Nortel Networks WEB OS 212777 - Manual (Page 248)

Web OS 10.0 Application Guide
248 n Chapter 11: High Availability
212777-A, February 2002
VRRP Overview
In a high-availability network topology, no device can create a single point-of-failure for the
network or force a single point-of-failure to any other part of the network. This means that
your network will remain in service despite the failure of any single device. To achieve this
usually requires redundancy for all vital network components.
VRRP enables redundant router configurations within a LAN, providing alternate router paths
for a host to eliminate single points-of-failure within a network. Each participating VRRP-
capable routing device is configured with the same virtual router IP address and ID number.
One of the virtual routers is elected as the master, based on a number of priority criteria, and
assumes control of the shared virtual router IP address. If the master fails, one of the backup
virtual routers will take control of the virtual router IP address and actively process traffic
addressed to it.
Because the router associated with a given alternate path supported by VRRP uses the same IP
address and MAC address as the routers for other paths, the host’s gateway information does
not change, no matter what path is used. A VRRP-based redundancy schema reduces adminis-
trative overhead because hosts need not be configured with multiple default gateways.
VRRP Components
Each physical router running VRRP is known as a VRRP router.
Virtual Interface Router
Two or more VRRP routers can be configured to form a virtual interface router (VIR). (RFC
2338 calls this entity a virtual router.) The term virtual interface router will be used to distin-
guish this type of entity from a virtual server router (VSR), as described in
“Web OS Exten-
sions to VRRP” on page 259 . When the term virtual router is used herein, the concept applies
to both virtual interface routers and virtual server routers. Each VRRP router may participate
in one or more virtual interface routers.
A virtual interface router acts as a default or next hop gateway for hosts on a LAN. Each vir-
tual interface router consists of a user-configured virtual router identifier (VRID) and an IP
address.