Walk through the three steps that occur during an FHRP router failover when the active router goes down.

Step 1: Standby stops receiving Hellos. Step 2: Standby assumes the forwarding role. Step 3: Standby takes over the virtual IP (Internet Protocol) and MAC (Media Access Control), so hosts see no disruption.

* The three-step FHRP (First Hop Redundancy Protocol) failover. *

Detailed failover sequence:

Step 1 — Failure detection:

• The active and standby routers exchange Hello messages at regular intervals (every 3 seconds for HSRP (Hot Standby Router Protocol))
• If the standby router stops receiving Hello messages from the active router, it starts a hold timer (default 10 seconds for HSRP)
• If no Hello arrives before the hold timer expires → the active router is declared dead

Step 2 — Role transition:

• The standby router assumes the role of the forwarding router
• It begins processing all traffic destined for the virtual IP/MAC
• If other routers are in the Listen state, a new standby is elected from among them

Step 3 — Transparent to hosts:

• The new active router takes over both the virtual IPv4 and virtual MAC addresses
• Host devices continue sending frames to the same virtual MAC → no ARP (Address Resolution Protocol) updates needed
• From the hosts' perspective: nothing changed — their default gateway still works

Failover time: With default HSRP timers, failover takes approximately 10 seconds (hold timer). This can be reduced to sub-second by tuning timers, but aggressive timers increase CPU load and risk false failovers.

Tip: Unlike STP (Spanning Tree Protocol) convergence (which can take 30-50 seconds), FHRP failover only affects the gateway — Layer 2 paths remain stable.

Go deeper:

• Hot Standby Router Protocol (Wikipedia) — the next-highest-priority router taking over the virtual MAC so hosts see no change.