122 ServerIron ADX Global Server Load Balancing Guide
53-1002437-01
Host-level policies for site selection
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GSLB-ServerIronADX(config)# gslb-host-policy abc
GSLB-ServerIronADX(config-gslb-host-policy-abc)# metric-order set health-check
round-trip-time capacity num-session flashback
Syntax: [no] metric-order set <list>
The <list> parameter is a list of the metrics you want to use, in the order you want the GSLB
ServerIron ADX to use them for the host-level policy. The GSLB ServerIron ADX uses the metrics in
the order you specify. You can specify one or more of the following:
•active bindings: The ServerIron ADX’s preference for the IP address with the highest number of
active bindings
•capacity: The remote ServerIron ADX’s session capacity threshold.
•connection-load: The site ServerIron ADX’s average number of new connections per second
•flashback: The site ServerIron ADX’s Flashback speed (how quickly the GSLB receives the
health check results)
•geographic: The geographic location of the server
•health-check: The Layer 4 and application health checks
•num-session: The remote ServerIron ADX’s available session capacity
•preference: The administratively configured preference for the site ServerIron ADX
•round-trip-time: The round-trip time between the remote ServerIron ADX and the DNS client
•weighted ip: The administratively configured traffic distribution method for the ServerIron ADX
based on weights for IP addresses
•weighted site: The administratively configured traffic distribution method for the ServerIron
ADX based on weights for GSLB Sites
There are no parameters for the least response selection or round robin selection metrics. These
metrics are tie-breakers. Only one of them is enabled at a time and the one that is enabled will
always be the last metric in the host-level policy.
NOTE
We recommend that you always use the health check as the first metric. Otherwise, it is possible
that the GSLB policy will not select a "best” choice, and thus send the DNS reply unchanged. For
example, if the first metric is geographic location, and the DNS reply contains two sites, one in North
America and the other in South America, for clients in South America the GSLB policy favors the
South American site after the first comparison. However, if that si te is down , the GSLB policy will find
that none of the sites in the reply is the “best” one, and thus send the reply unchanged.
You cannot disable or change the position of the least response selection metric. The GSLB
ServerIron ADX uses this metric as a tie-breaker if the other comparisons do not result is selection
of a “best” site.
Resetting the order of the metrics
To reset the order of the GSLB policy metrics in a host-level policy to the default order, and
re-enable all disabled metrics, enter commands such as the following:
GSLB-ServerIronADX(config)# gslb-host-policy abc
GSLB-ServerIronADX(config-gslb-host-policy-abc)# metric-order default
Syntax: metric-order default