diff --git a/Documentation/faq.md b/Documentation/faq.md
index 3223d018c..bfa47e256 100644
--- a/Documentation/faq.md
+++ b/Documentation/faq.md
@@ -92,6 +92,12 @@ A slow network can also cause this issue. If network metrics among the etcd mach
 
 If none of the above suggestions clear the warnings, please [open an issue][new_issue] with detailed logging, monitoring, metrics and optionally workload information.
 
+#### What does the etcd warning "request ignored (cluster ID mismatch)" mean?
+
+Every new etcd cluster generates a new cluster ID based on the initial cluster configuration and a user-provided unique `initial-cluster-token` value. By having unique cluster ID's, etcd is protected from cross-cluster interaction which could corrupt the cluster.
+
+Usually this warning happens after tearing down an old cluster, then reusing some of the peer addresses for the new cluster. If any etcd process from the old cluster is still running it will try to contact the new cluster. The new cluster will recognize a cluster ID mismatch, then ignore the request and emit this warning. This warning is often cleared by ensuring peer addresses among distinct clusters are disjoint.
+
 [hardware-setup]: ./op-guide/hardware.md
 [supported-platform]: ./op-guide/supported-platform.md
 [wal_fsync_duration_seconds]: ./metrics.md#disk