CANOGA PERKINS 9175 Configuration Guide - Manual (Page 125)

CanogaOS Configuration Guide
20-2
20.4 VRRP Process
Typically, end hosts are connected to the enterprise network through a single router (first
hop router) that is in the same Local Area Network (LAN) segment. The most popular
method of configuration is for the end hosts to statically configure this router as their
default gateway. This minimizes configuration and processing overhead. The main
problem with this configuration method is that it produces a single point of failure if this
first hop router fails.
Figure 20-1: VRRP Process
The Virtual Router Redundancy Protocol attempts to solve this problem by introducing
the concept of a virtual router, composed of two or more VRRP routers on the same
subnet. The concept of a virtual IP address is also introduced, which is the address that
end hosts configure as their default gateway. Only one router (called the master) forward
packets on the behalf of this IP address. In the event that the Master router fails, one of
the other routers (Backup) assumes forwarding responsibility for it.
Figure 20-2: VRRP Protocol
At first glance, the configuration outlined in might not seem very useful, as it doubles the
cost and leaves one router idle at all times. This, however, can be avoided by creating
two virtual routers and splitting the traffic between them.