ServerIron ADX Global Server Load Balancing Guide 39
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Configuring GSLB protocol parameters 1
ServerIronADX(config)# gslb policy
ServerIronADX(config-gslb-policy)# health-check
ServerIronADX(config-gslb-policy)# geographic
To enable the administrative preference metric, which is disabled by default, enter the following
commands.
ServerIronADX(config)# gslb policy
ServerIronADX(config-gslb-policy)# preference
To specify the site connection limit and enable the connection limit metric, enter commands such
as the following:
ServerIronADX(config)# gslb policy
ServerIronADX(config-gslb-policy)# connection-load limit 500
This command sets the site connection limit to 500 connections. During site comparison, the GSLB
policy discards sites that have an average load of new connections that is higher than the amount
you specify. All other sites are passed to the next GSLB policy metric as potential candidates.
Clearing DNS selection counters
The GSLB ServerIron ADX maintains DNS selection statistics for each IP address based on DNS
requests served for a particular domain name. These DNS selection statistics include:
•How many times the IP address was selected as the best IP address
•Which metrics were used for making the IP address selection
•The percentage of times an IP address was selected in comparison with other IP addresses in
the same domain name
Use the show gslb dns zone command to display the DNS selection statistics.
DNS selection statistics are used to implement GSLB metrics such as least response, weighted site
and weighted IP metrics. Each of these metrics base subsequent selections on the number of
times the IP address was previously selected. For example, the weighted site metric selects the IP
address that has the least relative weight, the calculation of which is based on the selection
counter of that IP address.
It can be advantageous to use the Clear DNS Selection Counters feature in conjunction with GSLB
metrics. Consider the following examples:
•The Least Response metric selects the IP address that has been selected the least number of
times when compared to other IP addresses. If an IP address has become available after
having been down for some time, it might suddenly become flooded with subsequent traffic
because its selection counter is low. Clearing the counters for that zone can prevent a flood to
this IP address.
•You can also use this feature to test the GSLB implementation before deploying it on a wider
scale. You can analyze the effectiveness of each GSLB metric by rearranging the metric order
and using the Clear Counters feature to start over without having to reload the software.
To clear DNS selection counters globally or per zone, without reloading the software, or to clear out
any DNS requests for any client, enter a command such as the following:
ServerIronADX# clear gslb dns zone zone1
Syntax: clear gslb dns zone-name [<name>]
Replace <zone-name> with the zone for which you want to clear the DNS selection counters. To
clear the counters globally (for all zones), do not enter a <zone-name>.