Least response selection metric, Round robin selection metric, Least response selection – Brocade Communications Systems ServerIron ADX 12.4.00 User Manual
Page 233: Metric, Round robin selection, Configuring administrative preference for a site
ServerIron ADX Global Server Load Balancing Guide
221
53-1002437-01
Advanced GSLB configuration for IPv6
2
•
You can bias a GSLB ServerIron ADX that is also configured as a site ServerIron ADX (for locally
configured VIPs) to always favor itself as the best site. In this case, assign an administrative
preference of 255 to the site for the GSLB ServerIron ADX itself, and assign a lower
administrative distance to the other site ServerIron ADXs, or use the default (128) for those
sites.
NOTE
The administrative preference metric is disabled by default and must be enabled before it is used
in the GSLB policy algorithm. Once enabled, it is placed after the available session capacity metric.
Refer to
“Disabling or re-enabling individual GSLB policy metrics”
Configuring administrative preference for a site
Once enabled, the default administrative preference for sites is 128. You can change the
preference on an individual site basis.
Typically, you can set the administrative preference for a site ServerIron ADX when you define a site.
For example, to set the administrative preference for a site ServerIron ADX to 255, enter a
command such as the following:
ServerIronADX(config)# gslb site us
ServerIronADX(config-gslb-site-us)# si-name slb-1 2001:db8::56 255
To change the preference for a site ServerIron ADX you have already configured, use the same
command syntax. You do not need to reconfigure other site parameters when you change the
preference. For example, to change the preference for a site ServerIron ADX from the default (128)
to 200, enter a command such as the following:
ServerIronADX(config)# gslb site us
ServerIronADX(config-gslb-site-us)# si-name slb-2 2001:db8::56 255 200
Least response selection metric
If multiple sites still compare equally based on all the metrics above, the GSLB ServerIron ADX
selects the site that it has selected least often before. For example, if the GSLB ServerIron ADX has
selected Site 1 and placed its IP address on top in 40% of the DNS replies, but has selected Site 2
60% of the time, then in this instance the GSLB ServerIron ADX selects Site 1. To display the
response selection percentages for the sites you have configured, use the show gslb dns zone
command. Refer to
“Displaying DNS zone and hosts”
This metric is a tie-breaker in case multiple addresses pass through all the above comparisons
without one address emerging as the best choice. If this occurs, the address of the site that has
been selected least often in previous DNS responses is selected.
Least response selection is enabled by default. You can disable the metric only by enabling the
round robin selection metric to act as the tie breaker instead. See the following section.
Round robin selection metric
The round robin selection metric is an alternative to the least response selection metric as the final
tie breaker. When you enable round robin selection, the GSLB ServerIron ADX automatically
disables the least response selection metric, and instead uses the round robin algorithm to select
a site. Round Robin selection chooses the first IP address in the DNS response for the first client
request, then selects the next address for the next client request, and so on.