40 ServerIron ADX Global Server Load Balancing Guide
53-1002437-01
Configuring GSLB protocol parameters
1
Implementing the weighted IP metric
Beginning with router software release 08.1.00R, you can configure the ServerIron ADX to
distribute GSLB traffic among IP addresses in a DNS reply, based on weights assigned to the IP
addresses. The weights determine the percentage of traffic each IP address receives in
comparison with other candidate IP addresses, which may or may not have assigned weights.
NOTE
You cannot use the weighted IP metric if the weighted site metric is enabled.
The GSLB ServerIron ADX uses relative percentages in order to achieve 100% total weight
distribution, as shown in Table 3 and Table 4. In Table 3, the total of the Configured weighted IP
metrics (2nd column) is 100. The last column shows that the GSLB ServerIron ADX distributes the
traffic to the IP addresses exactly as configured. In this example, traffic distribution is
straightforward because the total weight of all three IP addresses equals 100.
Now consider the example in Table 4. In this example, the total of the Configured weighted IP
metrics (2nd 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 distrib ution.
The weighted IP metric is disabled by default. 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 recommended this.
DNS response processing
When the weighted IP metric option is enabled, the GSLB ServerIron ADX assesses each IP address
in the DNS reply and selects the best IP address for a client, based on the weighted IP metrics
configured in the GSLB policy.
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 is used 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
TABLE 3 Example weighted IP metric configuration
IP address Configured weighted IP metric Relative weighted IP metric
1.1.1.80 50 50%
1.1.2.80 30 30%
1.1.3.80 20 20%
Total 100 100%
TABLE 4 Example weighted IP metric configuration
IP address Configured weighted IP metric Relative weighted IP metric
1.1.1.80 15 33% (15/45 x 100)
1.1.2.80 20 44% (20/45*100)
1.1.3.80 10 22% (10/45*100)
Total 45 100%