Table 5, Table 6 – Brocade Communications Systems ServerIron ADX 12.4.00 User Manual
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ServerIron ADX Global Server Load Balancing Guide
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Configuring GSLB protocol parameters
1
Now consider the example in
. In this example, the total of the Configured weighted site
metrics (second column) does not equal 100. However, as illustrated in the last column, the GSLB
ServerIron ADX uses relative percentages in order to achieve 100% total weight distribution.
By default, the weighted site metric is disabled. When 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 we do not recommend this. For more information, refer to
DNS response processing
When the weighted site metric is enabled, the GSLB ServerIron ADX selects an IP address
belonging to a particular site to be the best IP address in the DNS reply to a client. The client
subsequently makes an SLB request to that IP address.
Using the weighted site metric, the GSLB algorithm calculates a relative weight for each IP address
and selects the IP address with the least relative weight. The GSLB ServerIron ADX uses the
following criteria to calculate the relative weight of an 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 site metric, and the
weights of sites to which they belong
•
A calculated weight assigned to an IP address, based on the following criteria:
•
If the IP address is a real server, then the calculated weight is zero
•
If the IP address is a Virtual IP (VIP), the weight is calculated based on the site the VIP
belongs to, the weight of the site, and the number of candidate VIPs belonging to the site
and being evaluated by the weighted site metric
If an IP address has a relative weight of zero, or if an IP address belongs to a site that does not have
an assigned weight, the IP address is not selected as the best IP address for a client. Note that all
real servers have a relative weight of zero, as do VIPs that belong to sites with no assigned weights.
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.
TABLE 5
Example weighted site metric configuration
GSLB site
Configured weighted site metric
Relative weighted site metric
San Jose
50
50%
New York
30
30%
London
20
20%
Total
100
100%
TABLE 6
Example weighted site metric configuration
IP address
Configured weighted site metric
Relative weighted site metric
San Jose
15
33% (15/45 * 100)
New York
20
44% (20/45 * 100)
London
10
22% (10/45 * 100)
Total
45
100%