Brocade BigIron RX Series Configuration Guide - Manual (Page 509)

BigIron RX Series Configuration Guide 431
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Overview of Virtual Switch Redundancy Protocol (VSRP)
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Layer 2 and Layer 3 redundancy
You can configure VSRP to provide redundancy for Layer 2 only or both for Layer 2 and Layer 3:
• Layer 2 only – The Layer 2 links are backed up but specific IP addresses are not backed up.
• Layer 2 and Layer 3 – The Layer 2 links are backed up and a specific IP address is also backed
up. Layer 3 VSRP is the same as VRRPE. However, using VSRP provides redundancy at both
layers at the same time.
Master election and failover
Each VSRP device advertises its VSRP priority in Hello messages. During Master election, the VSRP
device with the highest priority for a given VRID becomes the Master for that VRID. After Master
election, the Master sends Hello messages at regular intervals to inform the Backups that the
Master is healthy.
If there is a tie for highest VSRP priority, the tie is resolved as follows:
• The device whose virtual routing interface has a higher IP address becomes the master.
• If no IP address is configured, the device’s base MAC address is used.
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.
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 76