Dell FCX624-E Laptop User Manual


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PowerConnect B-Series FCX Configuration Guide 359
53-1002266-01
Virtual Switch Redundancy Protocol (VSRP)
10
Layer 2 and Layer 3 redundancy
You can configure VSRP to provide redundancy for Layer 2 only or also for 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.
Layer 2 Switches support Layer 2 VSRP only. Layer 3 Switches support Layer 2 and Layer 3
redundancy. You can configure a Layer 3 Switch for either Layer 2 only or Layer 2 and Layer 3. To
configure for Layer 3, specify the IP address you are backing up.
NOTE
If you want to provide Layer 3 redundancy only, disable VSRP and use VRRPE.
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:
Layer 2 Switches – The Layer 2 Switch with the higher management IP address becomes the
Master.
Switches with management IP addresses are preferred over switches without
management IP addresses.
If neither of the switches has a management IP address, then the switch with the higher
MAC address becomes the Master. (VSRP compares the MAC addresses of the ports
configured for the VRID, not the base MAC addresses of the switches.)
Layer 3 Switches – The Layer 3 Switch whose virtual routing interface has a higher IP address
becomes the master.
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.