Brocade Communications Systems 12.4.00 manual Available session capacity metric

2 Advanced GSLB configuration for IPv6

If GSLB default location is not specified and if the requesting client prefix is from an unknown geography, then the GSLB controller assigns "north-america" as its geography. However, if the default location is specified, the GSLB controller assigns the configured geography to unknown client prefixes.

NOTE

This command requires a reload to take effect; therefore, always issue the write memory command after configuring the command.

Enabling default geographic location

The use-default-locationcommand 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 ServerIron ADX is full.

By default, the GSLB ServerIron ADX ignores the default location of new client requests if its client prefix cache if full. Whenever the GSLB ServerIron 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-locationcommand is configured for either the global GSLB policy or the host-level GSLB policy, the ServerIron 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:

ServerIronADX(config)# gslb policy

ServerIronADX(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 217.

To view geographic policy metric settings see “Displaying information about a geographic prefix” on page 235 and “Displaying DNS zone and hosts” on page 237.

Available session capacity metric

If multiple sites are equal after the above comparisons, the GSLB ServerIron ADX prefers the site ServerIron ADX (remote ServerIron ADX) whose session table has the most unused entries.

When comparing sites based on the session table utilization, the GSLB ServerIron 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 ServerIron ADX 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 ServerIron ADX (with 1 million sessions available) is preferred over the second ServerIron ADX because the difference (200,000) is greater than 10% of 1 million. If a third ServerIron ADX has 950,000 sessions available, that ServerIron ADX is equally preferable with the first ServerIron ADX (with 1 million sessions available), because the difference in percentage between the available sessions on the two ServerIron ADXs is only 5%, which is less than the tolerance threshold.

You can change the following parameters associated with the session-table metrics:

218	ServerIron ADX Global Server Load Balancing Guide
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