Using VRRP in Your Network

Virtual Router Redundancy Protocol (VRRP) is an election protocol capable of dynamically assigning responsibility for a virtual router to one of the VRRP routers on a LAN. A virtual router is an abstract object managed by VRRP that acts as a default router for hosts on a shared LAN. It consists of a Virtual Router Identifier (VRID) and a set of associated IP addresses across a common LAN that define virtual router members. A VRRP router is a router with the VRRP protocol running on it. A VRRP router may participate in and backup one or more virtual routers.

VRRP specifies an election protocol that dynamically assigns responsibility for a virtual router to one of the VRRP routers on a LAN. The elected VRRP router is called the master. The router master controls the IP addresses associated with a virtual router. The master forwards packets sent to these IP addresses. The VRRP election process provides dynamic fail over of forwarding responsibility to another VRRP router should the current master become unavailable. This allows any of the virtual router IP addresses on the LAN to be used as the default first hop router by end-hosts. In this way, VRRP provides a higher availability default path without requiring configuration of dynamic routing or router discovery protocols on every end-host.

Note

When configuring an IPv6 VRRP link local address, all link local addresses must match on all routers running the same VRRP instance in a LAN segment. Only one link local address on a VRRP instance will be active at any given time.

Statically configured default routes can represent a single point of failure that can result in a catastrophic event, isolating all end-hosts that are unable to detect any alternate available path. VRRP is designed to eliminate the single point of failure inherent in the static default routed environment.

A critical-IP address defines an interface that will prevent the master router from functioning properly if the interface were to fail. When a critical IP interface goes down, its operational priority can be set to decrement to a value lower than the priority set for the backup router. In this case, the backup router becomes the master.

Fabric route mode can be enabled on the VRRP router allowing a VRRP instance in the backup state to forward IPv4 and IPv6 packets destined for the VRRP MAC address