Brocade Virtual ADX Global Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 98)

88 Brocade Virtual ADX Global Server Load Balancing Guide
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Host-level policies for site selection
1
• TCP tolerance
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 modify the application (Layer 7) tolerance, TCP (Layer 4) tolerance, or both, enter commands
such as the following.
GSLB-Virtual ADX(config)#gslb-host-policy abc
GSLB-Virtual ADX(config-gslb-host-policy-abc)#flashback application tolerance 30
GSLB-Virtual ADX(config-gslb-host-policy-abc)#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.
Enabling the Geographic metric
The geographic metric indicates the geographic location of a site. This metric is enabled by default,
which means the GSLB Brocade Virtual ADX uses this metric when evaluating the sites in a DNS
reply to choose the best site.
To enable the Geographic metric for a host-level GSLB policy, enter commands such as the
following.
GSLB-Virtual ADX(config)#gslb-host-policy abc
GSLB-Virtual ADX(config-gslb-host-policy-abc)#geographic
Syntax: [no] geographic
Use the [no] form of the command to disable the Geographic metric.
Enabling the Health Check metric
To enable the Health Check metric for the host-level GSLB policy, enter commands such as the
following.
GSLB-Virtual ADX(config)#gslb-host-policy abc
GSLB-Virtual ADX(config-gslb-host-policy-abc)#health-check
Syntax: [no] health-check
Use the [no] form of the command to disable the Health Check metric.