214 ServerIron ADX Global Server Load Balancing Guide
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Advanced GSLB configuration for IPv6
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The default value for the threshold is 90%. Thus a site ServerIron ADX is eligible to be the best site
only if its session utilization is below 90%. Refer to “Displaying DNS zone and hosts” on page 237
for commands to display a site’s utilization and the capacity threshold.
Active bindings metric
You can configure the ServerIron ADX to prefer an IP address with the highest number of active
bindings.
Active bindings are a measure of the number of active real servers bound to a virtual IP address
(VIP) residing on a GSLB site. The GSLB ServerIron ADX uses the active bindings metric to select
the best IP address for the client. The VIP with the highest number of active bindings is the IP
address preferred by the active bindings metric.
NOTE
By default, the active bindings metric is disabled. Once enabled, it is placed after the available
sessi on ca paci ty me tri c in t he GS LB al gor ithm . You c an ch ange the metr ic or der o r ena ble or di sabl e
other metrics, although we do not recommend this.

DNS response processing

When the active bindings metric is enabled, the GSLB ServerIron ADX evaluates each IP address in
the DNS reply from the server, and selects the IP address with the highest number of active
bindings. The client subsequently makes an SLB request to that IP address.
Active bindings are calculated as follows:
•If the IP address is a VIP residing on a remote site that supports active bindings, then the
number of active bindings equals the number of active real servers bound for application
ports.
•If the IP address is a VIP residing on a remote site that is running older versions of the GSLB
agent software, and consequently does not support the active bindings metric, then the
number of active bindings for the IP address is 1 or 0, depending on the health of the VIP.
•If the IP address is a real server, then the number of active bindings for the IP address is 1 or 0,
depending on the health of the real server.
If all IPs or VIPs have zero active bindings, or if all IPs or VIPs have the same number of active
bindings, the GSLB ServerIron ADX passes them on to the next step in the GSLB algorithm, where
the process of selecting the best IP address continues. Likewise, if two or more IP addresses have
the highest maximum value of active bindings, the GSLB ServerIron ADX passes them on to the
next step in the GSLB algorithm.

Enabling active bindings

Active bindings are a measure of the number of active real servers bound to a virtual IP address
(VIP) residing on a GSLB site. The GSLB ServerIron ADX uses the active bindings metric to select
the best IP address for the client. The VIP with the highest number of active bindings is the IP
address preferred by the active bindings metric.
To configure the active bindings metric, enter the following command:
ServerIronADX(config-gslb-policy)# active-bindings
Syntax: [no] active-bindings