connect.c is a simple relaying command to make network connection +via SOCKS and https proxy. It is mainly intended to be used as proxy +command of OpenSSH. You can make SSH session beyond the firewall with +this command,
Features of connect.c are:
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+
-
+
+Supports SOCKS (version 4/4a/5) and https CONNECT method. +
+
+ -
+
+Supports NO-AUTH and USERPASS authentication of SOCKS5 +
+
+ -
+
+You can input password from tty, ssh-askpass or environment variable. +
+
+ -
+
+Run on UNIX or Windows platform. +
+
+ -
+
+You can compile with various C compiler (cc, gcc, Visual C, Borland C. etc.) +
+
+ -
+
+Simple and general program independent from OpenSSH. +
+
+ -
+
+You can also relay local socket stream instead of standard I/O. +
+
+
You can download source code +(connect.c) +on the project page.
Pre-compiled binary for MS Windows is also available on +download page.
What is proxy command?
+OpenSSH development team decides to stop supporting SOCKS and any +other tunneling mechanism. It was aimed to separate complexity to +support various mechanism of proxying from core code. And they +recommends more flexible mechanism: ProxyCommand option instead.
Proxy command mechanism is delegation of network stream +communication. If ProxyCommand options is specified, SSH invoke +specified external command and talk with standard I/O of thid +command. Invoked command undertakes network communication with +relaying to/from standard input/output including iniitial +communication or negotiation for proxying. Thus, ssh can split out +proxying code into external command.
The connect.c program was made for this purpose.
How to Use
+Get Source
+You can get source code from project download page. +Pre-compiled MS Windows binary is also available there.
Compile and Install
+In most environment, you can compile connect.c simply. On UNIX +environment, you can use cc or gcc. On Windows environment, you can +use Microsoft Visual C, Borland C or Cygwin gcc.
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+
- +UNIX cc + +
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+
+cc connect.c -o connect +
+
+ - +UNIX gcc + +
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+
+gcc connect.c -o connect +
+
+ - +Solaris + +
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+
+gcc connect.c -o connect -lnsl -lsocket -lresolv +
+
+ - +Microsoft Visual C/C++ + +
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+
+cl connect.c wsock32.lib advapi32.lib +
+
+ - +Borland C + +
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+
+bcc32 connect.c wsock32.lib advapi32.lib +
+
+ - +Cygwin gcc + +
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+
+gcc connect.c -o connect +
+
+ - +Mac OS/Darwin + +
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+
+gcc connect.c -o connect -lresolv +
+
+
To install connect command, simply copy compiled binary to directory +in your PATH (ex. /usr/local/bin). Like this:
$ cp connect /usr/local/bin+
Modify your ~/.ssh/config
+Modify your ~/.ssh/config file to use connect command as proxy +command. For the case of SOCKS server is running on firewall host +socks.local.net with port 1080, you can add ProxyCommand option in +~/.ssh/config, like this:
Host remote.outside.net + ProxyCommand connect -S socks.local.net %h %p+
%h and %p will be replaced on invoking proxy command with target +hostname and port specified to SSH command.
If you hate writing many entries of remote hosts, following example +may help you.
## Outside of the firewall, use connect command with SOCKS conenction. +Host * + ProxyCommand connect -S socks.local.net %h %p + +## Inside of the firewall, use connect command with direct connection. +Host *.local.net + ProxyCommand connect %h %p+
If you want to use http proxy, use -H option instead of -S option +in examle above, like this:
## Outside of the firewall, with HTTP proxy +Host * + ProxyCommand connect -H proxy.local.net:8080 %h %p + +## Inside of the firewall, direct +Host *.local.net + ProxyCommand connect %h %p+
Use SSH
+After editing your ~/.ssh/config file, you are ready to use ssh. You +can execute ssh without any special options as if remote host is IP +reachable host. Following is an example to execute hostname command on +host remote.outside.net.
local$ ssh remote.outside.net hostname +Hello, this is remote.outside.net +remote$+
Have trouble?
+If you have trouble, execute connect command from command line with -d +option to see what is happened. Some debug message may appear and +reports progress. This information may tell you what is wrong. In this +example, error has occurred on authentication stage of SOCKS5 +protocol.
$ connect -d -S socks.local.net unknown.remote.outside.net 110 +DEBUG: relay_method = SOCKS (2) +DEBUG: relay_host=socks.local.net +DEBUG: relay_port=1080 +DEBUG: relay_user=gotoh +DEBUG: socks_version=5 +DEBUG: socks_resolve=REMOTE (2) +DEBUG: local_type=stdio +DEBUG: dest_host=unknown.remote.outside.net +DEBUG: dest_port=110 +DEBUG: Program is $Revision: 1.20 $ +DEBUG: connecting to xxx.xxx.xxx.xxx:1080 +DEBUG: begin_socks_relay() +DEBUG: atomic_out() [4 bytes] +DEBUG: >>> 05 02 00 02 +DEBUG: atomic_in() [2 bytes] +DEBUG: <<< 05 02 +DEBUG: auth method: USERPASS +DEBUG: atomic_out() [some bytes] +DEBUG: >>> xx xx xx xx ... +DEBUG: atomic_in() [2 bytes] +DEBUG: <<< 01 01 +ERROR: Authentication faield. +FATAL: failed to begin relaying via SOCKS.+
More Detail
+Command line usage is here:
usage: connect [-dnhs45] [-R resolve] [-p local-port] [-w sec] + [-H [user@]proxy-server[:port]] + [-S [user@]socks-server[:port]] + host port+
host and port is target hostname and port-number to connect.
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+
- +-H [user@]server[:port] + +
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+
+ Specify hostname and port number of http proxy server to + relay. If port is omitted, 80 is used. +
+
+ - +-h + +
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+
+ Use HTTP proxy via proxy server sepcified by environment variable + HTTP_PROXY. +
+
+ - +-S [_user_@]server\[:_port_] + +
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+
+ Specify hostname and port number of SOCKS server to + relay. Like -H option, port number can be omit and default is 1080. +
+
+ - +-s + +
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+
+ Use SOCKS proxy via SOCKS server sepcified by environment variable + SOCKS5_SERVER. +
+
+ - +-4 + +
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+
+Use SOCKS version 4 protocol. + This option must be used with -S. +
+
+ - +-5 + +
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+
+Use SOCKS version 5 protocol. + This option must be used with -S. +
+
+ - +-R method + +
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+
+The method to resolve hostname. 3 keywords (local, + remote, both) or dot-notation IP address is allowed. Keyword + both means; "Try local first, then remote". If dot-notation IP + address is specified, use this host as nameserver (UNIX + only). Default is remote for SOCKS5 or local for others. On SOCKS4 + protocol, remote resolving method (remote and both) use protocol + version 4a. +
+
+ - +-p port + +
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+
+Accept on local TCP port and relay it instead of standard input +and output. With this option, program will terminate when remote or +local TCP session is closed. +
+
+ - +-w timeout + +
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+
+Timeout seconds for connecting to remote host. +
+
+ - +-a auth + +
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+
+option specifiys user intended authentication methods +separated by comma. Currently userpass and none are +supported. Default is userpass. You can also specifying this parameter +by the environment variable SOCKS5_AUTH. +
+
+
-d: Run with debug message output. If you fail to connect, use this +option to see what is done.
As additional feature, +you can omit port argument when program name is special format +containing port number itself like "connect-25". For example:
$ ln -s connect connect-25 +$ ./connect-25 smtphost.outside.net +220 smtphost.outside.net ESMTP Sendmail +QUIT +221 2.0.0 smtphost.remote.net closing connection +$+
This example means that the command name "connect-25" indicates port +number 25 so you can omit 2nd argument (and used if specified +explicitly). +This is usefull for the application which invokes only with hostname +argument.
Specifying user name via environment variables
+There are 5 environemnt variables to specify user name without command +line option. This mechanism is usefull for the user who using another +user name different from system account.
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+
- +SOCKS5_USER + +
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+
+ Used for SOCKS v5 access. +
+
+ - +SOCKS4_USER + +
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+
+ Used for SOCKS v4 access. +
+
+ - +SOCKS_USER + +
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+
+ Used for SOCKS v5 or v4 access and varaibles above are not defined. +
+
+ - +HTTP_PROXY_USER + +
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+
+ Used for HTTP proxy access. +
+
+ - +CONNECT_USER + +
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+
+ Used for all type of access if all above are not defined. +
+
+
Following table describes how user name is determined. Left most number is order to check. If variable is not defined, check next variable, and so on.
| + | SOCKS v5 |
+SOCKS v4 |
+HTTP proxy |
+
1 |
+SOCKS5_USER |
+SOCKS4_USER |
+HTTP_PROXY_USER |
+
2 |
+SOCKS_USER |
+||
3 |
+CONNECT_USER |
+||
4 |
+(query user name to system) |
+||
Specifying password via environment variables
+There are 5 environemnt variables to specify password. If you use this +feature, please note that it is not secure way.
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+
- +SOCKS5_PASSWD + +
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+
+ Used for SOCKS v5 access. This variables is compatible with NEC SOCKS implementation. +
+
+ - +SOCKS5_PASSWORD + +
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+
+ Used for SOCKS v5 access if SOCKS5_PASSWD is not defined. +
+
+ - +SOCKS_PASSWORD + +
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+
+ Used for SOCKS v5 (or v4) access all above is not defined. +
+
+ - +HTTP_PROXY_PASSWORD + +
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+
+ Used for HTTP proxy access. +
+
+ - +CONNECT_PASSWORD + +
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+
+ Used for all type of access if all above are not defined. +
+
+
Following table describes how password is determined. Left most number +is order to check. If variable is not defined, check next variable, +and so on. Finally ask to user interactively using external program or +tty input.
| + | SOCKS v5 |
+HTTP proxy |
+
1 |
+SOCKS5_PASSWD |
+HTTP_PROXY_PASSWORD |
+
2 |
+SOCKS_PASSWORD |
+|
3 |
+CONNECT_PASSWORD |
+|
4 |
+(ask to user interactively) |
+|
Limitations
+SOCKS5 authentication
+Only NO-AUTH and USER/PASSWORD authentications are supported. GSSAPI +authentication (RFC 1961) and other draft authentications (CHAP, EAP, +MAF, etc.) is not supported.
HTTP authentication
+BASIC authentication is supported but DIGEST authentication is not.
Switching proxy server on event
+There is no mechanism to switch proxy server regarding to PC +environment. This limitation might be bad news for mobile user. Since +I do not want to make this program complex, I do not want to support +although this feature is already requested. Please advice me if there +is good idea of detecting environment to swich and simple way to +specify conditioned directive of servers.
One tricky workaround exists. It is replacing ~/.ssh/config file by +script on ppp up/down.
There’s another example of wrapper script (contributed by Darren +Tucker). This script costs executing ifconfig and grep to detect +current environment, but it works. Note that you should modify +addresses if you use it.
#!/bin/sh +## ~/bin/myconnect --- Proxy server switching wrapper + +if ifconfig eth0 |grep "inet addr:192\.168\.1" >/dev/null; then + opts="-S 192.168.1.1:1080" +elif ifconfig eth0 |grep "inet addr:10\." >/dev/null; then + opts="-H 10.1.1.1:80" +else + opts="-s" +fi +exec /usr/local/bin/connect $opts $@+
Tips
+Proxying socket connection
+In usual, connect.c relays network connection to/from standard +input/output. By specifying -p option, however, connect.c relays local +network stream instead of standard input/output. With this option, +connect command waits connection from other program, then start +relaying between both network stream.
This feature may be useful for the program which is hard to SOCKSify.
Use with ssh-askpass command
+connect.c ask you password when authentication is required. If you +are using on tty/pty terminal, connect can input from terminal with +prompt. But you can also use ssh-askpass program to input password. If +you are graphical environment like X Window or MS Windows, and program +does not have tty/pty, and environment variable SSH_ASKPASS is +specified, then connect.c invoke command specified by environment +variable SSH_ASKPASS to input password. ssh-askpass program might be +installed if you are using OpenSSH on UNIX environment. On Windows +environment, pre-compiled binary is available from here.
This feature is limited on window system environment.
And also useful on Emacs on MS Windows (NT Emacs or Meadow). It is +hard to send passphrase to connect command (and also ssh) because +external command is invoked on hidden terminal and do I/O with this +terminal. Using ssh-askpass avoids this problem.
Use for Network Stream of Emacs
+Although connect.c is made for OpenSSH, it is generic and independent +from OpenSSH. So we can use this for other purpose. For example, you +can use this command in Emacs to open network connection with remote +host over the firewall via SOCKS or HTTP proxy without SOCKSifying +Emacs itself.
There is sample code: +http://bitbucket.org/gotoh/connect/src/tip/relay.el
With this code, you can use relay-open-network-stream function instead +of open-network-stream to make network connection. See top comments of +the source for more detail.
Remote resolver
+If you are SOCKS4 user on UNIX environment, you might want specify +nameserver to resolve remote hostname. You can do it specifying -R +option followed by IP address of resolver.
Hopping Connection via SSH
+Conbination of ssh and connect command have more interesting +usage. Following command makes indirect connection to host2:port from +your current host via host1.
$ ssh host1 connect host2 port+
This method is useful for the situations like:
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+
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+
+You are outside of organizasion now, but you want to access an + internal host barriered by firewall. +
+
+ -
+
+You want to use some service which is allowed only from some limited hosts. +
+
+
For example, I want to use local NetNews service in my office from +home. I cannot make NNTP session directly because NNTP host is +barriered by firewall. Fortunately, I have ssh account on internal +host and allowed using SOCKS5 on firewall from outside. So I use +following command to connect to NNTP service.
$ ssh host1 connect news 119 +200 news.my-office.com InterNetNews NNRP server INN 2.3.2 ready (posting ok). +quit +205 . +$+
By combinating hopping connection and relay.el, I can read NetNews +using Wanderlust on Emacs at home.
| + External (internet) | Internal (office) + | ++------+ +----------+ +-------+ +-----------+ +| HOME | | firewall | | host1 | | NNTP host | ++------+ +----------+ +-------+ +-----------+ + emacs <-------------- ssh ---------------> sshd <-- connect --> nntpd + <-- connect --> socksd <-- SOCKS -->+
As an advanced example, you can use SSH hopping as fetchmail’s plug-in +program to access via secure tunnel. This method requires that connect +program is insatalled on remote host. There’s example of .fetchmailrc +bellow. When fetchmail access to mail-server, you will login to remote +host using SSH then execute connect program on remote host to relay +conversation with pop server. Thus fetchmail can retrieve mails in +secure.
poll mail-server + protocol pop3 + plugin "ssh %h connect localhost %p" + username "username" + password "password"+
Break The More Restricted Wall
+If firewall does not provide SOCKS nor HTTPS other than port 443, you +cannot break the wall in usual way. But if you have you own host which +is accessible from internet, you can make ssh connection to your own +host by configuring sshd as waiting at port 443 instead of standard +22. By this, you can login to your own host via port 443. Once you +have logged-in to extenal home machine, you can execute connect as +second hop to make connection from your own host to final target host, +like this:
internal$ cat ~/.ssh/config +Host home + ProxyCommand connect -H firewall:8080 %h 443 + +Host server # internal + ProxyCommand ssh home connect %h %p + +internal$ ssh home +You are logged in to home! +home# exit +internal$ ssh server +You are logged in to server! +server# exit +internal$+
This way is similar to "Hopping connection via SSH" except configuring +outer sshd as waiting at port 443 (https). This means that you have a +capability to break the strongly restricted wall if you have own host +out side of the wall.
| + Internal (office) | External (internet) + | ++--------+ +----------+ +------+ +--------+ +| office | | firewall | | home | | server | ++--------+ +----------+ +------+ +--------+ + <------------------ ssh --------------------->sshd:443 + <-- connect --> http-proxy <-- https:443 --> any + connect <-- tcp --> port+
|
+ Note
+ |
+If you wanna use this, you should give up hosting https + service at port 443 on you external host home. | +
F.Y.I.
+Difference between SOCKS versions
+SOCKS version 4 is first popular implementation which is documented +here. Since this +protocol provide IP address based requesting, client program should +resolve name of outer host by itself. Version 4a (documented +here) is +enhanced to allow request by hostname instead of IP address.
SOCKS version 5 is re-designed protocol stands on experience of +version 4 and 4a. There is no compativility with previous +versions. Instead, there’s some improvement: IPv6 support, request by +hostname, UDP proxying, etc.
Configuration to use HTTPS
+Many http proxy servers implementation supports https CONNECT method +(SLL). You might add configuration to allow using https. For the +example of DeleGate (DeleGate is a +multi-purpose application level gateway, or a proxy server) , you +should add https to REMITTABLE parameter to allow HTTP-Proxy like +this:
delegated -Pxxxx ...... REMITTABLE='+,https' ...+
For the case of Squid, you should allow target ports via https by ACL, +and so on.
SOCKS5 Servers
+-
+
- +NEC SOCKS Reference Implementation + +
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+
+ Reference implementation of SOKCS server and library. +
+
+ - +Dante + +
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+
+ Dante is free implementation of SOKCS server and library. Many + enhancements and modulalized. +
+
+ - +DeleGate + +
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+
+ DeleGate is multi function proxy service provider. DeleGate 5.x.x + or earlier can be SOCKS4 server, and 6.x.x can be SOCKS5 and + SOCKS4 server. and 7.7.0 or later can be SOCKS5 and SOCKS4a + server. +
+
+
Specifications
+-
+
- +socks4.protocol.txt + +
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+
+ SOCKS: A protocol for TCP proxy across firewalls +
+
+ - +socks4a.protocol.txt + +
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+
+ SOCKS 4A: A Simple Extension to SOCKS 4 Protocol +
+
+ - +RFC 1928 + +
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+
+ SOCKS Protocol Version 5 +
+
+ - +RFC 1929 + +
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+
+ Username/Password Authentication for SOCKS V5 +
+
+ - +RFC 2616 + +
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+
+ Hypertext Transfer Protocol — HTTP/1.1 +
+
+ - +RFC 2617 + +
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+
+ HTTP Authentication: Basic and Digest Access Authentication +
+
+
Related Links
+-
+
-
+
+OpenSSH Home +
+
+ - + + +
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+
+Using OpenSSH through a SOCKS compatible PROXY on your LAN (J. Grant) +
+
+
Similars
+-
+
- +Proxy Tunnel + +
-
+
+Proxying command using https CONNECT. +
+
+ - +stunnel + +
-
+
+Proxy through an https tunnel (Perl script) +
+
+