Hello messages, Master and owner backup routers, Track ports and track priority – Brocade FastIron Ethernet Switch Layer 3 Routing Configuration Guide User Manual
Page 590
Hello messages
Virtual routers use Hello messages for negotiation to determine the Master router. Virtual routers send
Hello messages to IP Multicast address 224.0.0.18. The frequency with which the Master sends Hello
messages is the Hello interval. Only the Master sends Hello messages. However, a Backup router
uses the Hello interval you configure for the Backup router if it becomes the Master.
The Backup routers wait for a period of time called the dead interval for a Hello message from the
Master. If a Backup router does not receive a Hello message by the time the dead interval expires, the
Backup router assumes that the Master router is dead and negotiates with the other Backup routers to
select a new Master router. The Backup router with the highest priority becomes the new Master.
Master and Owner backup routers
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 priority is changed to
the track priority. In this case, the Owner does not have a higher priority than the Backup router that is
acting as the Master router and the Owner therefore does not resume its position as the Master router.
By default, if a Backup is acting as the Master, and the original Master is still unavailable, another
Backup can "preempt" the Backup that is acting as the Master. This can occur if the new Backup
router has a higher priority than the Backup router that is acting as the Master. You can disable this
behavior. When you disable preemption, a Backup router that has a higher priority than the router that
is currently acting as the Master does not preempt the new Master by initiating a new Master
negotiation.
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 Brocade 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
on page 586, interface e1/6 on Switch 1 owns the IP address to which Host1 directs
route traffic on its default gateway. The exit path for this traffic is through the Switch 1 e2/4 interface.
Suppose interface e2/4 goes down. Even if interface e1/6 is still up, Host1 is cut off from other
networks. In conventional VRRP, Switch 1 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 the Switch 1 VRRP priority to the value of the track priority. In the configuration shown in
on page 586, the Switch 1 priority changes from 255 to 20. One of the parameters
contained in the Hello messages the Master router sends to its Backup routers is the Master router
priority. If the track port feature results in a change in the Master router priority, the Backup routers
quickly become aware of the change and initiate a negotiation to become the Master router.
on page 586, the track priority results in the Switch 1 VRRP priority becoming lower
than the Switch 2 VRRP priority. As a result, when Switch 2 learns that it now has a higher priority
than Switch 1, Switch 2 initiates negotiation to become the Master router and becomes the new
Master router, thus providing an open path for the Host1 traffic. To take advantage of the track port
Hello messages
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FastIron Ethernet Switch Layer 3 Routing Configuration Guide
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