Virtual Router Redundancy Protocol (VRRP) Feature Overview and Configuration Guide

This guide describes the Virtual Router Redundancy Protocol (VRRP) feature provided by AlliedWare Plus devices, and how to configure devices to participate in a virtual router. Devices can be Layer 3 switches or firewalls.

One function of a device is to act as a gateway to the WAN for hosts on a LAN. On larger LANs, two or more devices may act as the gateway, and hosts use a dynamic routing protocol, such as RIP or OSPF, to determine the gateway device to use as the next hop in order to reach a specific IP destination. However, there are a number of factors, such as administrative or processing overhead or even support for the protocols, which may make it undesirable to use a dynamic routing protocol. One alternative is to use static routing; however, if the statically configured first hop device fails, the hosts on the LAN are unable to communicate with those on the WAN.

The Virtual Router Redundancy Protocol is defined in RFC 5798. It provides a solution to the problem by combining two or more physical devices into a logical grouping called a virtual router (VR). The physical devices then operate together to provide a single logical gateway for hosts on the LAN.

A virtual router is configured as the host’s gateway and comprises a number of physical routers. The hosts can only see the virtual router so the number of physical routers that make up the virtual router is transparent. If physical routers in the virtual router fail, then traffic to and from the hosts will still be forwarded, so long as there is at least one functioning physical router, no configuration changes will be required by the hosts.

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