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02dd0fd | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 | # Reference Solution
## Step 1 — Identify the degraded node
```bash
nodetool status
# → node1 (10.10.1.2) shows DN (Down/Normal)
```
## Step 2 — Diagnose: cluster NIC is down
```bash
ssh node1 ip link show enp6s0f1
# → state DOWN — the cluster-internal NIC is offline
```
The management NIC (`enp1s0f0`) is still up (SSH works), but node1 lost its cluster gossip link on `enp6s0f1`.
## Step 3 — Restore the NIC
```bash
ssh node1 sudo ip link set enp6s0f1 up
```
Cassandra gossip will detect the NIC coming back and automatically mark node1 as UN within ~30–60 seconds.
## Step 4 — Confirm node rejoined
```bash
nodetool status
# → All 3 nodes UN
```
## Step 5 — Repair stale data
While node1 was isolated, writes at QUORUM consistency went to node0 and node2. node1 missed those mutations.
```bash
ssh node1 nodetool repair bench
# Wait for: "Repair completed successfully"
```
## Step 6 — Verify consistency
```bash
cqlsh 10.10.1.2 -e "CONSISTENCY ONE; SELECT * FROM bench.kv;"
# → Should show 5 rows (ids 1–5, including delta and epsilon written during outage)
```
## Root Cause Summary
Physical NIC failure on node1's cluster interface (`enp6s0f1`) caused the node to become unreachable on the Cassandra gossip/storage network (10.10.1.x). The node continued to function (OS up, management SSH accessible) but was invisible to the cluster. Writes at QUORUM consistency proceeded with 2/3 replicas (node0 + node2), leaving node1 with a stale copy. Bringing the NIC back up restores gossip, and `nodetool repair` performs Merkle-tree-based anti-entropy sync to reconcile the divergent data.
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