Brocade Virtual ADX Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 118)

102 Brocade Virtual ADX Server Load Balancing Guide
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Policy-based SLB
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Deleting existing PBSLB sessions
By default, when a PBSLB server group configuration changes, the client sessions with that group
remain open. For example, if a client has sessions associated with Group A, but Group A’s
configuration changes and moves the client sessions to Group B, the sessions with Group A are still
open. You can change this behavior by enabling the scan-session-table-after-config-change feature.
With this feature enabled, old connections are deleted and a new connection is set up with a new
group whenever a PBSLB server's configuration changes.
To enable this feature, enter the following command.
Virtual ADX(config)#server pbslb scan-session-table-after-config-change
Syntax: [no] server pbslb scan-session-table-after-config-change
Use the no form of the command to disable this feature. The feature is disabled by default.
PBSLB pool failsafe group
The PBSLB pool failsafe group feature allows a Brocade Virtual ADX to direct traffic away from a
given server pool to a "default pool" in situations where the servers in the server pool become
unavailable.
Overview of PBSLB pool failsafe group
When PBSLB is used to filter traffic based on source IP address, a Brocade Virtual ADX looks up a
group id for the client to forward the incoming request to. If all the servers in the group fail, the
Brocade Virtual ADX sends a TCP reset to the client, causing the request to fail. This feature allows
you to configure a failsafe group, which will be used to forward traffic, in case the group designated
for a client source-ip address fails. The following section outlines the behavior of this feature in two
scenarios.
For IP addresses present in the PBSLB list:
• If the group-id is 0 (deny group), the traffic is denied (RST in case of TCP and drop in case of
udp).
• If the group-id is not 0, if the servers are healthy, traffic is load balanced among servers as per
predictor.
• If all servers of the group are in a failed state, traffic is load balanced among "failsafe" group
servers.
• If all of the servers of the "failsafe" group are in a failed state, traffic is denied (RST in case of
TCP and drop in case of UDP).
For IP addresses not present in the PBSLB list:
• If the default-group-id is not configured or is configured as 0 (deny group), traffic is denied.
• If the default-group-id is configured, traffic is load balanced among default-group servers as
per predictor.
• If all of the servers of the default-group are in a failed state, the traffic is load balanced among
"failsafe" group servers.
• If all of the servers of the failsafe group are in a failed state, the traffic is denied.