Brocade Virtual ADX Global Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 164)

154 Brocade Virtual ADX Global Server Load Balancing Guide
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Advanced GSLB configuration for IPv6
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Enabling default geographic location
The use-default-location command enables you to ensure that the geographic policy metric is used
to load balance client requests even if the client prefix cache maintained by the GSLB Brocade
Virtual ADX is full.
By default, the GSLB Brocade Virtual ADX ignores the default location of new client requests if its
client prefix cache if full. Whenever the GSLB Brocade Virtual ADX cannot create a new entry in the
client prefix cache because it has already exceeded the limit, it ignores the geographic policy
metric and falls to the next metric in the GSLB policy.
If the use-default-location command is configured for either the global GSLB policy or the host-level
GSLB policy, the Brocade Virtual ADX uses the default location of the client and the geographic
policy metric when determining how to distribute the client’s request.
To ensure that the geographic policy metric is used, enter commands such as the following:
Virtual ADX(config)#gslb policy
Virtual ADX(config-gslb-policy)#use-default-location
The default location of the client corresponds to the default location configured on the GSLB
controller. If no default location is configured on the GSLB controller, then n-america is assigned by
default. For more information, see
“Specifying GSLB controller locations” on page 153.
To view geographic policy metric settings see “Displaying information about a geographic prefix” on
page 167 and “Displaying DNS zone and hosts” on page 169.
Available session capacity metric
If multiple sites are equal after the above comparisons, the GSLB Brocade Virtual ADX prefers the
site ADX device (remote ADX device) whose session table has the most unused entries.
When comparing sites based on the session table utilization, the GSLB Brocade Virtual ADX
considers the sites to be equal if the difference in session table utilization does not exceed the
tolerance percentage. The tolerance percentage ensures that minor differences in utilization do not
cause frequent, and unnecessary, changes in site preference.
For example, suppose one ADX device has 1 million sessions available, and another has 800,000
sessions available. Also assume that the tolerance is 10% (the default). In this case the first ADX
device (with 1 million sessions available) is preferred over the second ADX device because the
difference (200,000) is greater than 10% of 1 million. If a third ADX device has 950,000 sessions
available, that ADX device is equally preferable with the first ADX device (with one million sessions
available), because the difference in percentage between the available sessions on the two ADX
devices is only 5%, which is less than the tolerance threshold.
You can change the following parameters associated with the session-table metrics:
• Session 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%.
• Available session capacity tolerance: Specifies the percentage by which the number of
available sessions on the site ADX device can differ from the number of available sessions on
another site ADX device and still be considered an equally good site.
You can change these parameters on an individual basis.