ServerIron ADX Global Server Load Balancing Guide 209
53-1002437-01
Advanced GSLB configuration for IPv6 2
When you configure a ServerIron ADX for GSLB, it learns a series of IP addresses from its
configured DNS real servers. Then it performs Layer 3, Layer 4, and if possible, Layer 7 health
checks against those IP addresses.
The GSLB ServerIron ADX determines which health checks to use based on the host applications
you specify. For example, if a host name is associated with both HTTP and FTP applications, the
ServerIron ADX sends the site Layer 4 TCP health checks (one for HTTP and one for FTP) and also
sends a separate Layer 7 HTTP health check and a separate Layer 7 FTP health check. The site
must pass all the health checks or it is disqualified from being the best site.
If a host application uses a port number that is not known to the ServerIron ADX and supported by
GSLB, the ServerIron ADX cannot perform a Layer 7 health check on the application but still
performs a Layer 4 TCP or UDP health check on the port. Health check parameters such as retry
interval, number of retries, and so on are global parameters.
Weighted IP metric
GSLB ServerIron ADX supports the weighted IP policy metric for load balancing of IPv6 addresses.
When enabled, the GSLB controller distributes GSLB traffic among IP addresses in the IP list,
based on weights assigned to the IP addresses.
The weight configured for an IP address determines the percentage of traffic that a IP address
receives in comparison with other candidate IP addresses, which may or may not have assigned
weights.
Using the weighted IP metric, the GSLB algorithm calculates a relative weight for each IP address
and selects the IP address with the least relative weight.
The following criteria are used to calculate the relative weight of each IP address:
•The number of times the GSLB ServerIron ADX selected the IP address as the best IP address
to reply to a client
•The number of eligible IP addresses to be evaluated by the weighted IP metric and their
weights
•The weight assigned to the IP address
If an IP address has a relative weight of zero, or if it does not have a weight assigned to it, the IP
address is not selected as the best IP address for a client.
If two or more IP addresses have the same relative weight, or if all of the IP addresses have a
relative weight of zero, all of the IP addresses with the same relative weight are passed on to the
next step in the GSLB algorithm, where the process of selecting the best IP address continues.
NOTE
The weighted IP metric is disabled by default. Once enabled, it is placed second in the GSLB
algorithm, after the health check metric. You can change the metric order and enable or disable
other metrics, although Brocade does not recommended this. “Changing the order of GSLB for IPv6
policy metrics” on page 206.

Enabling the weighted IP metric

To configure weighted IP metrics, you must enable the weighted IP metric and specify the weights
of IP addresses.