Virtual Router Redundancy Protocol
(VRRP)
Virtual Router Redundancy Protocol (VRRP) is similar to HSRP, but it is an
open standard (RFC 2338). Two or more devices act as a virtual router. With
VRRP, however, the IP address used can be either a virtual one or the actual
IP address of the primary router.
The VRRP Master router forwards traffic. The master is chosen because 1) it
owns the real address, or 2) it has the highest priority (default is 100). If a
real address is being supported, the owner of real address must be master. A
Backup router takes over if the master fails, and there can be multiple backup
routers. They monitor periodic hellos multicast by the master to 224.0.0.18,
using UDP port 112, to detect a failure of the master router.
Multiple VRRP groups are allowed, just as with HSRP.
Routers in the same VRRP group must belong to the same subnet/VLAN. To
enable VRRP, give this command vrrp group-number ip virtual-IP-address
under the interface connecting to that subnet or VLAN:
Router(config-if)#vrrp 39 ip 10.0.0.1
Control the master and backup elections by configuring priority values from
1.255. If a master VRRP router is shutdown, it advertises a priority of 0.
This triggers the backup routers to hold an election without waiting for the
master�fs hellos to time out.
Router(config-if)#vrrp 39 priority 175
VRRP uses the following timers:
�¡ Advertisement, or hello, interval in seconds. Default is 1 second.
�¡ Master down interval. Equals (3 x advertisement interval) plus skew
time. Similar to a hold or dead timer.
�¡ Skew time. (256.priority) / 256. This is meant to ensure that the
highest priority backup router becomes master, since higher priority
routers have shorter master down intervals.
To change the timers on the master, use the following command because it is
the router that advertises the hellos:
Router(config-if)#vrrp 39 timers advertise 5
To change the timers on the backup routers, use the following command
because they hear the hellos from the master:
Router(config-if)#vrrp 39 timers learn