Brocade FastIron Ethernet Switch Platform and Layer 2 Switching Configuration Guide - Manual (Page 96)

VSRP failover
Each Backup listens for Hello messages from the Master. The Hello messages indicate that the
Master is still available. If the Backups stop receiving Hello messages from the Master, the election
process occurs again and the Backup with the highest priority becomes the new Master.
Each Backup waits for a specific period of time, the Dead Interval, to receive a new Hello message
from the Master. If the Backup does not receive a Hello message from the Master by the time the
Dead Interval expires, the Backup sends a Hello message of its own, which includes the Backup's
VSRP priority, to advertise the Backup's intent to become the Master. If there are multiple Backups for
the VRID, each Backup sends a Hello message.
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 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 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 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 the following figure.
VSRP failover
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