Reference Solution
Step 1 — Identify the degraded node
nodetool status
# → node1 (10.10.1.2) shows DN (Down/Normal)
Step 2 — Diagnose: cluster NIC is down
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
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
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.
ssh node1 nodetool repair bench
# Wait for: "Repair completed successfully"
Step 6 — Verify consistency
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.