Overview Of Vrrp - Foundry Networks Switch and Router Installation And Configuration Manual

Foundry Switch and Router Installation and Configuration Guide
Overview
The following sections describe VRRP and VRRPE. The protocols both provide redundant paths for IP
addresses. However, the protocols differ in a few important ways. For clarity, each protocol is described
separately.

Overview of VRRP

VRRP is a protocol that provides redundancy to routers within a LAN. VRRP allows you to provide alternate router
paths for a host without changing the IP address or MAC address by which the host knows its gateway. Consider
the situation shown in Figure 21.1.
Router1
Figure 21.1 Router1 is Host1's default gateway but is a single point of failure
As shown in this example, Host1 uses 192.53.5.1 on Router1 as the host's default gateway out of the sub-net.
If this interface goes down, Host1 is cut off from the rest of the network. Router1 is thus a single point of failure for
Host1's access to other networks.
If Router1 fails, you could configure Host1 to use Router2. Configuring one host with a different default gateway
might not require too much extra administration. However, consider a more realistic network with dozens or even
hundreds of hosts per sub-net; reconfiguring the default gateways for all the hosts is impractical. It is much
simpler to configure a VRRP virtual router on Router1 and Router2 to provide a redundant path for the host(s).
21 - 2
Internet
or
enterprise Intranet
e 2/4
e 1/6 192.53.5.1
Internet
or
enterprise Intranet
e 3/2
Router2
e 1/5
Host1
Default Gateway
192.53.5.1
December 2000