Configuring VRRP
Advertisement Messages
VRRP routers use Advertisement messages for negotiation to determine the Master router. VRRP routers send
Advertisement messages to IP Multicast address 224.0.0.18. The frequency with which the Master sends
Advertisement messages is the Hello Interval. Only the Master sends Advertisement messages. However, a
Backup uses the Hello interval you configure for the Backup if it becomes the Master.
The Backup routers wait for a period of time called the Dead Interval for an Advertisement message from the
Master. If a Backup router does not receive an Advertisement message by the time the dead interval expires, the
Backup router assumes that the Master router is dead and negotiates with the other Backups to select a new
Master router. The Backup router with the highest priority becomes the new Master.
If the owner becomes unavailable, but then comes back online, the owner again becomes the Master router. The
owner becomes the Master router again because it has the highest priority. The owner always becomes the
Master again when the owner comes back online.
NOTE: If you configure a track port on the owner and the track port is down, the owner's priority is changed to
the track priority. In this case, the owner does not have a higher priority than the Backup that is acting as Master
and the owner therefore does not resume its position as Master. For more information about track ports, see
"Track Ports and Track Priority", below.
By default, if a Backup is acting as the Master, and the Master is still unavailable, another Backup can "preempt"
the Backup that is acting as the Master. This can occur if the new Backup has a higher priority than the Backup
who is acting as Master. You can disable this behavior if you want. When you disable preemption, a Backup
router that has a higher priority than the router who is currently acting as Master does not preempt the new Master
by initiating a new Master negotiation. See "Backup Preempt" on page 18.
NOTE: Regardless of the setting for the preempt parameter, the owner always becomes the Master again when
it comes back online.
Track Ports and Track Priority
The HP implementation of VRRP enhances the protocol by giving a VRRP router the capability to monitor the
state of the interfaces on the other end of the route path through the router. For example, in Figure 2, interface
e1/6 on Router1 owns the IP address to which Host1 directs route traffic on its default gateway. The exit path for
this traffic is through Router1's e2/4 interface.
Suppose interface e2/4 goes down. Even if interface e1/6 is still up, Host1 is nonetheless cut off from other
networks. In conventional VRRP, Router1 would continue to be the Master router despite the unavailability of the
exit interface for the path the router is supporting. However, if you configure interface e1/6 to track the state of
interface e2/4, if e2/4 goes down, interface e1/6 responds by changing Router1's VRRP priority to the value of the
track priority. In this example, Router1's priority changes from 255 to 20. One of the parameters contained in the
Advertisement messages the Master router sends to its Backups is the Master router's priority. If the track port
feature results in a change in the Master router's priority, the Backup routers quickly become aware of the change
and initiate a negotiation for Master router.
In this example, the track priority results in Router1's VRRP priority becoming lower than Router2's VRRP priority.
As a result, when Router2 learns that it now has a higher priority than Router1, Router2 initiates negotiation for
Master router and becomes the new Master router, thus providing an open path for Host1's traffic. To take
advantage of the track port feature, make sure the track priorities are always lower than the VRRP priorities. The
default track priority for the router that owns the VRID IP address(es) is 2. The default track priority for Backup
routers is 1. If you change the track port priorities, make sure you assign a higher track priority to the owner of the
IP address(es) than you assign to the track priority on the Backup routers.
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