FHRP (First Hop Redundancy Protocol) is a family of protocols – HSRP, VRRP and GLBP – that maintain network continuity by assigning a virtual IP and MAC address to several routers. One router is active, the others standby; on failure a standby takes over automatically, giving higher availability.
Rule of thumb: Cisco-only + simple → HSRP · multivendor → VRRP · automatic load balancing → GLBP.
Comparison
| Topic | HSRP | VRRP | GLBP |
|---|---|---|---|
| Standard | Cisco proprietary | Open standard (RFC 5798) | Cisco proprietary |
| OSI layer | Layer 3 | Layer 3 | Layer 3 |
| Multicast address | 224.0.0.2 | 224.0.0.18 | 224.0.0.102 |
| Transport | UDP 1985 | IP protocol 112 | UDP 3222 |
| Virtual IP | 1 per group | 1 per group | 1 per group |
| Virtual MAC | 0000.0c07.acXX |
0000.5e00.01XX |
Multiple virtual MACs |
| Roles | Active / Standby | Master / Backup | AVG / AVF |
| Default priority | 100 (0–255) | 100 (0–255) | 100 (0–255) |
| Timers | 3 s / 10 s | 1 s | 3 s / 10 s |
| Versions | v1, v2 | v2, v3 | – |
Who is who?
- HSRP: Cisco proprietary, classic Active/Standby, most used in Cisco environments
- VRRP: open standard, Master/Backup, multivendor networks
- GLBP: Cisco proprietary, AVG/AVF, multiple virtual MAC addresses
Troubleshooting table
| Problem / symptom | Likely cause | Check / solution |
|---|---|---|
| Clients lose the gateway on router failure | FHRP not active | Check FHRP config on both devices |
| No Active/Master elected | Different FHRP groups | Check group ID |
| Wrong router is Active | Higher priority on the “wrong” device | Check priority |
| Expected router doesn’t take over | Preemption off | Check preempt |
| Flapping Active/Master | Mismatched timers | Compare hello/hold timers |
| Clients can’t reach the gateway | Wrong virtual IP | Check virtual IP on both |
| FHRP state Init/Listen | Interface down | Check interface status |
| Traffic stops on link failure | Missing tracking | Check tracking |
| Multicast not received | ACL blocking | Check ACLs |
| Unstable after reload | Router doesn’t win back control | Check preemption + priority |
Verification commands
show standby
show vrrp
show glbp
show ip interface brief
show running-configQuick troubleshooting
No failover?
→ check group
→ check priority
→ check preemption
→ check timers