220 ServerIron ADX Global Server Load Balancing Guide
53-1002437-01
Advanced GSLB configuration for IPv6
2
You can modify the following FlashBack parameters:
•Application tolerance
•TCP toleran ce
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.