First-Hop Redundancy Protocols hand hosts one virtual gateway (VIP + virtual MAC) backed by several routers. Pick by environment:
Cisco-only + simple → HSRP · multivendor → VRRP · active load balancing → GLBP
| HSRP | VRRP | GLBP | |
|---|---|---|---|
| Standard | Cisco | RFC 5798 | Cisco |
| Roles | Active / Standby | Master / Backup | AVG / AVF |
| Transport | UDP 1985 | IP proto 112 | UDP 3222 |
| Multicast | 224.0.0.2 (v2 .102) | 224.0.0.18 | 224.0.0.102 |
| Virtual MAC | 0000.0c07.acXX | 0000.5e00.01XX | several |
| Timers | 3/10 s | 1 s | 3/10 s |
Universal failure table: wrong router active → priority; no failover → group-ID mismatch or missing preempt; flapping → mismatched timers; traffic dies with an uplink → missing tracking.