⏱️ Peer Dead Interval vs Delay Restore Timer in
Cisco ACI: Timing the Trust
In Cisco ACI, timing
is everything — especially when it comes to maintaining stable vPC (Virtual
Port Channel) peer relationships. Two critical timers help manage how ACI
reacts to peer disruptions and recoveries: Peer Dead Interval and Delay
Restore Timer. Though they sound similar, they serve very different
purposes.
🔍 Peer Dead Interval: Watching for Silence
Think of the Peer
Dead Interval as a watchdog timer. It defines how long a switch should
wait before declaring its vPC peer as dead — meaning
unreachable or non-responsive.
- Purpose: Detect peer failure.
- Trigger: Lack of heartbeat (keepalive) messages.
- Default: Typically 3.5 seconds in ACI.
- Impact: If the peer is declared dead, the switch may take over certain
roles or shut down vPC member ports to avoid split-brain scenarios.
🧠 Analogy: It’s like waiting for a
friend to reply to your message. If they don’t respond within a few seconds,
you assume something’s wrong.
⏳ Delay Restore Timer: Holding Back the Comeback
The Delay
Restore Timer is used after a peer recovers. It
delays the reactivation of vPC member ports or SVIs (Switched Virtual
Interfaces) on the recovering switch.
- Purpose: Prevent flapping and ensure stable reconvergence.
- Trigger: Peer switch reboot or recovery.
- Default: 10 seconds (can be customized).
- Impact: Gives time for control plane protocols (like STP, routing) to
settle before data plane resumes.
🧠 Analogy: It’s like giving your
friend a moment to catch their breath after they’ve returned from a sprint —
before asking them to jump back into a conversation.
🔄 Why Both Matter
Together, these timers
ensure that:
- ACI doesn’t overreact to
temporary glitches. - Recovery is graceful, avoiding
packet loss or loops. - Network stability is maintained even
during failures and reboots.