Peer Dead Interval vs Delay Restore Timer in Cisco ACI

 

⏱️ 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.

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🔍 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.

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⏳ 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.

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🔄 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.