be
authorized before they can give leases to clients. This feature helps reduce the danger
of a rogue Windows DHCP server that an end user sets up, perhaps even unintentionally.
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However, this still doesn’t prevent someone from plugging in a non-Windows DHCP
server (e.g., a Linksys router with the DHCP server enabled) and causing clients to
receive bad leases. A rogue DHCP server can provide incorrect lease information or
deny lease requests altogether, ultimately causing a denial of service for clients on your
network.
A DHCP server that is a member server of an Active Directory domain performs a query
in Active Directory to determine whether it is authorized. If it is, it will respond to
DHCP requests; if not, it will not respond to requests.
A standalone Windows DHCP server that is not a member of an Active Directory do‐
main sends out a DHCPINFORM message when it first initializes. If an authorized
DHCP server responds to the message, the standalone server will not respond to any
further DHCP requests. If it does not receive a response from a DHCP server, it will
respond to client requests and distribute leases.
DHCP servers are represented in Active Directory as objects of the dhcpClass class, in
the cn=NetServices,cn=Services,cn=Configuration,<ForestRootDN> container.
The relative distinguished name of these objects is the IP address of the DHCP server.
There is also an object in the same container named cn=dhcpRoot, which is created after
the first DHCP server is authorized. It has an attribute named dhcpServers that contains
all authorized servers. By default, only members of the Enterprise Admins group can
authorize DHCP servers. However, you can delegate the rights to authorize a DHCP
server. Do the following to delegate the necessary permissions to a group called DHCP
Admins:
1. Open ADSI Edit from the Support Tools while logged on as a member of the
Enterprise Admins group.
2. In the left pane, expand the Configuration Container→cn=Configura
tion→cn=Services→cn=NetServices.
3. Right-click on cn=NetServices and select Properties.
4. Select the Security tab.
5. Click the Advanced button.
6. Click the Add button.
7. Use the object picker to select the DHCP Admins group.
8. Check the boxes under “Create dHCPClass objects” and “Delete dHCPClass
objects.”
9. Click OK until all dialog boxes are closed.
10. Back in ADSI Edit, right-click on cn=dhcpRoot (if you’ve previously authorized
DHCP servers) and select Properties.
11. Select the Security tab.
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12. Click the Advanced button.
13. Click the Add button.
14. Use the object picker to select the DHCP Administrators group.
15. Check the boxes under Allow for Write All Properties.
16. Click OK until all dialog boxes are closed.
If the DHCP Administrators group does not exist, run the following
command on a DHCP server or on a computer with the DHCP man‐
agement tool installed:
netsh dhcp add securitygroups
Using a graphical user interface
You can quickly determine whether a DHCP server has been authorized by looking at
its server node in the left pane of the DHCP snap-in. If the icon has a little red flag, it
isn’t authorized; if the flag is green, it is authorized.
Using a command-line interface
To see the list of authorized servers using the command line, run the following
command:
> netsh dhcp show server
Using PowerShell
Get-DhcpServerInDC
See Also
“Controlling DHCP Active Directory Authorization”
13.23. Restricting DHCP Administrators
Problem
You want to restrict who can administer your DHCP servers in your domain.
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Solution
Using a graphical user interface
1. Open the Active Directory Users and Computers MMC snap-in (dsa.msc).
2. In the console tree, click Active Directory Users and Computers→<Domain
Name>→Users.
3. In the Details pane, click DHCP Administrators.
If the DHCP Administrators group does not exist, run the following
command:
netsh dhcp add securitygroups
4. Click Action→Properties→Members.
5. Remove all users and groups you do not want to have administering your DHCP
server by clicking their names and then clicking Remove.
6. To add new DHCP administrators, click Add, provide the user or group name, and
then click OK.
7. Click OK.
Using a command-line interface
Add a member to a group with DSMod by passing the -addmbr option:
> dsmod group "<GroupDN>" -addmbr "<MemberDN>"
To add a group member with AdMod, use the following syntax:
> admod -b "<GroupDN>" member:+:"<MemberDN>"
Remove a member from a group with DSMod by passing the -rmmbr option:
> dsmod group "<GroupDN>" -rmmbr "<MemberDN>"
To remove a group member with AdMod, use the following syntax:
> admod -b "<GroupDN>" member:-:"<MemberDN>"
Replace the complete membership list with DSMod by passing the -chmbr option:
> dsmod group "<GroupDN>" -chmbr "<Member1DN Member2DN ...>"
To replace the membership of a group with AdMod, use the following command:
> admod -b "<GroupDN>" member:+-:"<Member1DN>;<Member2DN>;<Member3DN>"
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Using PowerShell
You can add a user or group to the membership of the DHCP Administrators group
using the Add-ADGroupMember command as follows:
Add-ADGroupMember "DHCP Administrators" "<User/Group>"
Discussion
In Active Directory, most roles can be assigned independently of one another rather
than just by making a user a Domain Admin or an Enterprise Admin. This is great for
security administrators who want to ensure that users have only enough rights to per‐
form their assigned tasks. For example, a user Fred might need to modify an enterprisewide object. You could just add Fred to the Enterprise Admin groups to solve the prob‐
lem. However, Fred now has access to virtually any object in the entire forest and could
cause irreparable harm to your network, not to mention compromising all security in
place. Instead, you can grant Fred access to just that object.
This can be done in different ways. One method is to use the Delegation of Control
Wizard. Another way is to use the several built-in groups in Windows that are created
and populated when specific services are installed. One such group is DHCP Adminis‐
trators, which is created when the first DHCP server is brought up in a domain. You
can control administrative access to the DHCP function of these servers through this
group membership.
Nondomain joined computers also have a DHCP Administrators group.
This is a local group on each computer and must be managed separately
on each server.
See Also
“DHCP Groups”
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CHAPTER 14
Security and Authentication
14.0. Introduction
The default Windows 2000 installation of Active Directory was not as secure as it could
have been out of the box. It allowed anonymous queries to be executed, which could
take up valuable processing resources, and it did not place any requirements on en‐
crypting or signing traffic between clients and domain controllers. As a result, user‐
names, passwords, and search results could be sent over the network in clear text. For‐
tunately, beginning with Windows Server 2003, things tightened up significantly. LDAP
traffic is signed by default, and anonymous queries are disabled by default. Additionally,
Transport Layer Security (TLS), the more flexible cousin of Secure Sockets Layer (SSL),
is supported, allowing for end-to-end encryption of traffic between domain controllers
and clients.
Active Directory’s ACL model provides ultimate flexibility for securing objects through‐
out a forest; you can restrict access down to the attribute level if you need to. With this
flexibility comes increased complexity. An object’s ACL is initially generated from the
default ACL for the object’s class, inherited permissions, and permissions directly ap‐
plied on the object.
An ACL is a collection of ACEs, which defines the permission and properties that a
security principal can use on the object to which the ACL is applied. Defining these
entries and populating the ACL is the foundation of Active Directory security and del‐
egation.
In this chapter, we will explore some of the common tasks of managing permissions in
Active Directory. If you are looking for a detailed guide to Active Directory permissions,
we suggest reading Active Directory, Fifth Edition, by Brian Desmond et al. (O’Reilly).
In order for ACLs to be of use, a user must first authenticate to Active Directory. Kerberos
is the primary network authentication system used by Active Directory. Kerberos is a
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standards-based system originally developed at MIT that has been widely implemented
at universities. We will also be covering some Kerberos-related tasks in this chapter that
you will likely encounter in an Active Directory environment. For a complete review of
Kerberos, we recommend Kerberos: The Definitive Guide by Jason Garman (O’Reilly).
14.1. Enabling SSL/TLS
Problem
You want to enable SSL/TLS access to your domain controllers so that clients can encrypt
LDAP traffic to the servers.
Solution
Using a graphical user interface (solution specific to Windows Server 2012)
1. Open Server Manager.
2. Click Manage, then click Add Roles and Features, and then click Next.
3. Click Next, which will select a role-based or featured-based installation.
4. Click Next to select the local server as the destination server.
5. Check the box beside Active Directory Certificate Services and then click Next.
6. The Add Roles and Features Wizard will appear. Maintain the option to include the
management tools, and then click the Add Features button to add the required
features to the role installation. Click Next.
7. On the features screen, click Next.
8. On the AD CS screen, click Next.
9. On the Role services screen, click Next.
10. Review the installation options and then click Install to begin the installation.
11. Upon completion of the installation, click Close.
12. Go back to Server Manager and click the notifications. In the Post-deployment
Configuration notification for AD CS, click the “Configure Active Directory Cer‐
tificate Services on the destination server” link.
13. On the Credentials screen, enter administrative credentials if needed and then click
Next.
14. On the Role Services screen, click Certification Authority and then click Next.
15. Select the setup type that you want and click Next.
16. Select the CA type that you want the server to be and click Next.
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17. The “Specify the type of the private key” screen appears. Click Next to create a new
private key.
18. The Cryptography for CA screen will appear. Click Next.
19. On the CA Name screen, click Next.
20. On the Validity Period screen, click Next.
21. Enter the location for the certificate database and logs, and then click Next.
22. Click Configure and then click Close when the installation completes.
Discussion
The GUI solution example installs AD CS on an existing domain controller. (While this
works, it is a good practice to separate AD DS and AD CS to separate servers when
possible.) Because the example installs AD CS on a domain controller, the domain con‐
troller automatically acquires a certificate after the installation is complete. If you install
AD CS on member server(s), you will need to acquire a certificate for each domain
controller. One way to do this is to create an auto-enrollment GPO for all domain con‐
trollers. After Active Directory domain controllers obtain certificates, they automati‐
cally listen on ports 636 and 3269. Port 636 is for LDAP over SSL/TLS and port 3269 is
used for global catalog queries performed over SSL/TLS. See Recipe 14.2 for more in‐
formation on how to query a domain controller using SSL/TLS.
See Also
“How to Enable Secure Socket Layer [SSL] Communication over LDAP for Windows
2000 Domain Controllers”; “How to enable LDAP over SSL with a third-party certifi‐
cation authority”
14.2. Securing LDAP Traffic with SSL, TLS, or Signing
Problem
You want to secure LDAP traffic using SSL, TLS, or signing.
Solution
Using a graphical user interface
Most of the GUI-based tools running on both client computers and server computers
will automatically sign and encrypt traffic between the server and client. This includes
the following tools:
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• Active Directory Domains and Trusts
• Active Directory Sites and Services
• Active Directory Schema
• Active Directory Users and Computers
• Active Directory Administrative Center
• ADSI Edit
• Group Policy Management snap-in
• Object Picker
With ADSI Edit, you can also specify the port number to use when browsing a partition.
View the settings for a connection by right-clicking on the partition and selecting Set‐
tings. Click the Advanced button and enter 636 for LDAP over SSL or 3269 for the global
catalog over SSL.
Using a command-line interface
The DS command-line tools support LDAP signing and encryption. This includes
DSAdd, DSMod, DSrm, DSMove, DSGet, and DSQuery. The joeware utilities also sup‐
port connecting using SSL security.
Discussion
It is a good idea to test whether traffic is being encrypted. If you run Network Monitor
(netmon.exe) while using tools that perform simple LDAP binds, you’ll see LDAP re‐
quests, usernames, and passwords going over the network in plain text. Obviously this
is not the most secure configuration. If you use some of the tools listed in the preceding
section, you will notice that you aren’t able to see the requests, usernames, or passwords.
Don’t take encryption for granted.
See Also
Recipe 14.1 for enabling SSL/TLS; Recipe 14.3; MSDN: ADS_AUTHENTICA‐
TION_ENUM
14.3. Disabling LDAP Signing
Problem
You want to disable LDAP signing.
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Solution
Using a graphical user interface
To temporarily disable LDAP encryption or signing for troubleshooting purposes, use
the following steps on a client computer:
1. Create a new GPO. Edit the GPO and select Computer Configuration→Poli‐
cies→Windows Settings→Security Settings→Local Policies, and then highlight Se‐
curity Options.
2. In the right pane, double-click the policy titled “Network security: LDAP client
signing requirements”.
3. Click the checkbox to define the policy setting and then select None as the setting.
4. Click OK.
5. Link the GPO to the container that contains the desired computer object(s).
Discussion
If the target domain controllers require signing, then disabling the client signing will
result in the client administrative tools not being able to communicate with the domain
controllers. To disable LDAP signing on domain controllers, follow the preceding steps
but modify the policy titled “Domain controller: LDAP server signing requirements”
in the Default Domain Controllers policy.
See Also
Recipe 14.2 to enable LDAP signing and encryption
14.4. Enabling Anonymous LDAP Access
Problem
You want to enable anonymous LDAP access for clients. Anonymous queries are dis‐
abled by default except for querying the RootDSE.
Solution
Using a graphical user interface
1. Open ADSI Edit.
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2. In the Configuration partition, browse to cn=Services→cn=Windows NT→cn=Di
rectory Service.
3. In the left pane, right-click on the Directory Service object and select Properties.
4. Double-click on the dSHeuristics attribute.
5. If the attribute is empty, set it with the value 0000002.
6. If the attribute has an existing value, make sure the seventh digit is set to 2.
7. Click OK twice.
Using PowerShell
$root = [ADSI]"LDAP://RootDSE"
$obj = [ADSI]("LDAP://cn=Directory Service,cn=Windows NT,cn=Services," +↵
$root.configurationNamingContext)
$dsHeuristics = $obj.dsHeuristics.value
if ($dsHeuristics -eq $null)
{
"dsHeuristics was null (not previously set)"
$dsHeuristics = "0000000" # seven zeroes
}
$len = $dsHeuristics.Length
if ($len -lt 7)
{
$dsHeuristics = $dsHeuristics + ("0000000").SubString(0, (7 - $len))
$len = 7
}
# we've ensured that $dsHeuristics is AT LEAST seven chars long now
# it may be 13 chars or more. we really don't care about that!
$char = $dsHeuristics.SubString(6, 1)
if ($char -eq "2")
{
"Anonymous query mode already set to 2"
}
else
{
$upd = $dsHeuristics.SubString(0, 6) + "2"
if ($dsHeuristics.Length -gt 7)
{
$dsHeuristics.SubString(7, $len)
}
$obj.dsHeuristics = $upd
$obj.SetInfo()
"Anonymous query mode set to 2"
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"New value of dsHeuristics equal to $upd"
}
Discussion
To enable anonymous access, you have to modify the dSHeuristics attribute of the
cn=Directory Service,cn=Windows NT,cn=Services,ConfigurationDN object. The
dSHeuristics attribute is an interesting attribute used to control certain behavior in
Active Directory. For example, you can enable List Object Access mode (see
Recipe 14.17) by setting the dSHeuristics flag.
The dSHeuristics attribute consists of a series of digits that, when set, enable certain
functionality. To enable anonymous access, the seventh digit must be set to 2. By default,
dSHeuristics does not have a value. If you set it to enable anonymous access, the value
would be 0000002.
After enabling anonymous access, the assumption is that you’ll want to grant access for
anonymous users to retrieve certain data from Active Directory. To do that, grant the
ANONYMOUS LOGON user access to the parts of the directory you want anonymous users
to search. You must grant the access from the root of the directory down to the object
of interest. See MS KB 320528 for an example of how to enable the anonymous user to
query the email addresses of user objects.
See Also
Recipe 14.17; “How to configure Active Directory to allow anonymous queries”; MSDN:
DS-Heuristics attribute
14.5. Using the Delegation of Control Wizard
Problem
You want to delegate control over objects in Active Directory to a user or group.
Solution
Using a graphical user interface
1. Open the Active Directory Users and Computers snap-in (dsa.msc) or Active Di‐
rectory Sites and Services snap-in (dssite.msc), depending on the type of object you
want to delegate.
2. In the left pane, browse to the object on which you want to delegate control.
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3. Right-click on the object and select Delegate Control. Only certain objects support
the Delegation of Control Wizard, so this option will not show up for every type of
object.
4. Click Next.
5. Click the Add button and use the object picker to select the users or groups to which
you want to delegate control.
6. Click Next.
7. If the task you want to delegate is an option under “Delegate the following common
tasks,” place a checkmark next to it and click Next. If the task is not present, select
“Create a custom task to delegate” and click Next. If you selected the latter option,
you will need to perform four additional steps:
a. Select the object type you want to delegate.
b. Click Next.
c. Select the permissions you want to delegate.
d. Click Next.
8. Click Finish.
Using a command-line interface
To grant permissions from the command line, use the following syntax:
> dsacls <ObjectDN> /g <Permissions>
For example, the following syntax will delegate the permission to read and write infor‐
mation to the description property:
> dsacls <ObjectDN> /g RPWP;description;
Discussion
The Delegation of Control Wizard is Microsoft’s attempt to ease the pain of trying to
set permissions for common tasks. Because Active Directory permissions are so gran‐
ular, they can also be cumbersome to configure. The Delegation of Control Wizard helps
in this regard, but it is still limited in functionality. The default tasks that can be delegated
are fairly minimal, although you can add more tasks as described in Recipe 14.6. Another
limitation is that you can only add new permissions; you cannot undo or remove per‐
missions that you previously set with the wizard. To do that, you have to use the ACL
Editor directly as described in Recipe 14.8.
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See Also
Recipe 14.6 for customizing the Delegation of Control Wizard; Recipe 14.7 for more on
using dsrevoke
14.6. Customizing the Delegation of Control Wizard
Problem
You want to add or remove new delegation options in the Delegation of Control Wizard.
Solution
Open the Delegation of Control Wizard INF file (%SystemRoot%\System32\Dele
gwiz.inf in Windows Server 2008 and later) on the computer for which you want to
modify the wizard.
Under the [DelegationTemplates] section, you’ll see a line similar to the following:
Templates = template1, template2, template3, template4, template5, template6,
template7, template8, template9,template10, template11, template12, template13
You need to append a new template name. In this case, we’ll follow the same naming
convention and create a template named template14. The line should now look like
this:
Templates = template1, template2, template3, template4, template5, template6,
template7, template8, template9,template10, template11, template12, template13,
template14
Scroll to the end of the file and append a new template section. You can use the other
template sections as examples. Here is the generic format:
[<TemplateName>]
AppliesToClasses = <CommaSeparatedListOfObjectClassesInvokedFrom>
Description = "<DescriptionShownInWizard>"
ObjectTypes = <CommaSeparatedListOfObjectClassesThatAreSet>
[<TemplateName>.SCOPE]<Permission entries for Scope>
[<TemplateName>.<ObjectClass1>]<Permission entries for ObjectClass1>
[<TemplateName>.<ObjectClass2>]<Permission entries for ObjectClass2>
...
<TemplateName> is the same as what we used in the [DelegationTemplates] section—
that is, template14.
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In the AppliesToClasses line, replace <CommaSeparatedListOfObjectClassesInvo
kedFrom> with a comma-separated list of LDAP display names of the classes that can
be delegated. This delegation action will show up on the classes listed here only when
you select Delegate Control from a snap-in. To make our new template entry apply to
domain objects, OUs, and containers, we would use this line:
AppliesToClasses = domainDNS,organizationalUnit,container
In the Description line, replace <DescriptionShownInWizard> with the text you want
shown in the wizard that describes the permissions being delegated. Here is a sample
description for delegating full control over inetOrgPerson objects:
Description = "Create, delete, and manage user and inetOrgPerson accounts"
In the ObjectTypes line, replace <CommaSeparatedListOfObjectClassesThatAre
Set> with a comma-separated list of object classes to be delegated. In this example,
permissions will be modified for user and inetOrgPerson objects:
ObjectTypes = user,inetOrgPerson
Next, define the actual permissions to set when this action is selected. You can define
two different types of permissions. You can use a [<TemplateName>.SCOPE] section to
define permissions that are set on the object that is used to start the wizard. This will be
one of the object classes defined in the AppliesToClass line. This is commonly used in
the context of containers and organizational units to specify, create, modify, or delete
child objects of a particular type. For example, to allow the granting of create (CC) or
delete (DC) permissions for user and inetOrgPerson objects, you would use the fol‐
lowing:
[template14.SCOPE]
user=CC,DC
inetOrgPerson=CC,DC
As you can see, each permission (e.g., create child) is abbreviated to a two-letter code
(e.g., CC). Table 14-1 lists the valid codes.
Table 14-1. Permissions and abbreviated codes
Abbreviated code Permission
RP Read Property
WP Write Property
CC Create Child
DC Delete Child
GA Full Control
It is perfectly valid to leave out a SCOPE section if it is not needed. The rest of the lines
are used to specify permissions that should be set on the object classes defined by the
ObjectTypes line.
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To allow the granting of full control over all existing user and inetOrgPerson objects,
we’ll use these entries:
[template14.user]
@=GA
[template14.inetOrgPerson]
@=GA
This is very similar to the previous example, except that here SCOPE is replaced with the
names of the object classes the permissions apply to. The @ symbol is used to indicate
that the permission applies to all attributes on the object. You can get more granular by
replacing @ with the name of the attribute the permission applies to. For example, this
would allow the granting of read and write permissions on the department attribute for
inetOrgPerson objects:
[template14.inetOrgPerson]
department=RP,WP
You can also enable control access rights using the CONTROLRIGHT designator instead of
@ or an attribute name; you just need to specify the LDAP display name of the control
access right you want to enable. The following section enables the Reset Password right
on inetOrgPerson objects and enables read and write access to the pwdLastSet
attribute:
[template14.inetOrgPerson]
CONTROLRIGHT="Reset Password"
pwdLastSet=RP,WP
Discussion
You can completely customize the tasks that can be delegated with the Delegation of
Control Wizard, but you still have the problem of getting the Delegwiz.inf file, on all the
clients that need to use the new settings. You can manually copy it to the computers that
need it, or you can use Group Policy to automate the distribution of it.
Microsoft offers a prebuilt delegation file that allows you to delegate more than 70
administrative tasks. The file can be used to replace the existing Delegwiz.inf file or it
can be used as a starting point if you only wanted to use a subset of the file. See the file
at TechNet for more information.
See Also
Recipe 14.5 for more on using the Delegation of Control Wizard
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14.7. Revoking Delegated Permissions
Problem
You want to remove permissions that you’ve delegated to a domain or an OU.
Solution
Using a graphical user interface
1. Open the Active Directory Users and Computers MMC snap-in (dsa.msc). Rightclick on the object that you wish to modify and select Properties.
2. From the Security tab, highlight the permissions entry that you wish to revoke and
click Remove, and then click OK.
Using a command-line interface
The following command will remove any permissions that have been delegated directly
to the ADATUM\jsmith user over the Finance Organizational Unit:
> dsrevoke /remove "/root:ou=Finance,dc=adatum,dc=com" ADATUM\jsmith
Discussion
While the Delegation of Control Wizard makes it trivial to grant permissions to objects
within Active Directory, one thing that it lacks is an Undo button. To help address this,
Microsoft has made the dsrevoke command-line utility a free download from its web‐
site. Note that the tool is dated as it was created originally for Windows 2000. It has been
a bit spotty on Windows Server 2008 and Windows Server 2008 R2, but we’ve used it
successfully with Windows Server 2012. The dsrevoke utility will remove any permis‐
sions that have been delegated to a security principal on a domain or an OU, with the
following limitations:
• You can use dsrevoke only on a domain or an OU; if you’ve delegated permissions
over individual objects, you’ll need to remove them manually.
• dsrevoke removes only object permissions; if you’ve assigned any user rights
through Group Policy, they’ll need to be removed separately.
• You can’t use dsrevoke to remove any permissions that have been delegated to the
Schema or Configuration NCs.
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See Also
“Best Practices for Delegating Active Directory Administration”
14.8. Viewing the ACL for an Object
Problem
You want to view the ACL for an object.
Solution
Using a graphical user interface
1. Open the ACL Editor. You can do this by viewing the properties of an object (rightclick on the object and select Properties) with a tool such as ADUC or ADSI Edit.
Select the Security tab. To see the Security tab with ADUC, you must select
View→Advanced Features from the menu.
2. Click the Advanced button to view a list of the individual ACEs.
Using a command-line interface
> dsacls <ObjectDN>
Using PowerShell
(Get-Acl "ad:\<ObjectDN>").Access | FL
Discussion
Viewing an object’s ACL is a common task and should already be familiar to most
administrators. The ACL Editor is useful for checking the permissions that have been
set on objects, especially after running the Delegation of Control Wizard. In addition
to viewing permissions, the options available in the GUI include viewing auditing set‐
tings and the owner of the object. Knowing the owner of an object is important because
ownership confers certain inherent rights.
Because the ACL Editor is the same for NTFS permissions and properties as it is for
Active Directory objects, you should feel comfortable with the look and feel of the
interface; it is exactly the same as file and folder permissions. We also highly recommend
getting familiar with the Advanced view of the ACL Editor, as this is truly the view in
which you can determine what is going on with permissions. The Basic view presents
a list of security principals that have permissions configured, but it will not always show
every configured ACE entry. The Advanced view will show the complete picture,
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including the scope of permissions for ACEs down to the object and even the attribute
level.
See Also
Recipe 14.12 for changing an ACL; Recipe 15.13 for auditing of object access
14.9. Customizing the ACL Editor
Problem
You want to set permissions on attributes that do not show up in the default Active
Directory Users and Computers ACL Editor.
Solution
The ACL Editor in ADUC and in the Active Directory Administrative Center shows
only a subset of the object’s attributes on which permissions can be set. Most attributes
can be seen in the ACL Editor by clicking the Advanced button, adding or editing a
permission entry, and selecting the Properties tab.
An attribute can have a read permission, a write permission, or both, either of which
can be set to Allow or Deny. If the attribute you want to secure is not in the list, you will
need to modify the dssec.dat file on the computer that you’re running the ACL Editor
from. On Windows Server 2012, the dssec.dat file is located in the %SYSTEMROOT%
\System32 folder.
There are sections for each object class represented in square brackets—for example,
[user]. Underneath that heading is a list of attributes that you can configure to display
or not display in the ACL Editor.
These are the first few lines for the [user] section:
[user]
aCSPolicyName=7
adminCount=7
allowedAttributes=7
The value to the right of the attribute determines whether it is shown in the ACL Editor.
The valid values include the following:
0
Both the Read property and the Write property are displayed for the attribute.
1
The Write property is displayed for the attribute.
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2
The Read property is displayed for the attribute.
7
No entries are displayed for the attribute.
If the attribute is not defined, then the default value (specified by @, if present) is
used.
Discussion
Much like the Delegation of Control Wizard, you can customize the attributes that are
shown in the ACL Editor, but you still need to distribute the dssec.datfile to all computers
that need to see the change.
After making the changes to dssec.dat, close ADUC and/or the Active Directory Ad‐
ministrative Center and then reopen them.
See Also
MS KB 296490 (How to Modify the Filtered Properties of an Object); MS KB 294952
(How to Delegate the Unlock Account Right)
14.10. Viewing the Effective Permissions on an Object
Problem
You want to view the effective permissions that a user or group has for a particular
object.
Solution
Using a graphical user interface (solution specific to Windows Server 2012)
1. Open the ACL Editor. You can do this by viewing the properties of an object (rightclick on the object and select Properties) with a tool such as ADUC or ADSI Edit.
Select the Security tab. To see the Security tab with ADUC, you must select
View→Advanced Features from the menu.
2. Click the Advanced button.
3. Select the Effective Access tab.
4. Click the “Select a user” button to bring up the Object Editor.
5. Find the user or group for which you want to see the effective permissions.
6. Click the “View effective access” button.
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The results will be shown in the bottom of the window.
The Effective Access tab is the new name for the Effective Permissions
tab since Windows Server 2008.
Using a command-line interface
> acldiag <ObjectDN> /geteffective:<UserOrGroupDN>
Discussion
Viewing the permissions on an object does not tell the whole story as to what the actual
translated permissions are for a user or group on that object. The effective permissions
of an object take into account all group membership and any inherited permissions that
might have been applied farther up the tree. While this is a useful tool to analyze per‐
missions, it is unfortunately only a best guess; there are still some situations in which
certain permissions will not be reflected.
The AclDiag tool is from the Windows Server 2003 Service Pack 2 32-bit Support Tools.
It is a free download, and it installs and works successfully up to Windows Server 2012.
See Also
AclDiag overview
14.11. Configuring Permission Inheritance
Problem
You want to configure permission inheritance on an Active Directory container to con‐
figure whether a child object should automatically receive any permissions that you’ve
granted to its parent object.
Solution
1. Open the ACL Editor. You can do this by viewing the properties of an object (rightclick on the object and select Properties) with a tool such as Active Directory Users
and Computers (ADUC) or ADSI Edit. Select the Security tab. If the Security tab
is not visible within ADUC, you must select View→Advanced Features from the
menu.
2. Click the Advanced button to view a list of the individual ACEs.
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3. To turn off inheritance, click the “Disable inheritance” button.
4. You will be given the option to “Convert inherited permissions into explicit per‐
missions on this object”, to “Remove all inherited permissions from this object”, or
to cancel. Click the desired option.
5. To reenable permission inheritance from objects farther up the directory structure,
click the “Enable inheritance” button in the Advanced Permissions window.
Using a command-line interface
To disable permission inheritance (i.e., to configure an object such that only explicitly
assigned permissions apply), use the following syntax:
> dsacls <ObjectDN> /P:Y
To enable permission inheritance, do the following:
> dsacls <ObjectDN> /P:N
Using PowerShell
The following syntax will prevent an object from receiving inherited permissions that
have been applied at a higher level in the tree:
$acl = Get-Acl -Path "AD:<ObjectDN>"
$acl.SetAccessRuleProtection($true,$true);Set-Acl -AclObject $acl "AD:<ObjectDN>"
The following syntax will configure an AD object so that it will receive inherited per‐
missions that have been applied at a higher level in the directory tree:
$acl = Get-Acl -Path "AD:<ObjectDN>"
$acl.SetAccessRuleProtection($false,$false);Set-Acl -AclObject $acl↵
"AD:<ObjectDN>"
Discussion
Similar to NTFS permissions on the filesystem, Active Directory permissions on con‐
tainer objects can be set to inherit or trickle down to objects farther down the directory
structure. This process can greatly simplify assigning permissions, as you can assign a
common set of permissions high up in the directory structure and have those permis‐
sions filter down to all of the OUs and objects below. In some cases, though, you might
want to turn off permission inheritance to configure an entirely different set of per‐
missions for a child object or container.
One thing to keep in mind when enabling or disabling inheritance is that there are a
number of AD security principals protected by the AdminSDHolder process that will
receive a specific set of permissions regardless of the inheritance settings you configure.
These groups include Enterprise Admins, Schema Admins, Domain Admins, Adminis‐
trators, Account Operators, Server Operators, Print Operators, Backup Operators, and
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Cert Publishers. In addition, some Active Directory−aware applications depend on in‐
heritance being in place in order to function efficiently.
See Also
“AdminSDHolder—or where did my permissions go?”; “Description and Update of the
Active Directory AdminSDHolder Object”
14.12. Changing the ACL of an Object
Problem
You want to change the ACL on an object to grant or restrict access to it for a user or
group.
Solution
Using a graphical user interface
1. Open the ACL Editor. You can do this by viewing the properties of an object (rightclick on the object and select Properties) with a tool such as ADUC, Active Directory
Administrative Center, or ADSI Edit. Select the Security tab. To see the Security tab
with ADUC, you must select Views→Advanced Features from the menu.
2. Click the Advanced button to view a list of the individual ACEs.
3. Click Add to specify a new user or group, and then place checkmarks next to the
permissions that you want to assign and click OK.
4. To remove an ACE, highlight the entry and click Remove. If the Permissions entry
is inherited from farther up the directory tree, the option to remove the permission
will not be available unless you disable inheritance. With inheritance enabled, you
will only have the option to remove any permissions that have not been inherited.
Using a command-line interface
To grant permissions from the command line, use the following syntax:
> dsacls <ObjectDN> /g <Permissions>
To deny permissions, replace /g with /d.
Using PowerShell
To add an entry for Full Control to the ACL of an object, use the following syntax:
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$Path = [ADSI]"LDAP://<ObjectDN>"
$Group = New-Object System.Security.Principal.NTAccount("<GroupName>")
$IdentityReference = $Group.Translate↵
([System.Security.Principal.SecurityIdentifier])
$Perms = New-Object System.DirectoryServices.ActiveDirectoryAccessRule↵
($IdentityReference,"GenericAll","Allow")
$Path.psbase.ObjectSecurity.AddAccessRule($Perms)
$Path.psbase.commitchanges()
Discussion
Changing the ACL of an object is a common task for administrators in any but the most
basic AD implementations because, as shown in Recipe 14.5 and Recipe 14.6, the Del‐
egation of Control Wizard is limited and cumbersome to extend and deploy. The GUI
and command-line methods are useful for one-off changes to permissions, but for
making global changes to a number of objects, you should consider using a script to
automate the process.
See Also
Recipe 7.10; Recipe 8.2; Recipe 13.9; Recipe 14.5; Recipe 14.6; Recipe 17.9
14.13. Changing the Default ACL for an Object Class
in the Schema
Problem
You want to change the default ACL for an object class in the schema.
Solution
Using a graphical user interface
1. Open the Active Directory Schema snap-in.
2. In the left pane, browse to the class you want to modify.
3. Right-click on it and select Properties.
4. Select the Default Security tab.
5. Use the ACL Editor to change the ACL.
6. Click OK.
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Discussion
Each instantiated object in Active Directory has an associated structural class that de‐
fines a default security descriptor (the defaultSecurityDescriptor attribute). When
an object is created and a security descriptor isn’t specified, the default security de‐
scriptor is applied to it. This, along with inheritable permissions from the parent con‐
tainer, determines how an object’s security descriptor is initially defined. If you find that
you are modifying the default security descriptor on a particular type of object every
time it is created, you may want to modify its default security descriptor. Another option
would be to use a script that would modify the individual object’s ACL at the same time
that the object was created.
See Also
Recipe 10.1 for more on registering the Active Directory Schema snap-in; Recipe 14.14
for comparing the ACL of an object to the default defined in the schema; Recipe 14.15
for resetting the ACL of an object to the default defined in the schema
14.14. Comparing the ACL of an Object to the Default
Defined in the Schema
Problem
You want to determine whether an object has the permissions defined in the schema
for its object class as part of its ACL.
Solution
Using a command-line interface
> acldiag <ObjectDN> /schema
Discussion
For more on the default security descriptor (SD), see Recipe 14.13. AclDiag will deter‐
mine whether the object possesses the security descriptor that’s defined in the schema
—if you’ve modified the security descriptor, AclDiag will compare the object’s SD against
the currently defined SD, not the Active Directory default.
See Also
Recipe 14.15 for resetting an object’s ACL to the default defined in the schema
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14.15. Resetting an Object’s ACL to the Default Defined in
the Schema
Problem
You want to reset an object’s ACL to the one defined in the schema for the object’s object
class.
Solution
Using a graphical user interface
1. Open the ACL Editor. You can do this by viewing the properties of an object (rightclick on the object and select Properties) with a tool such as ADUC, Active Directory
Administrative Center, or ADSI Edit. Select the Security tab. To see the Security tab
with ADUC, you must select View→Advanced Features from the menu.
2. Click the Advanced button.
3. Click the “Restore defaults” button.
4. Click OK twice.
Using a command-line interface
> dsacls <ObjectDN> /S
The /S parameter is case-sensitive.
Discussion
For more on the default security descriptor, see Recipe 14.13.
14.16. Enabling Strong Domain Authentication
Problem
You want to ensure that users can only authenticate to Active Directory using strong
authentication protocols.
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Solution
Using a graphical user interface
1. Open the Group Policy Management snap-in (gpmc.msc).
2. In the left pane, expand the Forest container, expand the Domains container, browse
to the domain you want to administer, and expand the Group Policy Objects
container.
3. Right-click on the GPO that controls the configuration of your domain controllers
and select Edit. (By default, this is the Default Domain Controller Policy, but it may
be a different GPO in your environment.) This will bring up the Group Policy Object
Editor.
4. Browse to Computer Configuration→Policies→Windows Settings→Security Set‐
tings→Local Policies→Security Options.
5. Double-click on “Network security: LAN Manager Authentication Level”. Place a
checkmark next to “Define this policy setting”.
6. Select “Send NTLMv2 response only. Refuse LM & NTLM.” Click OK.
7. Wait for Group Policy to refresh, or run the gpupdate /force command from the
command prompt.
Discussion
Microsoft operating systems have supported different flavors of LM and NT LAN Man‐
ager (NTLM) authentication since the earliest days of Windows. LM authentication is
an extremely old and weak authentication protocol that should no longer be used in
production environments unless absolutely necessary. By default, Windows 2000 Active
Directory supported client authentication attempts using LM, NTLM, or NTLMv2;
Windows Server 2003 and later support only NTLM and NTLMv2 out of the box.
The strongest NTLM authentication scheme you can select is to refuse LM and NTLM
authentication from any client, and to respond only to clients using NTLMv2. Depend‐
ing on your client configuration, though, enabling this option may require changes on
the client side as well. You can apply the same setting to a GPO linked to your Active
Directory domain to ensure that all of your clients will use NTLMv2 instead of older,
weaker protocols.
Windows Server 2008, Windows Server 2008 R2, and Windows Server 2012 Active
Directory have a default value of “Send NTLMv2 response only” for this GPO setting.
This is more secure than previous versions of the operating system but still allows do‐
main controllers to accept weaker authentication methods.
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See Also
“Introducing the Restriction of NTLM Authentication”; “Purging Old NT Security Pro‐
tocols”
14.17. Enabling List Object Access Mode
Problem
You want to prevent any authenticated user from being able to browse the contents of
Active Directory by default. Enabling List Object Access mode means that users will
need explicit permissions to see directory listings of containers.
Solution
Using a graphical user interface
1. Open ADSI Edit.
2. In the Configuration partition, browse to cn=Services→cn=Windows NT→cn=Di
rectory Service.
3. In the left pane, right-click on the Directory Service object and select Properties.
4. Double-click on the dSHeuristics attribute.
5. If the attribute is empty, set it with the value 001. If the attribute has an existing
value, make sure the third digit (from the left) is set to 1.
6. Click OK twice.
Using VBScript
On Error Resume Next ' necessary if dsHeuristics is not
' already set
' This code enables or disables list object mode for a forest.
' ------ SCRIPT CONFIGURATION -----
boolEnableListObject = 1 ' e.g. 1 to enable, 0 to disable
' ------ END CONFIGURATION --------
set objRootDSE = GetObject("LDAP://RootDSE")
set objDS = GetObject( _
"LDAP://cn=Directory Service,cn=Windows NT,cn=Services," ↵
& objRootDSE.Get("configurationNamingContext") )
strDSH = objDS.Get("dSHeuristics")
if len(strDSH) = 1 then
strDSH = strDSH & "0"
end if
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strNewDSH = Left(strDSH,2) & boolEnableListObject
if len(strDSH) > 3 then
strNewDSH = strNewDSH & Right(strDSH, len(strDSH) - 3)
end if
WScript.Echo "Old value: " & strDSH
WScript.Echo "New value: " & strNewDSH
if strDSH <> strNewDSH then
objDS.Put "dSHeuristics", strNewDSH
objDS.SetInfo
WScript.Echo "Successfully set list object mode to " & ↵
boolEnableListObject
else
WScript.Echo "List object mode already set to " & boolEnableListObject
end if
Discussion
List Object Access mode is useful if you want your users to view only a subset of objects
when doing a directory listing of a particular container, or you do not want them to be
able to list the objects in a container at all. This mode was originally intended for mul‐
titenant environments and should undergo thorough testing in an environment before
deploying to production. By default, the Authenticated Users group is granted the List
Contents access control right over objects in a domain. If you remove or deny this right
on a container by modifying the ACL, users will not be able to get a listing of the objects
in that container using tools such as ADUC or ADSI Edit.
To limit the objects that users can see when they pull up an object listing, you first need
to enable List Object Access mode as described in the solution. You should then remove
the List Contents access control right on the target container. Lastly, you’ll need to grant
the List Object right to the objects that the users or groups should be able to list.
Enabling List Object Access mode can significantly increase the administration over‐
head for configuring ACLs in Active Directory. It can also impact performance on a
domain controller since it will take considerably more time to verify ACLs before re‐
turning information to a client.
Using VBScript
This script requires the On Error Resume Next command in order to function. Without
this line in place, the script will throw an error if the dsHeuristics attribute is not set.
See Also
Ask the Directory Services Team blog
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14.18. Modifying the ACL on Administrator Accounts
Problem
You want to modify the ACL for user accounts that are members of one of the admin‐
istrative groups.
Solution
Using one of the methods described in Recipe 14.12, modify the ACL on the cn=Ad
minSDHolder,cn=Systems,<DomainDN> object in the domain that the administrator ac‐
counts reside in. The ACL on this object gets applied every hour to all user accounts
that are members of the administrative groups.
Discussion
If you’ve ever tried to directly modify the ACL on a user account that was a member of
one of the administrative groups in Active Directory, or you modified the ACL on the
OU containing an administrative account, and then wondered why the account’s ACL
was overwritten later, you’ve come to the right place. The Admin SD Holder feature of
Active Directory is one that many administrators stumble upon after much grinding of
teeth. However, after you realize the purpose for it, you’ll understand it is a necessary
feature.
Once an hour, a process on the PDC Emulator that we’ll refer to as the Admin SD Holder
process compares the ACL on the AdminSDHolder object to the ACL on the accounts
that are in administrative groups in the domain as well as the groups themselves. If it
detects a difference, it will overwrite the account or Group ACL and disable inheritance.
If you later remove a user from an administrative group, you will need
to reapply any inherited permissions and enable inheritance if neces‐
sary. The Admin SD Holder process will not take care of this for you.
The Admin SD Holder process is intended to subvert any malicious activity by a user
that has been delegated rights over an OU or container that contains an account that is
in one of the administrative groups. An OU administrator could, for example, modify
permissions inheritance on an OU to attempt to lock out the Domain Admins group;
this permission change would be reverted the next time the AdminSDHolder thread runs.
These groups are included as part of Admin SD Holder processing:
• Administrators
• Account Operators
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• Cert Publishers
• Backup Operators
• Domain Admins
• Enterprise Admins
• Print Operators
• Schema Admins
• Server Operators
The administrator and krbtgt user accounts are also specifically checked during the
Admin SD Holder process.
See Also
“Description and Update of the Active Directory AdminSDHolder Object”; “Five com‐
mon questions about AdminSdHolder and SDProp”
14.19. Viewing and Purging Your Kerberos Tickets
Problem
You want to view and purge your Kerberos tickets.
Solution
The kerbtray utility can be found in the Windows Server 2003 Resource Kit. The ker‐
btray utility works through Windows Server 2012. Klist is built into the Active Directory
Domain Services role.
Using a graphical user interface
1. Run kerbtray.exe from the command line or from Start→Run.
2. A new icon (green) should show up in the system tray. Double-click on that icon.
This will allow you to view your current tickets.
3. To purge your tickets, right-click on the kerbtray icon in the system tray and select
Purge Tickets.
4. Close the kerbtray window and reopen it by right-clicking on the kerbtray icon and
selecting List Tickets.
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Using a command-line interface
Run the following command to list your current tickets:
> klist tickets
Run the following command to purge your tickets:
> klist purge
Discussion
Active Directory uses Kerberos as its preferred network authentication system. When
you authenticate to a Kerberos Key Distribution Center (KDC), which in Active Direc‐
tory terms is a domain controller, you are issued one or more tickets. These tickets
identify you as a certain principal in Active Directory and can be used to authenticate
you to other Kerberized services. This type of ticket is known as a ticket-granting tick‐
et, or TGT. Once you’ve obtained a TGT, the client can use the TGT to gain access to a
Kerberized service by querying the Ticket Granting Service on the KDC; if the KDC
verifies that the user is authorized to access the service in question, it will issue a service
ticket that allows the client to use the particular service.
Kerberos is a fairly complicated system, and we can’t do it justice in a single paragraph.
If you want more information on tickets and how the Kerberos authentication system
works, see Kerberos: The Definitive Guide by Jason Garman (O’Reilly).
See Also
RFC 1510 (The Kerberos Network Authentication Service V5); “Kerberos Authentica‐
tion Overview”
14.20. Forcing Kerberos to Use TCP
Problem
Clients are experiencing authentication problems, and you’ve determined it is due to
UDP fragmentation of Kerberos traffic. You want to force Kerberos traffic to use TCP
instead. Perform the solution on all computers that are experiencing the issue (client
computers, server, domain controllers).
Solution
Using a graphical user interface
1. Run regedit.exe from the command line or from Start→Run.
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2. In the left pane, expand HKEY_LOCAL_MACHINE→System→CurrentControlSet→Control→Lsa→Kerberos→Parameters.
3. Right-click on Parameters and select New→DWORD value. Enter MaxPacket
Size for the value name.
4. In the right pane, double-click on MaxPacketSize and enter 1.
5. Click OK.
Using a command-line interface
> reg add "HKLM\SYSTEM\CurrentControlSet\Control\Lsa\Kerberos\Parameters" /v↵
"MaxPacketSize" /t REG_DWORD /d 1
Using VBScript
' This code forces Kerberos to use TCP.
' ------ SCRIPT CONFIGURATION -----
strComputer = "<ComputerName>" ' e.g. rallen-w2k3
' ------ END CONFIGURATION --------
const HKLM = &H80000002
strRegKey = "SYSTEM\CurrentControlSet\Control\Lsa\Kerberos\Parameters"
set objReg = GetObject("winmgmts:\\" & strComputer & ↵
"\root\default:StdRegProv")
objReg.SetDwordValue HKLM, strRegKey, "MaxPacketSize", 1
WScript.Echo "Kerberos forced to use TCP for " & strComputer
Using PowerShell
$strRegPath = "HKLM:\System\CurrentControlSet\Lsa\Kerberos\Parameters"
New-ItemProperty -path $strRegPath -name "MaxPacketSize" -type DWORD
Set-ItemProperty -path $strRegPath -name "MaxPacketSize" -value "1"
Discussion
If you have users that are experiencing extremely slow logon times (especially over VPN)
or they are seeing the infamous “There are currently no logon servers available to service
the logon request” message, then they may be experiencing UDP fragmentation of Ker‐
beros traffic. This occurs because UDP is a connectionless protocol, so UDP packets that
arrive out of order will be dropped by the destination router.
A source of information is the System event log on the clients. Various Kerberos-related
events are logged there if problems with authentication occur.
See Also
“How to force Kerberos to use TCP instead of UDP in Windows”
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14.21. Modifying Kerberos Settings
Problem
You want to modify the default Kerberos settings, such as maximum ticket lifetime.
Solution
Using a graphical user interface
1. Open the Default Domain Group Policy Object, or another domain-linked GPO,
in the Group Policy Management Console.
2. Navigate to Computer Configuration→Policies→Windows Settings→Security Set‐
tings→Account Policies→Kerberos Policy.
3. In the right pane, double-click on the setting you want to modify.
4. Enter the new value and click OK.
Discussion
There are several Kerberos-related settings you can customize, most of which revolve
around either increasing or decreasing the maximum lifetime for Kerberos user and
service tickets. In most environments, the default settings are sufficient, but the ones
you can modify are listed in Table 14-2.
Change the default Kerberos policy settings with caution, as doing so
can cause operational problems and compromise security if done in‐
correctly.
Table 14-2. Kerberos policy settings
Setting Default value
Enforce user logon restrictions Enabled
Maximum lifetime for service ticket 600 minutes
Maximum lifetime for user ticket 10 hours
Maximum lifetime for user ticket renewal 7 days
Maximum tolerance for computer clock synchronization 5 minutes
See Also
“Kerberos Policy”
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14.22. Viewing Access Tokens
Problem
You want to view the access tokens that are created for a user account that has authen‐
ticated to Active Directory.
Solution
Using a command-line interface
> tokensz /compute_tokensize /package:negotiate /target_server:host/<DCName>↵
/user:<Username> /domain:<DomainName> /password:<Password> /dumpgroups
Discussion
When an Active Directory security principal receives a TGT from the Kerberos Key
Distribution Center, the TGT contains a Privilege Attribute Certificate (PAC). This PAC
contains several pieces of authentication data, such as the groups that a user belongs to
(including all nested group memberships). In the majority of AD environments, this
PAC is created without issue, but some larger environments can run into instances of
token bloat. This occurs when a user belongs to a large number of groups (estimates
start at around 70 to 120), and the size of the PAC becomes too large for the TGT to
handle. This issue can manifest itself through authentication issues or through Group
Policy Objects not applying properly. You can download and use the tokensz.exe utility
to compute the token size for a user relative to the maximum allowable size, as well as
to list the groups that a user belongs to.
You can resolve this issue by streamlining the number of groups that the user or users
belong to, which has the added benefit of simplifying the process of assigning permis‐
sions and applying Group Policy Objects. If this isn’t possible, you can apply the hotfix
referenced in MS KB 327825 or modify the HKLM\System\CurrentControlSet\Control
\Lsa\Kerberos\Parameters\MaxTokenSize DWORD value on your domain comput‐
ers. This issue is most relevant on legacy domain controllers, since modern versions of
Windows have made a number of improvements to alleviate the need to modify this
value. Additional details about the recent improvements are in the following “See Also”
section.
If you determine that you need to modify the MaxTokenSize value, use the following
formula as an approximate guideline:
1200 + 40d + 80s
In this equation, 1200 denotes a suggested amount of overhead that’s used by the PAC;
you can use the tokensz utility to determine the size for the domain in question. d refers
to the number of domain local security groups that a representative user is a member
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of, plus any universal security groups in other domains that the user belongs to, plus
any groups represented in the user’s sIDHistory attribute. s refers to the number of
global security groups a representative user belongs to, plus any universal security
groups within the user’s own domain.
See Also
“MaxTokenSize and Windows 8 and Windows Server 2012”; “Whoami” (note that a
new /CLAIMS parameter exists but is not documented on the Whoami site at the time
of this writing)
14.23. Creating a Claim Type
Problem
You want to create a new claim type for Dynamic Access Control.
Solution
Using a graphical user interface
1. Launch the Active Directory Administrative Center.
2. Select Dynamic Access Control and then click Claim Types.
3. From the Tasks menu, click New→Claim Type.
4. Select an Active Directory attribute to use as a source and modify the name and
description, if desired.
5. Select whether to use the claim type for Users, Computers, or both class types.
6. Click OK to create the claim type.
Using PowerShell
The following PowerShell command will create a new claim type:
New-ADClaimType -DisplayName "<DisplayName>" -SourceAttribute "<ADAttribute>"↵
-AppliesToClasses "<ClassType>"
Discussion
Claim types are associated with an Active Directory attribute and are then associated
with the object class. Claim types can be associated with the following Active Directory
classes:
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• User
• Computer
• InetOrgPerson
• msDS-ManagedServiceAccount
• msDS-GroupManagedServiceAccount
See Also
“Dynamic Access Control: Scenario Overview”; New-ADClaimType cmdlet reference;
Active Directory, Fifth Edition, by Brian Desmond et al. (O’Reilly)
14.24. Creating a Resource Property
Problem
You want to create a resource property for Dynamic Access Control.
Solution
Using a graphical user interface
1. Launch the Active Directory Administrative Center.
2. Select Dynamic Access Control and then click Resource Properties.
3. From the Tasks menu click New→Resource Property.
4. Enter a display name for the resource property.
5. Select a value type from the drop-down list to use for the resource property.
6. If required by the value type, click Add in suggested values.
7. Add a value and display name, and then click OK twice.
Using PowerShell
New-ADResourceProperty -DisplayName "<DisplayName>"↵
-ResourcePropertyValueType "<ValueType>"
Discussion
Resource properties are used to authorize access to data. They can be used to describe
and classify files through a manual or automatic classification process. Here is a list of
built-in resource property value types:
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• MS-DS-SingleValuedChoice
• MS-DS-YesNo
• MS-DS-Number
• MS-DS-DateTime
• MS-DS-OrderedList
• MS-DS-Text
• MS-DS-MultiValuedText
• MS-DS-MultiValuedChoice
See Also
“Deploy a Central Access Policy (Demonstration Steps)”; New-ADResourceProperty
cmdlet reference; and Active Directory, Fifth Edition, by Brian Desmond et al. (O’Reilly)
14.25. Configuring a Central Access Rule
Problem
You want to configure a central access rule for Dynamic Access Control.
Solution
Using a graphical user interface
1. Launch the Active Directory Administrative Center.
2. Select Dynamic Access Control and then click Central Access Rules.
3. From the Tasks menu, click New→Central Access Rule.
4. Enter a name for the rule.
5. If necessary, edit the target resources to customize the scope.
6. If necessary, modify the permissions that will apply to the central access rule.
7. Click OK to create the central access rule.
Using PowerShell
New-ADCentralAccessRule -Name "<RuleName>" -ResourceCondition "<Conditions>"↵
-CurrentAcl "<ACL>"
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Discussion
A central access rule assigns permissions to resources under the conditions set on the
target resource. Central access rules are used in central access policies, which are then
applied on a resource, such as a shared folder.
See Also
“Deploy a Central Access Policy (Demonstration Steps)”; New-ADCentralAccessRule
cmdlet reference; Active Directory, Fifth Edition, by Brian Desmond et al. (O’Reilly)
14.26. Creating a Central Access Policy
Problem
You want to create a central access policy.
Solution
Using a graphical user interface
1. Launch the Active Directory Administrative Center.
2. Select Dynamic Access Control and then click Central Access Policies.
3. From the Tasks menu, click New→Central Access Policy.
4. Enter a name for the central access policy.
5. Click Add and select the central access rules to add to the policy by selecting the
rule and clicking the double-arrow icon.
6. Click OK twice to create the policy.
Using PowerShell
New-ADCentralAccessPolicy -Name "<PolicyName>"
Add-ADCentralAccessPolicyMember "<PolicyName>" -Members "<CentralAccessRule>"
Discussion
A central access policy is a collection of central access rules. The policy can be applied
to the resource that will be protected. In the PowerShell solution, first we create the
access policy and then we add in the central access rules as necessary.
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See Also
“Deploy a Central Access Policy (Demonstration Steps)”; Active Directory, Fifth Edi‐
tion, by Brian Desmond et al. (O’Reilly)
14.27. Applying a Central Access Policy
Problem
You want to apply a central access policy by using Group Policy.
Solution
1. Launch the Group Policy Management console.
2. Create and link a GPO, or select an existing GPO to apply the central access policy.
3. Right-click the GPO and click Edit.
4. Navigate to Computer Configuration→Policies→Windows Settings→Security Set‐
tings→File System.
5. Right-click Central Access Policy and select Manage Central Access Policies.
6. Select the central access policy you wish to apply and then click Add. Click OK to
close the configuration dialog box.
Discussion
Central access policies complement existing discretionary access control lists (DACLs)
by providing another layer of permissions for resource access. You can use Group Policy
to effectively and efficiently deploy a central access policy to the specific servers that
need the central access policy settings.
See Also
Recipe 14.27; “Deploy a Central Access Policy (Demonstration Steps)”; Active Directo‐
ry, Fifth Edition, by Brian Desmond et al. (O’Reilly)
14.28. Enabling Domain Controller Support for Claims and
Compound Authentication
Problem
You want to allow domain controllers to provide claims or device authorization.
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Solution
1. Launch the Group Policy Management console (gpmc.msc).
2. Select the Default Domain Controllers Policy or another GPO that applies to all
domain controllers. Right-click the GPO and click Edit.
3. Navigate to Computer Configuration→Policies→Administrative Templates→Sys‐
tem→KDC.
4. Right-click KDS Support for claims, compound authentication, and Kerberos ar‐
moring and select Edit.
5. Click Enabled to enable the configuration and then select Supported from the “op‐
tions” drop-down list.
6. Click OK to close the properties dialog box.
KDC support for claims, compound authentication, and Kerberos ar‐
moring has a couple of options (“Always provide claims” and “Fail un‐
armored authentication requests”) that require that the domain be set
to the Windows Server 2012 domain functional level.
Discussion
For domain controllers to provide claims or device authorization, they must be con‐
figured to support Dynamic Access Control. Changing this setting through the Default
Domain Controllers Policy allows you to modify this setting for all domain controllers
efficiently and effectively.
See Also
Recipe 14.26; Recipe 14.27; “Deploy a Central Access Policy (Demonstration Steps)”;
Active Directory, Fifth Edition, by Brian Desmond et al. (O’Reilly)
14.29. Enabling Claims for Devices in a Domain
Problem
You want to enable claims for devices within a domain.
Solution
1. Launch the Group Policy Management console (gpmc.msc).
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2. Select the Default Domain Policy or another GPO that applies to all domain devices.
Right-click the GPO and click Edit.
3. Navigate to Computer Configuration→Policies→Administrative Templates→Sys‐
tem→Kerberos.
4. Right-click Kerberos Support for claims, compound authentication, and Kerberos
armoring and select Edit.
5. Click Enabled to enable the configuration and then select Supported from the “op‐
tions” drop-down list.
6. Click OK to close the properties dialog box, and then close the Group Policy Man‐
agement console.
7. Launch the Active Directory Administrative Center.
8. Select Dynamic Access Control and then double-click Claim Types.
9. Right-click the claim that you want to modify and then select Properties.
10. Place a checkmark next to Computer and then click OK.
Kerberos support for claims, compound authentication, and Kerberos
armoring requires that there be at least one domain controller running
Windows Server 2012 to support devices running Windows 8.
Discussion
For devices to provide claims, they must be configured to support Dynamic Access
Control. The two-step process described in this recipe allows you to configure claims
for devices within a domain.
See Also
Recipe 14.28; “Deploy a Central Access Policy (Demonstration Steps)”; Active Directo‐
ry, Fifth Edition, by Brian Desmond et al. (O’Reilly)
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CHAPTER 15
Logging, Monitoring, and Quotas
15.0. Introduction
This chapter deals with tracking the activity and usage of various Active Directory
components. When you need to troubleshoot a problem, often the first place you look
is the logfiles. With Active Directory, there are several different logfiles, and each has
different ways to increase or decrease the verbosity of the information that is logged.
Viewing log messages can be a useful troubleshooting step, but you should also look at
performance metrics to determine whether system hardware or a particular service is
being overutilized. In this chapter, we’ll review a couple of ways you can view perfor‐
mance metrics, as well as monitor Active Directory performance. For more extensive
monitoring, we suggest looking at Microsoft System Center Operations Manager
(OpsMgr), or similar products from other vendors such as NetIQ and Quest. In addition
to the typical items that you would monitor on a Windows server (e.g., disk space usage,
physical and virtual memory errors, processor utilization), you should also monitor
AD-specific performance metrics. This extends to monitoring replication activity and
Event Log information.
We’ll also cover a somewhat-related topic called quotas, which allow you to monitor
and limit the number of objects that a security principal (user, group, or computer) can
create within a partition. This feature closes a hole that allowed users who had access
to create as many objects in Active Directory as they wanted. These users could cause
a denial-of-service attack by creating objects until the disk drive on the domain con‐
trollers filled to capacity. This kind of attack is not likely to happen in most environ‐
ments, but you should still consider the possibility and protect against it.
The Anatomy of a Quota Object Container
Quota objects are stored in the NTDS Quotas container of the naming contexts and
application partitions except for the schema naming context. (Quotas cannot be
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associated with the schema NC.) By default, this container is hidden from view within
tools such as Active Directory Users and Computers, but you can see it by selecting
View→Advanced Features from the menu. The quota object container has an object
Class of msDS-QuotaContainer and contains several attributes that define default quota
behavior. Table 15-1 lists some of the important attributes of msDS-QuotaContainer
objects.
Table 15-1. Attributes of msDS-QuotaContainer objects
Attribute Description
cn RDN of quota container objects. By default, this is equal to NTDSQuotas.
msDS-DefaultQuota The default quota applied to all security principals that do not have
another quota specification applied. See Recipe 15.18 for more details.
msDS-QuotaEffective A constructed attribute that contains the effective quota of the security
principal that is viewing the attribute. See Recipe 15.19 for more details.
msDS-QuotaUsed A constructed attribute that contains the quota usage of the security
principal that is viewing the attribute. See Recipe 15.19 for more details.
msDS-TombstoneQuotaFactor Percentage that tombstone objects count against a quota. The default is
100, which means a tombstone object has equal weighting to a normal
object. See Recipe 15.17 for more details.
msDS-TopQuotaUsage Multivalued attribute that contains information about the security
principals with the top quota usage. See Recipe 15.19 for more details.
The Anatomy of a Quota Object
Quota objects have an objectClass of msDS-QuotaControl, which defines three at‐
tributes that relate to quotas. Table 15-2 contains these attributes and provides a de‐
scription for each.
Table 15-2. Attributes of msDS-QuotaControl objects
Attribute Description
cn RDN of the quota object.
msDS-QuotaAmount Number of objects that can be created by the security principals that the quota applies to. See
Recipe 15.15 for more information.
msDS-QuotaTrustee SID of the security principal that the quota applies to. This can be a user, group, or computer SID. See
Recipe 15.15 for more information.
15.1. Enabling Diagnostics Logging
Problem
You want to enable diagnostics event logging because the current level of logging is not
providing enough information to help pinpoint the problem you are troubleshooting.
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Solution
Using a graphical user interface
1. Run regedit.exe from the command line or from Start→Run.
2. In the left pane, expand the following Registry key: HKEY_LOCAL_MACHINE
\System\CurrentControlSet\Services\NTDS\Diagnostics.
3. In the right pane, double-click on the diagnostics logging entry you want to increase,
and enter a number (0–5) based on how much you want logged.
4. Click OK.
Using a command-line interface
> reg add HKLM\SYSTEM\CurrentControlSet\Services\NTDS\Diagnostics /v↵
"<LoggingSetting>" /t REG_DWORD /d <0-5>
Using PowerShell
Set-ItemProperty -Path "HKLM:\SYSTEM\CurrentControlSet\Services\NTDS\↵
Diagnostics" -Name "<LoggingSetting>" -Value "<FlagValue>"
Discussion
A useful way to troubleshoot specific problems you are encountering with Active Di‐
rectory is to increase the diagnostics logging level. Diagnostics logging can be enabled
for individual components of AD. For example, if you determine the KCC is not com‐
pleting every 15 minutes, you can enable diagnostics logging for the “1 Knowledge
Consistency Checker” setting.
These settings are stored under HKLM\SYSTEM\CurrentControlSet\Services\NTDS
\Diagnostics. By default, all settings are set to 0, which disables diagnostics logging, but
you can increase it by setting it to a number from 1 through 5. As a general rule, a value
of 1 is used for minimum logging, 3 for medium logging, and 5 for maximum logging.
It is a good practice to ease your way up to 5 because some diagnostics logging settings
can generate a bunch of events in the event log, which may make it difficult to read,
along with increasing resource utilization on the domain controller.
Here is the complete list of diagnostics logging settings:
1 Knowledge Consistency Checker
2 Security Events
3 ExDS Interface Events
4 MAPI Interface Events
5 Replication Events
6 Garbage Collection
7 Internal Configuration
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8 Directory Access
9 Internal Processing
10 Performance Counters
11 Initialization/Termination
12 Service Control
13 Name Resolution
14 Backup
15 Field Engineering
16 LDAP Interface Events
17 Setup
18 Global Catalog
19 Inter-site Messaging
20 Group Caching
21 Linked-Value Replication
22 DS RPC Client
23 DS RPC Server
24 DS Schema
25 Transformation Engine
26 Claims-Based Access Control
See Also
“Active Directory Diagnostic Logging”
15.2. Enabling NetLogon Logging
Problem
You want to enable NetLogon logging to help with troubleshooting client account logon,
lockout, or domain controller location issues.
Solution
Using a command-line interface
To enable NetLogon logging, use the following command:
> nltest /dbflag:0x2080ffff
To disable NetLogon logging, use the following command:
> nltest /dbflag:0x0
Discussion
The netlogon.log file located in %SystemRoot%\Debug can be invaluable for trouble‐
shooting client logon and related issues. When enabled at the highest setting
(0x2080ffff), it logs useful information such as the site the client is in, the domain con‐
troller the client authenticated against, additional information related to the DC Locator
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process, account password expiration information, account lockout information, and
even Kerberos failures.
The NetLogon logging level is stored in the following Registry value:
HKLM\System\CurrentControlSet\Services\Netlogon\Parameters\DBFlag
If you set that Registry value manually instead of using nltest, you’ll
need to create the string value, adjust the value, and then restart the
NetLogon service for it to take effect.
One of the issues with the netlogon.log file is that it can quickly grow to several mega‐
bytes, which makes it difficult to peruse. The command-line tool nlparse can filter the
contents of the netlogon.log file so that you’ll see only certain types of log entries. The
nlparse tool is part of the Account Lockout and Management Tools.
See Also
MS KB 109626 (Enabling Debug Logging for the Netlogon Service); MS KB 247811
(How Domain Controllers Are Located in Windows); MS KB 273499 (Description of
Security Event 681); “Troubleshooting Netlogon Error Codes”
15.3. Enabling GPO Client Logging
Problem
You want to troubleshoot GPO processing issues on a client or server by enabling ad‐
ditional logging in the Application event log.
Solution
Using a graphical user interface
1. Run regedit.exe from the command line or from Start→Run.
2. In the left pane, expand the appropriate key from the table in this recipe’s “Discus‐
sion” section.
3. Create and populate the appropriate key value.
4. Click OK.
Using a command-line interface
> reg add "<Key Value>" /v "<ValueName>" /t REG_DWORD /d <Value>
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Using PowerShell
Set-ItemProperty -Path "<RegistryKeyPath>" -Name "<ValueName>" -Value "<Value>"
Discussion
If you experience problems with client GPO processing, such as a GPO not getting
applied even though you think it should, there are a number of different Registry keys
that can help you troubleshoot the problem. One way to get detailed information about
which GPOs are applied on a client computer is by enabling additional GPO event
logging. Table 15-3 lists a number of Registry settings that can be configured to enable
Group Policy logging, as well as the files that are created when the settings are enabled.
Table 15-3. Registry settings to enable Group Policy logging
Logging for the CSE Location Enable verbose logging by adding
this key or value ...
...to this Registry key
Security CSE %windir%\security
\logs\winlogon.log
ExtensionDebugLevel = REG_DWORD 0x2 HKEY_LOCAL_MACHINE\Software
\Microsoft\Windows NT
\CurrentVersion\Winlogon
\GpExtensions
\{827d319e-6eac-11d2-
a4ea-00c04f79f83a}\
Folder Redirection
CSE
windir%\debug
\usermode
\fdeploy.log
FdeployDebugLevel = Reg_DWORD 0x0f HKEY_LOCAL_MACHINE\Software
\Microsoft\Windows NT
\CurrentVersion\Diagnostics
Software Installation
CSE
%windir%\debug
\usermode
\appmgmt.log
Appmgmtdebuglevel=dword:0000009b HKEY_LOCAL_MACHINE\Software
\Microsoft\Windows NT
\CurrentVersion\Diagnostics
Windows Installer
(deployment-related
actions)
%windir%\temp
\MSI*.log
Logging = voicewarmup Debug =
DWORD: 00000003
HKEY_LOCAL_MACHINE\Software
\Policies\Microsoft\Windows\Installer
Windows Installer
(user-initiated
actions)
%temp%\MSI*.log Logging = voicewarmup Debug =
DWORD: 00000003
HKEY_LOCAL_MACHINE\Software
\Policies\Microsoft\Windows\Installer
See Also
“Fixing Group Policy problems by using log files”; “Troubleshooting Group Policy Us‐
ing Event Logs”; “Userenvlog for Windows Vista/2008/Win7”
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15.4. Enabling Kerberos Logging
Problem
You want to enable Kerberos logging on a domain controller to troubleshoot authenti‐
cation problems.
Solution
Using a graphical user interface
1. Run regedit.exe from the command line or from Start→Run.
2. In the left pane, expand HKEY_LOCAL_MACHINE\System\CurrentControlSet
\Control\Lsa\Kerberos\Parameters.
3. If the LogLevel value doesn’t already exist, right-click on Parameters and select
New→DWORD value. Enter LogLevel for the value name and click OK.
4. In the right pane, double-click on LogLevel and enter 1.
5. Click OK.
Using a command-line interface
> reg add HKLM\SYSTEM\CurrentControlSet\Control\Lsa\Kerberos\Parameters↵
/v "LogLevel" /t REG_DWORD /d 1
Using PowerShell
Set-ItemProperty -Path↵
"HKLM:\SYSTEM\CurrentControlSet\Control\Lsa\Kerberos\Parameters" -Name↵
"LogLevel" -Value "1"
Discussion
If you are experiencing authentication problems or would like to determine whether
you are experiencing any Kerberos-related issues, enabling Kerberos logging will ensure
that Kerberos errors will be logged in the System event log. The Kerberos events can
point out if the problem is related to clock skew, an expired ticket, an expired password,
etc. For a good overview of some of the Kerberos error messages, see MS KB 230476.
Here is a sample event:
Event type: Error
Event source: Security-Kerberos
Event ID: 3
A Kerberos error message was received:
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on logon session user5@adatum
ClientTime
ServerTime 19:34:26.0000 12/17/2012 Z
ErrorCode 0x17
ErrorMessage 0x19 KDC_ERR_PREAUTH_REQUIRED
ExtendedError
ClientRealm
ClientName
ServerRealm ADATUM.COM
ServerName krbtgt/ADATUM.COM
TargetName krbtgt/ADATUM.COM@ADATUM.COM
ErrorText
File e
Line d3a
Error Data is in record data.
See Also
“How to enable Kerberos event logging”
15.5. Viewing DNS Server Performance Statistics
Problem
You want to view DNS server performance statistics.
Solution
Using a graphical user interface
1. Open the Performance Monitor.
2. Click on Performance Monitor in the left pane.
3. In the right pane, click the + button. This will bring up the page to add counters.
4. Under “Select counters from computer”, enter the DNS server you want to target.
5. Select the DNS performance object.
6. Select the counters you want to add and click the Add button.
7. Click Close.
Using a command-line interface
> dnscmd <DNSServerName> /statistics
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Using PowerShell
Get-EventLog "DNS Server"
Discussion
The Microsoft DNS Server keeps track of dozens of performance metrics. These metrics
include the number of queries, updates, transfers, directory reads, and directory writes
processed by the server. If you can pump these metrics into an enterprise management
system, you can track DNS usage and growth over time.
These statistics can also be useful to troubleshoot load-related issues. If you suspect a
DNS server is being overwhelmed with DNS update requests, you can look at the Dy‐
namic Update Received/sec counter and see whether it is processing an unusually high
number of updates.
Using a command-line interface
You can obtain a subset of the statistics by providing a statid after the /statistics
option. Each statistics category has an associated number (i.e., statid). For a complete
list of categories and their statids, run the following command:
> dnscmd /statistics /?
Here is an example of viewing the Query (statid = 2) and Query2 (statid = 4)
statistics:
> dnscmd /statistics 6
DNS Server . statistics:
Queries and Responses:
----------------------
Total:
Queries Received = 14902
Responses Sent = 12900
UDP:
Queries Recvd = 14718
Responses Sent = 12716
Queries Sent = 23762
Responses Recvd = 0
TCP:
Client Connects = 184
Queries Recvd = 184
Responses Sent = 184
Queries Sent = 0
Responses Recvd = 0
Queries:
--------
Total = 14902
Notify = 0
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Update = 2207
TKeyNego = 184
Standard = 12511
A = 1286
NS = 29
SOA = 2263
MX = 0
PTR = 1
SRV = 8909
ALL = 0
IXFR = 0
AXFR = 0
OTHER = 23
Command completed successfully.
See Also
MSDN: MicrosoftDNS_Statistic
15.6. Monitoring the Windows Time Service
Problem
You want to verify the correct functioning of the Windows Time Service.
Solution
Using a command-line interface
The following syntax verifies that the Windows Time Service is functioning on dc1.ada‐
tum.com and dc2.adatum.com:
> w32tm /monitor /computers:dc1.adatum.com,dc2.adatum.com
Discussion
Because Active Directory relies on Kerberos for authentication, it’s critical that all of
your domain controllers, member servers, and client computers maintain a consistent
time across the network; if any computer’s clock is off by more than five minutes, then
by default, it will not be able to authenticate to Active Directory. You can use the w32tm
utility to verify time synchronization on one or more computers using the /monitor
switch, as well as using the /resync switch to prompt a computer to immediately re‐
synchronize its clock with its authoritative time source.
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See Also
“Configuring a Time Source for the Forest”; “How to configure an authoritative time
server in Windows Server”
15.7. Enabling Inefficient and Expensive LDAP
Query Logging
Problem
You want to log inefficient and expensive LDAP queries to the Directory Services event
log.
Solution
To log a summary report about the total number of searches, total expensive searches,
and total inefficient searches to the Directory Services event log, set the 15 Field Engi‐
neering diagnostics logging setting to 4. This summary is generated every 12 hours
during the garbage collection cycle.
To log an event to the Directory Services event log every time an expensive or inefficient
search occurs, set the 15 Field Engineering diagnostics logging setting to 5.
See Recipe 15.1 for more on enabling diagnostics logging.
Discussion
A search is considered expensive if it has to visit a large number of objects in Active
Directory. The default threshold for an expensive query is 10,000. That means any search
that visits 10,000 or more objects would be considered expensive. A search is considered
inefficient if it returns fewer than 10 percent of the total objects it visits. If a query visited
10,000 objects and only returned 999 of them (less than 10 percent), it would be con‐
sidered inefficient. The default bottom limit for an inefficient query is 1,000. If the query
returned 1,000 instead, it would not be considered inefficient. To summarize, with 1,000
as the default bottom threshold, no search that visits fewer than 1,000 entries (even if it
visited 999 and returned 0) would be considered inefficient.
Here is a sample summary report event that is logged when 15 Field Engineering is set
to 5:
Log Name: Directory Service
Source: Microsoft-Windows-ActiveDirectory_DomainService
Date: 12/21/2012 11:38:32 PM
Event ID: 1643
Task Category: Field Engineering
Level: Information
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Keywords: Classic
User: ANONYMOUS LOGON
Computer: adatum-dc.adatum.com
Description:
Internal event: Active Directory Domain Services performed the following number↵
of search operations within this time interval.
Time interval (hours):
0
Number of search operations:
38529
During this time interval, the following number of search operations were↵
characterized as either expensive or inefficient.
Expensive search operations:
7
Inefficient search operations:
22
If you set 15 Field Engineering to 5, the summary event is logged during the garbage
collection cycle, and event 1644 is generated every time an expensive or inefficient
search occurs. Setting this value can provide useful information if you are running
applications that regularly generate expensive or inefficient queries. Notice that this
event provides details on all aspects of the search, including the authenticating user,
search base DN, search filter, attributes, controls, number of entries visited, and number
of entries returned. The following entry is from a Windows Server 2012 domain con‐
troller:
Log Name: Directory Service
Source: Microsoft-Windows-ActiveDirectory_DomainService
Date: 12/22/2012 1:19:05 AM
Event ID: 1644
Task Category: Field Engineering
Level: Information
Keywords: Classic
User: SYSTEM
Computer: dc1.adatum.com
Description:
Internal event: A client issued a search operation with the following options.
Client:
SAM
Starting node:
dc=adatum,dc=com
Filter:
( & (userAccountControl&2) (objectClass=user)
(objectCategory=cn=Person,cn=Schema,cn=Configuration,dc=adatum,dc=com) )
Search scope:
subtree
Attribute selection:
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[shortnames]objectSid,sAMAccountName,userAccountControl
Server controls:
Visited entries:
51443
Returned entries:
3513
With the default settings, the query shown in the preceding event is considered both
expensive and inefficient. It is expensive because it visited more than 10,000 entries. It
is inefficient because it returned fewer than 10 percent of those entries.
You can customize what a domain controller considers expensive and inefficient by
creating a couple of Registry values under the HKLM\SYSTEM\CurrentControlSet
\Services\NTDS\Parameters key. You can create a value named Expensive Search Re
sults Threshold of type DWORD and specify the number of entries a search would need
to visit to be considered expensive. Similarly, you can create a value named Inefficient
Search Results Threshold of type DWORD and specify the minimum number of entries
visited where a match returning fewer than 10 percent would be considered inefficient.
If you want to see all the LDAP queries that are being sent to a domain
controller, a quick way to do that would be to set the 15 Field Engi‐
neering setting to 5 and Expensive Search Results Threshold to 0. This
would cause the domain controller to consider every search as expen‐
sive and log all the LDAP searches. While this can be very useful, you
should use it with care as it could quickly fill your event log. Be sure to
allow sufficient disk space for your event logs to avoid any issues with
low disk space on your domain controllers.
See Also
Recipe 15.1 for enabling diagnostics logging
15.8. Using the STATS Control to View LDAP Query
Statistics
Problem
You want to use the STATS LDAP control to test the efficiency of a query.
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Solution
Using a graphical user interface
1. Launch LDP.exe.
2. From the menu, select Connection→Connect.
3. For Server, enter the name of a domain controller.
4. For Port, enter 389.
5. Click OK.
6. From the menu, select Connection→Bind.
7. Enter the credentials of a user to perform the search or accept the default and bind
as the currently logged on user.
8. Click OK.
9. From the menu, select Options→Controls.
10. From the Load Predefined drop-down, select Search Stats.
11. Click OK.
12. From the menu, select Browse→Search.
13. Enter your search criteria and then click the Options button.
14. Under Search Call Type, be sure that Extended is selected.
15. Click OK and then click Run. The status will be shown at the top of the search
results.
Using a command-line interface
The AdFind command-line utility has four switches that will display efficiency statistics
for any query:
-stats
Enables the STATS control to return statistics about the query, along with the actual
results of the query
-statsonly
Returns only the statistics about the query, and suppresses the actual query results
-stats+
Similar to -stats, but also displays additional advanced analysis about the query
-stats+only
Just like -stats+, but will suppress the actual results of the query and display only
the query statistics
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Discussion
The STATS control is a useful way to obtain statistics about the performance of an LDAP
query. With the STATS control, you can find out information such as the amount of
time it took the server to process the query, how many entries were visited versus re‐
turned, what the search filter expanded to, and whether any indexes were used. Here is
an example of what the STATS control returns for a search for all group objects in the
cn=Users container:
Statistics
==================================================
Elapsed time: 0 (ms)
Returned 18 of 23 visited - (78.26%)
Used Filter:
(objectCategory=cn=Group,cn=Schema,cn=Configuration,cn=adatum,cn=com
Used Indices:
Ancestors_index:23:N
Pages referenced: 332
Pages read from disk: 0
Pages pre-read from Disk: 0
Analysis
--------------------------------------------------
Indices used:
Index name: Ancestors_index
Record count: 23 (estimate)
Index type: Normal attribute index
Ancestor index used, possibly inefficient, verify filter
A couple of things are worth noting here. You can also see that the filter used, (object
category=group), was expanded to:
(objectCategory=cn=Group,cn=Schema,cn=Configuration,dc=adatum,dc=com)
The syntax of the objectCategory attribute is a distinguished name, but Active Direc‐
tory provides a shortcut so that you need to use only the LDAP display name of the class
instead. Internally, Active Directory converts the display name to the distinguished
name, as shown here. Finally, we can see that our search used an index, INTERSECT_IN
DEX:17:I.
Let’s look at another example, except this time we’ll perform an ANR search for Jim
Smith:
***Searching ...
ldap_search_ext_s(ld, "ou=Sales,dc=adatum,dc=com", 2, "(anr=Jim Smith)",
attrList, 0, svrCtrls, ClntCtrls, 20, 1000 ,&msg)
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Result <0>:
Matched DNs:
Stats:
Call Time: 20 (ms)
Entries Returned: 1
Entries Visited: 2
Used Filter: ( | (displayName=Jim Smith*) (givenName=Jim Smith*)
(legacyExchangeDN=Jim Smith) (msDS-AdditionalSamAccountName=Jim Smith*)
(physicalDeliveryOfficeName=Jim Smith*) (proxyAddresses=Jim Smith*) (name=Jim
Smith*) (sAMAccountName=Jim Smith*)
(sn=Jim Smith*) ( & (givenName=Jim*) (sn=Smith*) ) ( & (givenName=Smith*)
(sn=Jim*) ) )
Used Indexes:
idx_givenName:10:N;idx_givenName:10:N;idx_sn:9:N;idx_
sAMAccountName:8:N;idx_name:7:N;idx_proxyAddresses:6:N;idx_
physicalDeliveryOfficeName:5:N;idx_msDS-AdditionalSamAccountName:4:N;idx_
legacyExchangeDN:3:N;idx_givenName:2:N;idx_displayName:1:N;
You can see from the second line that we used a very simple filter, (anr=Jim Smith). If
you look down a little farther at Used Filter: you can see a better example of searchfilter expansion. Like the objectCategory example earlier, ANR is a shorthand way to
do something complex. A simple one-term search filter expands into a multiterm filter
that searches across numerous attributes. (For more on the behavior of ANR, see
Recipe 10.12.) The point of showing this is to illustrate that the STATS control is very
powerful and can be an invaluable tool when trying to troubleshoot or optimize LDAP
queries.
See Also
Recipe 4.4 for using LDAP controls; Recipe 4.8 for searching for objects; Recipe 10.12
for more on ANR; Recipe 15.7 for more on expensive and inefficient searches
15.9. Monitoring the Performance of Active Directory
Problem
You want to use the Performance Monitor to examine the performance of Active
Directory.
Solution
Using a graphical user interface
1. Open the Performance Monitor (perfmon.exe).
2. Click on Performance Monitor in the left pane.
3. Click the + button. This will bring up the page to add counters.
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4. Under “Select counters from computer”, enter the name of the domain controller
you want to target.
5. Select the NTDS performance object.
6. Select the counters that you want to monitor.
7. After you’re done with your selections, click Close.
Using PowerShell
To retrieve a continuous counter for a performance object, use the following PowerShell
command:
Get-Counter -Counter "<PerformanceObject>" -Continuous
For example, to view the performance counter for the DS Directory Searches/sec
object, run the following command:
Get-Counter -Counter "\NTDS\DS Directory Searches/sec" -Continuous
Discussion
There are several Performance Monitor counters that can be very valuable for moni‐
toring and troubleshooting Active Directory. The NTDS performance object has coun‐
ters for address-book lookups; inbound and outbound replication; LDAP reads, writes,
and searches; and the Security Account Manager (SAM).
Here is a list of some of the most useful NTDS counters. We’ve also included their
Performance Monitor explanation, which you can view by clicking on the Explain but‐
ton in the Add Counters dialog box.
DRA Inbound Bytes Total/sec
Shows the total number of bytes received through replication. It is the sum of the
number of uncompressed bytes (never compressed) and the number of compressed
bytes (after compression).
DRA Inbound Objects/sec
Shows the number of objects received from neighbors through inbound replication.
A neighbor is a domain controller from which the local domain controller replicates
locally.
DRA Inbound Values Total/sec
Shows the total number of object property values received from inbound replication
partners. Each inbound object has one or more properties, and each property has
zero or more values. A zero value indicates property removal.
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DRA Outbound Bytes Total/sec
Shows the total number of bytes replicated out. It is the sum of the number of
uncompressed bytes (never compressed) and the number of compressed bytes (after
compression).
DRA Outbound Objects/sec
Shows the number of objects replicated out.
DRA Outbound Values Total/sec
Shows the number of object property values sent to outbound replication partners.
DRA Pending Replication Synchronizations
Shows the number of directory synchronizations that are queued for this server but
not yet processed.
DS Client Binds/sec
Shows the number of ntdsapi.dll binds per second serviced by this DC.
DS Directory Reads/sec
Shows the number of directory reads per second.
DS Directory Searches/sec
Shows the number of directory searches per second.
DS Directory Writes/sec
Shows the number of directory writes per second.
LDAP Bind Time
Shows the time, in milliseconds, taken for the last successful LDAP bind.
LDAP Client Sessions
Shows the number of currently connected LDAP client sessions.
LDAP Searches/sec
Shows the rate at which LDAP clients perform search operations.
LDAP Successful Binds/sec
Shows the number of LDAP binds per second.
LDAP Writes/sec
Shows the rate at which LDAP clients perform write operations.
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15.10. Using Perfmon Trace Logs to Monitor
Active Directory
Problem
You want to enable Trace Logs to view system-level calls related to Active Directory.
Solution
Using a graphical user interface
1. Open the Performance Monitor (perfmon.exe).
2. In the left pane, expand Data Collector Sets.
3. Right-click Event Trace Sessions and click New→Data Collector Sets.
4. In the Name: field, enter AD Trace Log. Click Next.
5. Click Add. In the Event Trace Providers screen, click Active Directory Domain
Services: Core. Click OK.
6. Click Next, note the directory to be used for the log, and then click Next again.
7. Click the “Start this data collector set now” radio button and click Finish.
8. Open a command prompt and run the following command:
tracerpt <LogFileName>
Discussion
Trace Logs capture detailed system- and application-level events. Applications support
Trace Log capability by developing a Trace Log Provider. Active Directory supports
several providers that log low-level system calls related to Kerberos, LDAP, and DNS,
to name a few. This can be an extremely valuable tool for debugging or just exploring
the inner workings of Active Directory. Trace Logs can be resource-intensive, so you
should enable them with care.
The tracerpt/tracedmp commands generate a summary.txt file that summarizes all of
the events by total. A second file called dumpfile.xml is created by default, but the dump
format can be changed by specifying the -of switch, with a CSV, EVTX, or XML value.
Here is an example of what the summary.txt file looks like on a domain controller that
had all of the Active Directory−related Trace Log Providers enabled:
Files Processed:
AD Trace Log.etl
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Total Buffers Processed 18
Total Events Processed 720
Total Events Lost 0
Start Time Saturday, December 22, 2012
End Time Saturday, December 22, 2012
Elapsed Time 51 sec
+--------------------------------------------------------------------------------+
|Event Count Event Name Task Opcode Version Guid
+--------------------------------------------------------------------------------+
| 1 EventTrace 0 DbgIdRSDS 2 {68fdd900-4a3e-11d1↵
-84f4-0000f80464e3}|
| 1 EventTrace 0 BuildInfo 2 {68fdd900-4a3e-11d1↵
-84f4-0000f80464e3}|
| 1 EventTrace 0 Header 2 {68fdd900-4a3e-11d1↵
-84f4-0000f80464e3}|
| 2 DsDrsReplGtChg 0 End 4 {14f8aa24-7f4b-11d2↵
-b389-0000f87a46c8}|
| 2 DsDrsReplGtChg 0 Start 4 {14f8aa24-7f4b-11d2↵
-b389-0000f87a46c8}|
| 125 LdapRequest 0 End 4 {b9d4702a-6a98-11d2↵
-b710-00c04fb998a2}|
+--------------------------------------------------------------------------------+
Here you can see that over a 51-second period, there was one Event Trace request
(EventTrace), two directory replication change requests (DsDrsReplGtChg), and 125
total LDAP requests (LdapRequest).
The dumpfile.csv file contains entries for every event that was generated during the time
period. Here is an example of an entry for one of the DsDrsReplGtChg requests (note
that the lines will wrap due to their length, so we’ve added a blank line in between for
separation):
DsDrsReplGtChg, Start, 0, 4, 0, 0,
1, 0, 0x0000000000000000, 0x00000240, 0x00001388,
0, , ,
{00000000-0000-0000-0000-000000000000},
, 130006457569095598, 15, 0, "DS", 4, 8, 3506765888, 0,
"e5a1b109-4add-4503-a909-66e55820265c (DC2.adatum.com)", "dc=adatum,dc=com",
"250469",
"250469", "2147483760", "536", "5363998", "0",
0x00000000000000000000A7E12200CD00
DsDirGtNcChg, Start, 0, 4, 0, 0,
1, 0, 0x0000000000000000, 0x00000240, 0x00001388,
0, , ,
{00000000-0000-0000-0000-000000000000},
, 130006457569097056, 15, 0, "DS", 4, 6, 805568576, 0,
"e5a1b109-4add-4503-a909-66e55820265c (DC2.adatum.com)", "dc=adatum,dc=com",
"250469", "80000070", "0", "0", 0x47D92200CD000000A820303D
Based on those two lines, you can see Active Directory Domain Services replication
commutation occur from this server to another server named dc2.adatum.com.
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15.11. Creating an Administrative Alert
Problem
You want to define a threshold for a performance counter that should cause an alert to
be generated.
Solution
Using a graphical user interface
1. Open the Performance Monitor (perfmon.exe).
2. Expand Data Collector Sets. Right-click User-Defined and click New→Data Col‐
lector Set.
3. In the Name text box, enter AD Performance Alert. Select the “Create manually”
radio button and click Next.
4. Click the Performance Counter Alert radio button and click Next.
5. Click Add. Select the counter that you wish to be alerted about. Click Add and click
OK.
6. In the “Alert when:” drop-down box, click Above or Below. In the Limit text box,
enter the threshold value that you wish to monitor. Click Next.
7. Click the “Start this data collector now” radio button. Click Finish.
Discussion
There are a number of options for monitoring the ongoing performance of the Windows
operating system, whether the machine in question is a domain controller, member
server, or client computer. For larger environments, you can look into add-on tools such
as the Microsoft System Center Operations Manager (OpsMgr) or third-party utilities
from NetPro, NetIQ, and others. For a built-in solution, however, the Performance
Monitor MMC snap-in can monitor performance metrics and send various adminis‐
trative alerts.
See Also
“Windows Performance Monitor”
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15.12. Emailing an Administrator on a Performance Alert
Problem
You want to create an alert that will notify an administrator via email if a performance
alert is generated.
Solution
Using PowerShell
You can create a Windows scheduled task that runs the following PowerShell command.
Then, the task can be called from a performance counter alert in Performance Monitor.
Send-MailMessage -SmtpServer "<ServerName>" -From "<FromAddress>"↵
-To "<ToAddress>" -Subject "<MessageSubject>" -Body "<MessageBody>"
Discussion
A common request among Windows system administrators is to have the ability to
email an on-call administrator when a critical performance alert is generated—for ex‐
ample, when a domain controller is experiencing a critical hardware failure. It is a rel‐
atively simple matter to send email through PowerShell using the sample command
shown in the solution. You can either hardcode the appropriate alert messages into the
email message and maintain multiple scripts for the various alerts that you create, or
include counter information in each message by using a generic email message (see
Recipe 15.9). Using the Performance Monitor MMC, you can submit one or more of
the following as command-line arguments to a script that’s been fired in response to an
alert:
• Date/time
• The value that was measured by the alert
• The name of the alert
• The name of the counter being measured
• The value of the limit that was exceeded
• A manually defined text string
You can also use a number of third-party tools to implement this solution, such as
the open-source Blat SourceForge project, which allows you to send SMTP or
NNTP messages from a command line.
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See Also
Send-MailMessage cmdlet overview
15.13. Enabling Auditing of Directory Access
Problem
You want to enable auditing of directory access and modifications. Audit events are
logged to the Security event log.
Solution
Using a graphical user interface
1. Open the Group Policy Management snap-in (gpmc.msc) and edit the Default Do‐
main Controllers Policy.
2. In the left pane, expand Computer Configuration→Policies→Windows Set‐
tings→Security Settings→Local Policies and click on Audit Policy.
3. In the right pane, double-click “Audit directory service access.”
4. Make sure the box is checked beside “Define these policy settings.”
5. Check the box beside Success and/or Failure.
6. Click OK.
Alternatively, you can also use the Advanced Audit Policy Configuration settings, which
allow for a bit more granularity:
1. Open the Group Policy Management snap-in (gpmc.msc) and edit the Default Do‐
main Controllers Policy.
2. In the left pane, expand Computer Configuration→Policies→Windows Set‐
tings→Security Settings→Advanced Audit Configuration Policy and click on Audit
Policies.
3. In the right pane, double-click “DS access.”
4. In the right pane, enable “Success and/or Failure auditing” for the Audit Directory
Service Access and the Audit Directory Service Changes subcategories.
Discussion
You can log events to the Security event log for every successful and/or failed attempt
to access or modify the directory, which is referred to as auditing. Auditing is enabled
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via the Security Settings section of a GPO that’s linked to the Domain Controllers OU,
using either the “Audit directory service access” setting or the “Advanced Audit Policy
Configuration” settings. Once either is enabled, you need to use the ACL Editor to define
auditing in the SACL of the objects and containers you want to monitor.
By default, the domain object has an inherited audit entry for the Everyone security
principal for all object access and modifications. That means once you enable auditing
in the Domain Controller Security Policy and this configuration change replicates out,
domain controllers will log events for any directory access or modification to any part
of the directory. As you can imagine, auditing every access to Active Directory can
generate a lot of events, so you’ll either want to disable auditing of the Everyone group
and use the Advanced Audit Policy Configuration settings instead, or else keep a close
eye on your domain controllers to ensure that they are not adversely affected while
auditing is enabled.
Here is a sample event that was logged after the Administrator account created a user
object called foobar in the Sales OU:
Event Type: Audit Success
Event Source: Microsoft Windows security
Task Category: User Account Management
Event ID: 4720
Date: 12/26/2012
Time: 7:24:10 PM
User: N/A
Computer: DC1
A user account was created.
Subject:
Security ID: ADATUM\administrator
Account Name: administrator
Account Domain: ADATUM
Logon ID: 0x36BFF
New Account:
Security ID: ADATUM\foobar
Account Name: foobar
Account Domain: ADATUM
Attributes:
SAM Account Name: foobar
Display Name: foobar
User Principal Name: foobar@adatum.com
Home Directory: -
Home Drive: -
Script Path: -
Profile Path: -
User Workstations: -
Password Last Set: <never>
Account Expires: <never>
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Primary Group ID: 513
Allowed To Delegate To: -
Old UAC Value: 0x0
New UAC Value: 0x15
User Account Control:
Account Disabled
'Password Not Required' - Enabled
'Normal Account' - Enabled
User Parameters: -
SID History: -
Logon Hours: <value not set>
Additional Information:
Privileges -
It can also be useful to enable Audit Account Management in the GPO
that’s linked to the Domain Controllers OU. This provides additional
information about account-management operations—for example,
finding what account deleted a certain object.
Once you have enabled auditing of Directory Service Changes and configured auditing
on the relevant objects or containers, the Directory Services Event Viewer will record
detailed entries whenever an AD object is created, modified, moved, or deleted, as
follows:
• Event 4738 will be logged when an object is modified. In the case of a modify event,
you will see the old value (e.g., the old description attribute) and the new value (e.g.,
the new description attribute).
• Event 4720 will be logged when an object is created.
• Event 4725 will be logged when an object is disabled.
• Event 4740 will be logged when an object is locked out.
• Event 4726 will be logged when an object is deleted.
See Also
“Advanced Security Audit Policy Settings”; “Planning and Deploying Advanced Security
Audit Policies”
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15.14. Enabling Auditing of Registry Keys
Problem
You want to enable auditing of any changes to one or more Registry keys.
Solution
Using a graphical user interface
To enable auditing of a Registry key on an individual domain controller, do the
following:
1. Create a Group Policy Object (or edit an existing GPO) that enables settings under
the following path: Computer Configuration→Policies→Windows Settings→Se‐
curity Settings→Local Policies→Audit Policy:
• Audit object access: Success
• Audit object access: Failure
2. Link the GPO to the OU containing the DC that you wish to audit.
3. On the DC that you want to audit, open regedit.exe.
4. Navigate to the Registry key that you want to enable auditing on.
5. Right-click on the key and select Permissions. Click Advanced and select the Au‐
diting tab.
6. Click Add to select a user or group to audit, then click OK. For Apply Onto, select
“This key only,” “This key and subkeys,” or “Subkeys only.”
7. Under Access, select the actions that should be audited, and click OK.
If you need to enable auditing of the same Registry keys on multiple computers, a much
more efficient solution would be to use a GPO as follows:
1. Create a Group Policy Object (or modify an existing GPO) that enables the fol‐
lowing settings under Computer Configuration→Policies→Windows Set‐
tings→Security Settings→Local Policies→Audit Policy:
• Audit object access: Success
• Audit object access: Failure
2. Navigate to Computer Configuration→Policies→Windows Settings→Security Set‐
tings→Registry.
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3. Right-click on Registry and select “Add key.” On the “Select Registry key” screen,
navigate to the key that you want to audit and click OK.
4. Right-click on the key and select Permissions. Click Advanced and select the Au‐
diting tab.
5. Click Add to select a user or group to audit, then click OK. For Apply Onto, select
“This key only,” “This key and subkeys,” or “Subkeys only.”
6. Under Access, select the actions that should be audited, and click OK.
7. Link the GPO to the container containing the computers that you wish to audit.
The Advanced Audit Policy Configuration settings offer another way
to audit the Registry. This method allows you to use a global object
access audit policy, which provides for auditing without having to spec‐
ify security access control lists (SACLs). For additional information,
check out the “See Also” section of this recipe.
Discussion
Before you can enable auditing on specific Registry keys, you must create an audit policy
that enables auditing of object access events, both Success and Failure events. You can
enable auditing by modifying an existing GPO or by creating a new GPO created ex‐
pressly for this purpose. Maintaining a number of single-purpose GPOs can make for
easier Group Policy troubleshooting but can lead to performance implications if clients
need to process too many GPOs at logon and during the background refresh of Group
Policy. As is usually the case, the definition of “too many” will vary from one environ‐
ment to the next; it’s important to monitor the performance of your clients to determine
which approach is appropriate for your environment. Once you’ve enabled auditing of
a specific key or keys, information about the activity that you’ve chosen to audit will
appear in the Security event log of the computer where the event took place.
See Also
“Advanced Security Audit Policy Step-by-Step Guide”
15.15. Creating a Quota
Problem
You want to limit the number of objects a security principal can create in a partition by
creating a quota.
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Solution
Using a command-line interface
> dsadd quota -part <PartitionDN> -qlimit <QuotaLimit> -acct <PrincipalName>↵
[-rdn <QuotaName>]
The following command creates a quota specification that allows the ADATUM\rall‐
en user to create only five objects in the dc=adatum,dc=com partition:
> dsadd quota -part dc=adatum,dc=com -qlimit 5 -acct ADATUM\rallen
Discussion
Quotas allow an administrator to limit the number of objects that a user (or group of
users) can create. A quota applies not just to a user object, but also to the creation of
any object type in Active Directory. Three things need to be set when creating a quota
specification:
Partition
Currently, quotas can apply only to an entire partition. You cannot create a quota
that pertains only to a subtree in a partition. You can create quotas for any partition,
including application partitions, except for the schema naming context. The rea‐
soning behind this restriction is that the schema is a highly protected area of the
directory, and you shouldn’t need to restrict how many objects get created there.
Target security principal
A quota can be defined for any type of security principal. The msDSQuotaTrustee attribute on the quota object stores the target principal in the form
of an SID.
Limit
This determines how many objects the target security principal can create.
The quota limit is a combination of the new objects that a user creates plus any tomb‐
stone objects that are created by that user. If a user creates an object and then deletes
another object, that would still count as two objects toward any quotas that apply to the
user. This is because when an object is deleted, it isn’t removed; it is simply marked as
tombstoned. Once the tombstone object is removed from Active Directory, the user’s
quota will be decremented accordingly. By default, a tombstone object counts as one
object, but that is configurable. See Recipe 15.17 for more on changing the tombstone
quota factor.
Since quotas can be assigned to both users and groups, it is conceivable that multiple
quotas may apply to a user. In this case, the quota with the highest limit will be in force
for the user. You can also create a default quota for a partition that applies to all security
principals. See Recipe 15.18 for more information on configuring the default quota.
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Quotas do not apply to members of the Enterprise Admins and Domain
Admins groups. Even if you’ve configured a default quota for all users,
members of those administrative groups will not have any restrictions.
See Also
Recipe 8.13 for more on the computer object quota; this chapter’s Recipe 15.0 section
for more on the attributes of quota objects; Recipe 15.16 for finding the quotas assigned
to a security principal; Recipe 15.17 for changing the tombstone quota factor;
Recipe 15.18 for setting a default quota
15.16. Finding the Quotas Assigned to a Security Principal
Problem
You want to find the quotas that have been configured for a security principal (i.e., user,
group, or computer).
Solution
Using a command-line interface
> dsquery quota <PartitionDN> -acct <PrincipalName>
The following command searches for quotas that have been assigned to the ADATUM
\rallen user in the dc=adatum,dc=com partition:
> dsquery quota dc=adatum,dc=com -acct ADATUM\rallen
Using PowerShell
The following command searches for all quotas in a domain:
Get-ADObject -Filter {objectClass -eq "msDS-QuotaControl"} | FL Name
Discussion
The DSQuery solution will find only quotas that have been directly assigned to a security
principal; it will not list quotas that have been assigned to any group objects that the
principal may be a member of. The msDS-QuotaTrustee attribute on quota objects de‐
fines an SID that the quota applies to. The dsquery quota command will look up the
SID for the specified account and match that against quota objects that reference that
SID. Unfortunately, this doesn’t quite show the whole picture. A user could have a quota
assigned directly, which the DSQuery command would show, but the user could also
be part of one or more groups that have quotas assigned. These won’t show up using
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DSQuery. The PowerShell solution lists all quotas, including groups, for the Active
Directory domain. However, it does not show a relation between the user object and
any groups returned.
A more robust solution would entail retrieving the tokenGroups attribute of the user,
which contains a list of SIDs for all expanded group memberships, and then querying
each of those groups to determine whether any of them have quotas assigned. This is
actually the type of algorithm that is used to determine a user’s effective quota, as shown
in Recipe 15.19.
See Also
Recipe 15.15 for creating a quota; Recipe 15.19
15.17. Changing How Tombstone Objects Count Against
Quota Usage
Problem
You want to change the relative weight of tombstone objects in quota calculations.
Solution
Using a graphical user interface
1. Open ADSI Edit.
2. Connect to the partition on which you want to modify this setting. (This setting
must be changed for each partition that you want to configure.)
3. In the left pane, expand the root of the partition.
4. Right-click on cn=NTDS Quotas and select Properties.
5. Set the msDS-TombstoneQuotaFactor attribute to a value between 0 and 100.
6. Click OK.
Using a command-line interface
Create an LDIF file called change_ tombstone_quota.ldf with the following contents:
dn: cn=NTDS Quotas,<PartitionDN>
changetype: modify
replace: msDs-TombstoneQuotaFactor
msDs-TombstoneQuotaFactor: <1-100>
-
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Then run the following command:
> ldifde -v -i -f change_tombstone_quota.ldf
You can also make the change using DSMod or AdMod. DSMod takes the following
syntax:
> dsmod partition <PartitionDN> -qtmbstnwt <1-100>
You can make the change with AdMod, as follows:
> admod -b <PartitionDN> msDs-TombstoneQuotaFactor::<0-100>
Using PowerShell
You can modify the tombstone quota factor by using PowerShell, as follows:
Set-ADObject "<PartitionDN>" -Replace↵
@{"msDS-TombstoneQuotaFactor"="<QuotaValue>"}
Discussion
The tombstone quota factor is a percentage that determines how much each tombstone
object counts against a security principal’s quota usage. By default, tombstone objects
count as one object. This means if a user’s quota is set to 10 and the user deletes 10
objects, that user will not be able to create or delete any other objects until those tomb‐
stone objects have been purged from Active Directory.
The msDs-TombstoneQuotaFactor attribute on the NTDS Quota container for each par‐
tition defines the tombstone quota factor. As mentioned previously, the default is that
tombstone objects count 100 percent of a normal object; thus, the attribute msDsTombstoneQuotaFactor contains 100 by default. If you modify this attribute to contain
a value of 50 and a user has a quota limit of 10, then that user could delete a maximum
of 20 objects (i.e., create 20 tombstone objects) because 20 × 50 percent = 10. As another
example, you may not care about how many objects your users delete; in this case, you’d
want to set the tombstone quota factor to 0 so that tombstoned objects would not count
against a user’s NTDS quota at all.
See Also
MSDN: ms-DS-Tombstone-Quota-Factor attribute [AD Schema]; MSDN: ms-DSQuota-Container class [AD Schema]; “Active Directory Quotas”
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15.18. Setting the Default Quota for All Security Principals
in a Partition
Problem
You want to set a default quota for all security principals.
Solution
Using a graphical user interface
1. Open ADSI Edit.
2. Connect to the partition you want to modify. (This setting must be changed for
each partition that you want to configure.)
3. In the left pane, expand the root of the partition.
4. Right-click on cn=NTDS Quotas and select Properties.
5. Set the msDS-DefaultQuota attribute to the number of objects that security prin‐
cipals should be allowed to create if they are not assigned another quota.
6. Click OK.
Using a command-line interface
Create an LDIF file called set_default_quota.ldf with the following contents:
dn: cn=NTDS Quotas,<PartitionDN>
changetype: modify
replace: msDs-DefaultQuota
msDs-DefaultQuota: <NumberOfObjects>
-
Then run the following command:
> ldifde -v -i -f set_default_quota.ldf
You can also make the change using DSMod or AdMod. DSMod takes the following
syntax:
> dsmod partition <NTDS Quotas DN> -qdefault <DefaultQuota>
You can make the change with AdMod, as follows:
> admod -b <NTDS Quotas DN> msDs-DefaultQuota::<DefaultQuota>
Using PowerShell
You can modify the tombstone quota factor using PowerShell, as follows:
570 | Chapter 15: Logging, Monitoring, and Quotas
|
http://ter40.free.fr/ebooktmp/new/Active%20Directory%20Cookbook,%204th%20Edition.pdf
|
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