Brocade Multi-Service IronWare Switching Configuration Guide (Supporting R05.6.00) - Manual (Page 586)

556 Multi-Service IronWare Switching Configuration Guide
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Layer 2 redundancy
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When a Backup sends a Hello message announcing its intent to become the Master, the Backup
also starts a hold-down timer. During the hold-down time, the Backup listens for a Hello message
with a higher priority than its own:
• If the Backup receives a Hello message with a higher priority than its own, the Backup resets
its Dead Interval and returns to normal Backup status.
• If the Backup does not receive a Hello message with a higher priority than its own by the time
the hold-down timer expires, the Backup becomes the new Master and starts forwarding Layer
2 traffic on all ports.
If you increase the timer scale value, each timer’s value is divided by the scale value. To achieve
sub-second failover times, you can change the scale to a value up to 10. This shortens all the VSRP
timers to 10 percent of their configured values.
VSRP priority calculation
Each VSRP device has a VSRP priority for each VRID and its VLAN. The VRID is used during Master
election for the VRID. By default, a device’s VSRP priority is the value configured on the device
(which is 100 by default). However, to ensure that a Backup with a high number of up ports for a
given VRID is elected, the device reduces the priority if a port in the VRID’s VLAN goes down. For
example, if two Backups each have a configured priority of 100, and have three ports in VRID 1 in
VLAN 10, each Backup begins with an equal priority, 100. This is shown in
Figure 159 .
FIGURE 159 VSRP priority
However, if one of the VRID’s ports goes down on one of the Backups, that Backup’s priority is
reduced. If the Master’s priority is reduced enough to make the priority lower than a Backup’s
priority, the VRID fails over to the Backup.
Figure 160 shows an example.
FIGURE 160 VSRP priority recalculation