Allied Telesis AT-S63 - Manual (Page 405)

AT-S63 Management Software Features Guide
Section VII: Routing 405
Overview
This chapter describes the Virtual Router Redundancy Protocol (VRRP) of
the AT-9400 Basic Layer 3 Switches.
One of the functions that switches provide to the hosts of a LAN is to act
as gateways. The local hosts use the gateways to communicate with the
hosts on the WAN. The local hosts are assigned static routes that define
which gateway switch to use as the next hop to reach the WAN. However,
if a statically configured first hop switch fails, the hosts on the LAN will not
be able to communicate with the WAN. If there are a large number of
hosts, it can be time consuming and cumbersome if you have to
reconfigure the static routes on all of the affected hosts.
The Virtual Router Redundancy Protocol provides a solution to the
problem. It combines two or more physical switches into a logical grouping
called a virtual router (VR). The physical switches in the virtual router
operate together to provide a single logical gateway for hosts on the LAN
so that if one gateway fails, the hosts will still be able to communicate with
the WAN.