Brocade Virtual ADX Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 331)

Brocade Virtual ADX Server Load Balancing Guide 315
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Configuring additional HA parameters
6
Configuring a backup group ID
Hot Standby HA redundancy enables a Brocade Virtual ADX to serve as an automatic backup for
another Brocade Virtual ADX. Each Hot Standby HA pair consists of two Brocade Virtual ADX
devices. You can configure up to 127 Hot Standby HA pairs within a single L2 broadcast domain. To
enable this support, configure a backup group ID on each of the Brocade Virtual ADX devices. Both
Brocade Virtual ADX devices in a given pair have the same ID. The ID uniquely identifies the pair.
When you configure a backup group ID, both Brocade Virtual ADX devices in a Hot Standby HA pair
use the ID when exchanging backup information. If a Brocade Virtual ADX receives a backup
information packet, but the packet’s backup group ID does not match the Brocade Virtual ADX’s
backup group ID, the Brocade Virtual ADX discards the packet.
If the broadcast domain contains multiple Hot Standby HA pairs, you must configure backup group
IDs on all pairs. If the broadcast domain contains only one Hot Standby HA pair, you do not need to
configure a backup group ID.
To configure a backup group ID, enter the following command.
Virtual ADX(config)#server backup-group 1
Syntax: [no] server backup-group id
The id variable specifies the backup group ID. Enter a number from 1 to 7. The default value is 0.
Enter the same ID on both Brocade Virtual ADX devices in a Hot Standby HA pair. Do not enter the
same ID on a Brocade Virtual ADX that is not one of the Brocade Virtual ADX devices in the Hot
Standby HA pair. This feature is turned on by default.
Use the show server backup command in a Hot Standby HA topology to display the backup ID
information. If there is a group-ID mismatch, both Brocade Virtual ADX devices become active
(instead of one standby and one active).
Setting the backup timer
The standby Brocade Virtual ADX assumes the active role if the it does not receive a Hello message
or Layer 4 session synchronization data from the active Brocade Virtual ADX within a certain
number of seconds since having received the last Hello message or synchronization data.
By default, the standby Brocade Virtual ADX waits one second since having received the last Hello
message or data to receive a new message or data. If the standby Brocade Virtual ADX does not
receive a new Hello message or data within one second, the standby Brocade Virtual ADX assumes
that the active Brocade Virtual ADX is no longer available and takes over the active role.
In some configurations, particularly those in which the active Brocade Virtual ADX is performing a
lot of processing, it is possible for frequent failovers to occur. In this situation, although the active
Brocade Virtual ADX is still available and actively serving load balancing or other requests, the
active Brocade Virtual ADX does not always send the Hello message or synchronization data in time
for the standby Brocade Virtual ADX. As a result, the standby Brocade Virtual ADX takes over the
active role. If similar conditions cause the newly active Brocade Virtual ADX to sometimes miss
sending the Hello messages or synchronization data in time, failover occurs again.
You can prevent unnecessary state flapping between the two Brocade Virtual ADXs by increasing
the backup timer. When you increase the backup timer, the standby Brocade Virtual ADX waits
longer to receive new Hello messages or synchronization data from the active Brocade Virtual ADX.
As a result, flapping is reduced or eliminated.