Brocade Virtual ADX Global Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 18)

8 Brocade Virtual ADX Global Server Load Balancing Guide
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Global Server Load Balancing overview
1
Weighted IP metric
You can configure the Brocade Virtual ADX to distribute GSLB traffic among IP addresses in a DNS
reply, based on weights assigned to the IP addresses. The weights determine the percentage of
traffic each IP address receives in comparison with other candidate IP addresses, which may or
may not have assigned weights.
NOTE
You cannot use the Weighted IP metric if the Weighted Site metric is enabled.
The GSLB Brocade Virtual 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 39.
Weighted Site metric
You can configure the Brocade Virtual 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 ADX devices, but the
weight is applicable to the site as a whole.
The GSLB Brocade Virtual ADX uses relative percentages in order to achieve 100% total weight
distribution.
Site ADX device’s session capacity threshold
The GSLB protocol supplies statistics for the session tables on each site ADX device. The session
table contains an entry for each open TCP or UDP session on the site ADX device. Each Brocade
Virtual ADX has a maximum number of sessions that it can hold in its session table. Through the
Brocade GSLB protocol, the GSLB Brocade Virtual ADX learns from each remote ADX device the
maximum number of sessions and the number of available sessions on that ADX device.
The capacity threshold specifies how close to the maximum session capacity the site ADX device
(remote ADX device) 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 ADX device is eligible to be the best site only
if its session utilization is below 90%. refer to
“Displaying GSLB information” on page 104 for
commands to display a site’s utilization and the capacity threshold.