2 | Advanced GSLB configuration for IPv6 |
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| TABLE 20 | 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 server (host) health 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 for IPv6 policy metrics” on page 206.
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.
Traffic distribution specifications
In general, DNS response selection counters are maintained per IP address, per domain name. For example, suppose you configure three GSLB sites with assigned weights. All three sites host the application www.gslb.com and sites New York and London also host ftp.gslb.com, as illustrated below.
www.gslb.com
VIP 2001:DB8::1 belongs to San Jose with a weight of 50
VIP 2001:DB8::2 belongs to New York with a weight of 30
VIP 2001:DB8::3 belongs to London with a weight of 20
212 | ServerIron ADX Global Server Load Balancing Guide |
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