Specifications

CHAPTER 6
First Hop Redundancy
The VRRP Master router forwards traffic. The master is chosen because it owns the real address, or it has the highest
priority. (The default is 100.) If a real address is 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 shut
down, it advertises a priority of 0. This triggers the backup routers to hold an election without waiting for the master’s
hellos to time out.
Router(config-if)# vrrp 39 priority 175
VRRP uses the following timers:
n Advertisement, or hello, interval in seconds. Default is 1 second.
n Master down interval. Equals 3 x advertisement interval plus skew time. Similar to a hold or dead timer.
n Skew time. (256–priority) / 256. This is meant to ensure that the highest priority backup router becomes master
because 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
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CCNP SWITCH 642-813 Quick Reference by Denise Donohue