4.5.2. How FHRPs Work

The handoff process:

1. Active router sends hellos every 3 seconds (HSRP default)
2. Standby router listens. If it misses 3 hellos (hold time = 10 sec), it assumes active is dead
3. Standby becomes active, takes ownership of the VIP and virtual MAC
4. Standby sends gratuitous ARP to update switch MAC tables
5. Traffic now flows through the new active router

Key Concepts:

• Virtual IP (VIP): The gateway IP clients configure—shared between routers, never changes. Hosts must be given the VIP as their default gateway (statically or by DHCP), never a router's real address; a host pointed at a real address loses its gateway when that router fails, however the FHRP fails over
• Virtual MAC: A special MAC that moves with the VIP (so switches forward to the right router)
• Active/Master: The only router answering ARP for the VIP (with the virtual MAC) and forwarding traffic
• Standby/Backup: Monitoring, ready to take over
• Preemption: If enabled, a higher-priority router can reclaim active role after recovering
• Priority: HSRP uses 0–255, default 100; highest wins, and a tie goes to the highest interface IP
• HSRP states: Initial → Learn → Listen → Speak → Standby (next in line) → Active. Routers in Listen are neither active nor standby
• Tracking: standby 1 track <object> decrement 20 lowers priority when a tracked uplink fails, so a preempt-enabled peer takes over. VRRP, the open standard, uses the same priority (default 100) and tracking model, but unlike HSRP it preempts by default

Common configuration:

Router(config)# interface GigabitEthernet0/0
Router(config-if)# standby 1 ip 192.168.1.1          ! Virtual IP
Router(config-if)# standby 1 priority 110            ! Higher = more likely active
Router(config-if)# standby 1 preempt                 ! Take over if I have higher priority

⚠️ Exam Trap: HSRP and VRRP provide redundancy but not load balancing—all traffic goes through the active router while the standby sits idle. If you want both routers forwarding traffic, either use GLBP or create two HSRP groups (one where R1 is active for VLAN 10, another where R2 is active for VLAN 20).