34 ServerIron ADX Global Server Load Balancing Guide
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Configuring GSLB protocol parameters
1
When you enable DNS override, the GSLB ServerIron ADX replaces the IP addresses in the DNS
reply with the “best” of the proxy server addresses you specify. The GSLB ServerIron ADX
determines which proxy server IP address is the best using the GSLB policy metrics. For information
about the metrics, refer to “GSLB policy” on page 6.
NOTE
DNS override is a global parameter but a list of proxy IP addresses are associated with a specific
host in a specific domain. If there are no proxy addresses for a given host, the GSLB ServerIron ADX
sends the DNS reply unaltered. An exception is if you have enabled the active only feature, in which
case the reply contains only the active addresses. Refer to “Removing IP addresses for sites that fail
a health check” on page 31.
To display the DNS override state, enter the show gslb policy command. The state is shown in the
DNS override field. Refer to “Displaying the default GSLB policy” on page 175 for more information.
To display information about the IP addresses selected for a specific domain and host, enter the
show gslb dns zone command. Refer to “Displaying DNS zone and hosts” on page 170.
Changing the GSLB policy metrics
“GSLB policy” on page 6 describes the default policy the GSLB ServerIron ADX uses to evaluate the
IP addresses in the DNS replies from the DNS server for which the ServerIron ADX is configured as
a proxy. You can change the policy by changing or deleting individual metrics. Table 2 lists the GSLB
policy metrics. The metrics are listed in their default order. The metric described in the first row is
the first metric the GSLB ServerIron ADX uses by default, and so on.
For example, you can change the following:
•Metric processing order: you can change the order in which the metrics are applied.
•Metric state: you can disable or re-enable some metrics.
•Session-table capacity and threshold tolerance: you can modify the values for these metrics.
•FlashBack tolerance: you can modify the value for this metric.
•RTT values: you can individually modify the cache interval, cache prefix, tolerance, and explore
percentage.
•Connection load parameters: you can adjust the number of data collection intervals and the
relative weights give n to the intervals.
NOTE
If the GSLB policy rejects all of the sites, the GSLB ServerIron ADX sends the DNS reply unchanged
to the client.