Dell PowerConnect B-FCXs, Руководство по настройке

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PowerConnect B-Series FCX Configuration Guide 1105
53-1002266-01
Overview
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Hello messages
VRRP routers use Hello messages for negotiation to determine the Master router. VRRP 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 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 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 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 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, refer to
“Track ports and track priority” on page 1105.
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.
Refer to
“Backup preempt” on page 1119.
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 Dell 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 151 on page 1103, 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 Router1
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, 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 Switch 1 VRRP priority to the value of the track priority. In the configuration
shown in
Figure 151 on page 1103, Switch 1 priority changes from 255 to 20. One of the
parameters contained in the Hello messages the Master router sends to its Backups 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 for Master router.