Brocade Virtual ADX Global Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 166)

156 Brocade Virtual ADX Global Server Load Balancing Guide
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Advanced GSLB configuration for IPv6
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The GSLB Brocade Virtual 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 Brocade Virtual 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 Brocade Virtual ADX considers the sites to be equal. However, if the speeds differ by
more than 10%, the Brocade Virtual 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 Brocade Virtual ADX, the FlashBack speed of the application is also measured.
When the Brocade Virtual 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 Brocade Virtual 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 Brocade Virtual 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:
Virtual ADX(config)#gslb policy
Virtual ADX(config-gslb-policy)#flashback application tolerance 30
Virtual ADX(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 ADX device, to select that ADX device if the previous metrics do
not result in selection of a best site. The GSLB policy prefers the site ADX device 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 ADX devices and thus cannot be reflected in the other GSLB
metrics.
• You can temporarily disqualify a site ADX device from being selected, without otherwise
changing the site’s configuration or the GSLB Brocade Virtual ADX’s configuration. For
example, you can perform maintenance on the site ADX device without making network
changes. In this case, set the administrative preference to 0.
• You can bias a GSLB Brocade Virtual ADX that is also configured as a site ADX device (for
locally configured VIPs) to always favor itself as the best site. In this case, assign an
administrative preference of 255 to the site for the GSLB Brocade Virtual ADX itself, and assign
a lower administrative distance to the other site ADX devices, or use the default (128) for those
sites.