Brocade Communications Systems 12.4.00 manual Administrative preference metric

2 Advanced GSLB configuration for IPv6

You can modify the following FlashBack parameters:

•Application tolerance

•TCP tolerance

The GSLB ServerIron ADX uses a tolerance value when comparing the FlashBack speeds of different sites. The tolerance value specifies the percentage by which the FlashBack speeds of the two sites must differ in order for the ServerIron ADX to choose one over the other. The default FlashBack tolerance is 10%. Thus, if the FlashBack speeds of two sites are within 10% of one another, the ServerIron ADX considers the sites to be equal. However, if the speeds differ by more than 10%, the ServerIron ADX prefers the site with the lower FlashBack speed.

FlashBack speeds are measured at Layer 4 for all TCP/UDP ports. For the application ports known to the ServerIron ADX, the FlashBack speed of the application is also measured.

When the ServerIron ADX compares the FlashBack speeds, it compares the Layer 7 (application-level) FlashBack speeds first, if applicable. If the application has a Layer 7 health check and if the FlashBack speeds are not equal, the ServerIron ADX is through comparing the FlashBack speeds. However, if only the Layer 4 health check applies to the application, or if further tie-breaking is needed, the ServerIron ADX then compares the Layer 4 FlashBack speeds.

To change the tolerances for the response times of TCP and application health checks, when used as a metric for selecting a site, enter commands such as the following:

ServerIronADX(config)# gslb policy

ServerIronADX(config-gslb-policy)# flashback application tolerance 30

ServerIronADX(config-gslb-policy)# flashback tcp tolerance 50

Syntax: [no] flashback application tcp tolerance <num>

The application tcp parameter specifies whether you are modifying the tolerance for the Layer 4 TCP health check or the Layer 7 application health checks. You can change one or both and the values do not need to be the same. For each, you can specify from 0-100. The default for each is 10.

Administrative preference metric

The administrative preference is an optional metric. This metric is a numeric preference value from 0-255 that you assign to each site ServerIron ADX, to select that ServerIron ADX if the previous metrics do not result in selection of a best site. The GSLB policy prefers the site ServerIron ADX with the highest administrative preference value.

The administrative preference allows you to do the following:

•You can temporarily change the preference of a site to accommodate changing network conditions. For example, if sites are offering proxy content service, the link between a site proxy server farm and the content origin may be highly congested, making that site less desirable. This factor is not visible to the ServerIron ADXs and thus cannot be reflected in the other GSLB metrics.

•You can temporarily disqualify a site ServerIron ADX from being selected, without otherwise changing the site’s configuration or the GSLB ServerIron ADX’s configuration. For example, you can perform maintenance on the site ServerIron ADX without making network changes. In this case, set the administrative preference to 0.

220	ServerIron ADX Global Server Load Balancing Guide
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