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Foundry Configuration Guide for the FESX, FSX, and FWSX
8 - 20
© Foundry Networks, Inc.
December 2005
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.
•
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 8.8
Summary of Contents for FastIron Edge Switch X424
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