1 Global Server Load Balancing overview
NOTE
You cannot use the weighted IP metric if the weighted site metric is enabled.
The GSLB ServerIron ADX uses relative percentages in order to achieve 100% total weight distribution.
To configure weighted IP metrics, refer to “Implementing the weighted IP metric” on page 40.
Weighted site metric
You can configure the ServerIron ADX to distribute SLB traffic among GSLB sites based on weights configured for the sites. The weights determine the percentage of traffic each site will receive in comparison with other sites, which may or may not have weights.
NOTE
You cannot use the weighted site metric if the weighted IP metric is enabled.
You assign weights to GSLB sites. Each GSLB site may consist of one or more ServerIron ADXs, but the weight is applicable to the site as a whole.
The GSLB ServerIron ADX uses relative percentages in order to achieve 100% total weight distribution.
Site ServerIron ADX’s session capacity threshold
The GSLB protocol supplies statistics for the session tables on each site ServerIron ADX. The session table contains an entry for each open TCP or UDP session on the site ServerIron ADX. Each ServerIron ADX has a maximum number of sessions that it can hold in its session table. Through the GSLB protocol, the GSLB ServerIron ADX learns from each remote ServerIron ADX the maximum number of sessions and the number of available sessions on that ServerIron ADX.
The capacity threshold specifies how close to the maximum session capacity the site ServerIron ADX (remote ServerIron ADX) can be and still be eligible as the best site for the client. This mechanism provides a way to shift load away from a site before the site becomes congested.
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 GSLB information” on page 165 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.
To configure active bindings metrics, refer to “Enabling the active bindings metric” on page 118.
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