| Configuring GSLB protocol parameters | 1 | |
TABLE 5 | Example weighted site metric configuration |
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GSLB site | Configured weighted site metric | Relative weighted site metric |
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San Jose | 50 | 50% |
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New York | 30 | 30% |
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London | 20 | 20% |
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Total | 100 | 100% |
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Now consider the example in Table 6. 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.
TABLE 6 | Example weighted site metric configuration |
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IP address | Configured weighted site metric | Relative weighted site metric |
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San Jose | 15 | 33% (15/45 * 100) |
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New York | 20 | 44% (20/45 * 100) |
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London | 10 | 22% (10/45 * 100) |
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Total | 45 | 100% |
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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 “Changing the order of GSLB policy metrics” on page 37.
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.
ServerIron ADX Global Server Load Balancing Guide | 43 |
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