VRRP

The Problem of Default Gateway Redundancy

End hosts and servers are configured with a single default gatewayA network device (typically a router) that serves as the access point from a local network to other networks. The default gateway is the first hop for traffic destined outside the local subnet. IP address. If that router fails, all traffic from the subnet stops — even if a backup router is available. Virtual Router Redundancy Protocol (VRRP, RFC 5798) solves this by allowing multiple physical routers to share a virtual IP address and virtual MAC address, presenting themselves as a single logical router to the hosts on the segment.

Master and Backup Election

VRRP routers on a segment negotiate a Master role using priority values (1-254, default 100). The router with the highest priority becomes Master and owns the virtual IP and virtual MAC. Backup routers send no traffic but listen for VRRP advertisement multicast messages (224.0.0.18). If the Master fails to send advertisements within the advertisement interval (default 1 second) plus the master-down timer, the highest-priority Backup takes over the virtual IP within typically 3 seconds.

VRRP vs. HSRP

VRRP is an open IETF standard (RFC 5798), while HSRPHot Standby Router Protocol. A Cisco proprietary protocol that provides gateway redundancy by allowing multiple routers to share a virtual IP address. Similar in function to the open-standard VRRP. is a Cisco-proprietary protocol with similar functionality. Both achieve the same goal of first-hop router redundancy, but VRRP allows the virtual IP to match the Master's real interface IP, and VRRP version 3 adds native IPv6Internet Protocol version 6. The successor to IPv4 using 128-bit addresses (e.g., 2001:0db8::1), providing a virtually unlimited address space of 3.4 x 10^38 addresses. Designed to solve IPv4 address exhaustion. support. In multi-vendor environments, VRRP is preferred; Cisco-only shops often use HSRP for its additional features and Cisco support integration.