March 2012 | 9 min read
High Availability is critical in enterprise networks. First Hop Redundancy Protocols (FHRPs) ensure gateway continuity if a router fails, allowing end hosts to maintain connectivity. In 2012, network engineers widely adopted three main FHRP standards: HSRP, VRRP, and GLBP.
Why FHRP Matters
End devices typically configure a single default gateway. If that router goes offline, those devices are stranded. FHRPs introduce a virtual IP and MAC address shared among routers in a group, enabling seamless failover without manual intervention.
HSRP: Hot Standby Router Protocol
Developed by Cisco, HSRP is proprietary and heavily deployed in Cisco-based networks. In an HSRP group, routers elect an Active and Standby router. The Active router handles traffic, while the Standby monitors it and takes over if it fails.
Key Features
- Virtual IP and MAC address
- Default hello timer: 3s, hold: 10s
- Supports preemption and authentication
- Version 1 (IPv4 only) and Version 2 (adds IPv6 support)
Use Case
In dual-router edge designs, HSRP provides deterministic failover behavior. By tuning priorities and enabling preemption, you can control which router is primary.
VRRP: Virtual Router Redundancy Protocol
VRRP is an open standard (RFC 3768) with similar functionality to HSRP. It allows multiple vendors to implement redundancy. In a VRRP group, the Master router responds to ARP requests for the virtual IP. Backup routers remain passive unless the Master fails.
Key Features
- Supports multiple vendors (open standard)
- Virtual IP must match real IP on Master router
- Default hello interval: 1s
- No need to configure a virtual MAC (standardized)
Use Case
When multi-vendor gear is used or standards compliance is essential, VRRP is the preferred choice. It's also used when licensing constraints make proprietary protocols less feasible.
GLBP: Gateway Load Balancing Protocol
GLBP, another Cisco innovation, adds load balancing to gateway redundancy. Instead of a single active router, GLBP elects an Active Virtual Gateway (AVG) and assigns multiple Active Virtual Forwarders (AVFs). Each end host gets a different virtual MAC, enabling real-time load sharing.
Key Features
- Redundancy plus load balancing
- Each router can actively forward traffic
- Supports up to 4 AVFs per group
- Configurable weighting for traffic distribution
Use Case
In environments where both bandwidth utilization and redundancy matter, GLBP is ideal. Especially useful in LANs with large user populations or VoIP deployments.
Comparative Summary
| Feature | HSRP | VRRP | GLBP |
|---|---|---|---|
| Standard | Cisco Proprietary | RFC (Open) | Cisco Proprietary |
| Load Balancing | No | No | Yes |
| Active Routers | 1 | 1 | Multiple |
| IPv6 Support | HSRPv2 | VRRPv3 | Limited |
Best Practices
- Use preemption carefully; avoid flapping
- Always monitor interface tracking and failover behavior
- For VoIP networks, GLBP can avoid jitter by balancing outbound links
- Validate FHRP compatibility with firewalls and NAT devices
Conclusion
FHRPs remain essential for resilient network design. Understanding the strengths and limitations of HSRP, VRRP, and GLBP empowers engineers to make informed decisions based on vendor choice, performance needs, and compatibility.
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