3.6 First Hop Redundancy Protocols (FHRP)
Key Takeaways
- FHRPs provide gateway redundancy so that if the default gateway router fails, another takes over transparently.
- HSRP (Cisco proprietary) uses an active/standby model with a virtual IP and virtual MAC address.
- VRRP (IEEE standard) uses a master/backup model similar to HSRP but is vendor-neutral.
- GLBP (Cisco proprietary) provides both gateway redundancy and load balancing across multiple routers.
- The CCNA tests FHRP concepts only—not detailed configuration.
First Hop Redundancy Protocols (FHRP)
The Problem FHRPs Solve
End devices (PCs, phones) are configured with a single default gateway IP address. If that gateway router fails, all devices using it lose connectivity to other networks—even if another router on the same subnet is available.
FHRPs solve this by creating a virtual IP address (VIP) shared between two or more routers. If the active router fails, another router takes over the VIP seamlessly. End devices don't need to be reconfigured—they continue sending traffic to the same VIP.
HSRP (Hot Standby Router Protocol)
| Feature | Detail |
|---|---|
| Standard | Cisco proprietary |
| Model | Active / Standby |
| Virtual IP | Configured by administrator |
| Virtual MAC | 0000.0c07.acXX (XX = group number in hex) |
| Multicast | 224.0.0.2 (v1) or 224.0.0.102 (v2) |
| Hello timer | 3 seconds (default) |
| Hold timer | 10 seconds (default) |
| Preemption | Disabled by default (must be enabled) |
| Versions | HSRPv1 (groups 0-255), HSRPv2 (groups 0-4095) |
HSRP States
| State | Description |
|---|---|
| Initial | HSRP is starting |
| Learn | Router hasn't determined VIP |
| Listen | Router knows VIP but is not active or standby |
| Speak | Router is sending Hello and participating in election |
| Standby | Backup router, ready to take over |
| Active | Currently forwarding traffic for the VIP |
HSRP Election
- Highest priority becomes Active (default priority = 100)
- If priorities tie, highest IP address wins
- Preemption must be enabled for a higher-priority router to take over from a lower-priority Active router
VRRP (Virtual Router Redundancy Protocol)
| Feature | Detail |
|---|---|
| Standard | IEEE (RFC 5798) — vendor-neutral |
| Model | Master / Backup |
| Virtual IP | Can be the same as the Master's real IP |
| Virtual MAC | 0000.5e00.01XX (XX = group number) |
| Preemption | Enabled by default |
VRRP is functionally similar to HSRP but is an open standard, making it interoperable across different vendors.
GLBP (Gateway Load Balancing Protocol)
| Feature | Detail |
|---|---|
| Standard | Cisco proprietary |
| Model | AVG (Active Virtual Gateway) + AVFs (Active Virtual Forwarders) |
| Key advantage | Load balancing across multiple routers |
| Virtual MAC | Multiple (one per AVF): 0007.b400.XXYY |
How GLBP is unique: While HSRP and VRRP only use one active router (the other sits idle), GLBP distributes traffic across multiple routers. The AVG assigns different virtual MAC addresses to different clients, spreading the load.
FHRP Comparison
| Feature | HSRP | VRRP | GLBP |
|---|---|---|---|
| Standard | Cisco | IEEE | Cisco |
| Active router | 1 | 1 | Multiple |
| Load balancing | No | No | Yes |
| Preemption default | Off | On | Off |
| Virtual MAC | 0000.0c07.acXX | 0000.5e00.01XX | 0007.b400.XXYY |
On the Exam: The CCNA tests FHRP concepts, not detailed configuration. Know the purpose (gateway redundancy), the three protocols and their differences, and that HSRP is Cisco-proprietary while VRRP is IEEE standard. GLBP adds load balancing.
What is the primary purpose of First Hop Redundancy Protocols (FHRPs)?
Which FHRP is an open IEEE standard (vendor-neutral)?
Which FHRP provides both gateway redundancy AND active load balancing across multiple routers?