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HAPTER
VRRP
This chapter shows you how to configure and monitor the Virtual Router Redundancy Protocol
(VRRP) on the Switch.
44.1 VRRP Overview
Each host on a network is configured to send packets to a statically configured default gateway
(this Switch). The default gateway can become a single point of failure. Virtual Router Redundancy
Protocol (VRRP), defined in RFC 2338, allows you to create redundant backup gateways to ensure
that the default gateway of a host is always available.
In VRRP, a virtual router (VR) represents a number of physical layer-3 devices. An IP address is
associated with the virtual router. A layer-3 device having the same IP address is the preferred
master router while the other Layer-3 devices are the backup routers. The master router forwards
traffic for the virtual router. When the master router becomes unavailable, a backup router assumes
the role of the master router until the master router comes back up and takes over.
The following figure shows a VRRP network example with the switches (A and B) implementing one
virtual router VR1 to ensure the link between the host X and the uplink gateway G. Host X is
configured to use VR1 (192.168.1.20) as the default gateway. If switch A has a higher priority, it is
the master router. Switch B, having a lower priority, is the backup router.
Figure 319 VRRP: Example 1
172.16.1.1
172.16.1.100
172.16.1.10
If switch A (the master router) is unavailable, switch B takes over. Traffic is then processed by
switch B.
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