Brocade Communications Systems ServerIron ADX 12.4.00 - Manual (Page 98)

86 ServerIron ADX Global Server Load Balancing Guide
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Affinity
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• If the reply contains a VIP on the ServerIron ADX associated with the prefix that the client’s IP
address is in, the ServerIron ADX places the VIP at the top of the address list in the reply. (This
assumes that the VIP passes the applicable health checks if they are enabled.)
• If the reply contains more than one VIP on the ServerIron ADX associated with the prefix that
contains the client’s IP address, the ServerIron ADX selected the VIP that has been selected
least often. (This is the last metric in the GSLB policy and is used as a tiebreaker).
• If the VIP fails a health check, or if the reply does not contain a VIP on the ServerIron ADX
associated with the prefix that contains the client’s IP address, the ServerIron ADX uses the
other GSLB metrics in the policy to reorder the list.
You can configure up to 50 affinities. The IP prefix in each affinity can have a value from 0-31. You
can associate only one ServerIron ADX with a prefix. However, you can associate multiple prefixes
with the same ServerIron ADX.
If you configure more than one affinity, it is possible for a client’s IP address to be within the
prefixes of more than one affinity definition. In this case, the ServerIron ADX uses the affinity
whose prefix is a more specific match for the client. For example, assume that the GSLB ServerIron
ADX in
Figure 5 contains the following affinities:
• IP prefix: 192.0.0.0/8, site ServerIron ADX: 209.157.22.209 (slb1 in the sunnyvale site)
• IP prefix: 192.108.0.0/16, site ServerIron ADX: 209.157.22.210 (slb2 in the sunnyvale site)
The client IP address 192.108.1.100 falls within both prefixes. However, prefix 192.108.0.0/16 is a
more precise match than prefix 192.0.0.0/8. Therefore, the ServerIron ADX uses the affinity
definition that contains prefix 192.108.0.0/16. If the VIP for the more precise prefix is not available
(for example, if it fails a health check), the ServerIron ADX uses the standard GSLB policy to select
the best site.
You can configure a default affinity definition by using the prefix 0.0.0.0/0 in the definition. When
you configure a default affinity definition, the ServerIron ADX prefers a VIP on the ServerIron ADX
associated with the prefix 0.0.0.0/0 for all clients except those whose addresses are within a prefix
configured in another affinity definition. Configuring a default affinity definition is optional. If you do
not configure one, the ServerIron ADX uses the standard GSLB policy for clients whose addresses
are not within the prefix of an affinity definition.
Defining the affinity
To enter the GSLB affinity configuration level, enter the following command.
ServerIronADX(config)#gslb affinity

ServerIronADX(config-gslb-affinity)#
Syntax: gslb affinity
Once you are there, refer to the ServerIron ADX by its GSLB site name and ServerIron ADX name or
by its management IP address, by entering the following command.
ServerIronADX(config-gslb-affinity)#prefer ?

ASCII string site name

A.B.C.D ServerIronADX management address
Syntax: [no] prefer <site-name> <si-name> | <si-ip-addr> for <ip-addr> <ip-mask> |
<ip-addr>/<prefix-length>
The <site-name> and <si-name> parameters specify the remote site and a ServerIron ADX at that
site. If you use this method, you must specify both parameters.