Brocade Virtual ADX Global Server Load Balancing Guide (Supporting ADX v03.1.00) User Manual
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Brocade Virtual ADX Global Server Load Balancing Guide
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Host-level policies for site selection
1
When you configure a GSLB host-level policy, by default, the DNS TTL modification is enabled in the
policy with a TTL value of 10 seconds. When you apply this policy to a host under a GSLB zone, the
Brocade Virtual ADX uses the policy TTL value to modify the DNS TTL values in the responses to the
client for queries made to the host; irrespective of the DNS TTL configuration in the global GSLB
policy.
You can change the DNS TTL in a host-level policy. For example, to configure a TTL value of
45 seconds under the GSLB host-level policy of www.abc.com, enter the following commands.
GSLB-Virtual ADX(config)#gslb-host-policy abc
GSLB-Virtual ADX(config-gslb-host-policy-abc)#dns ttl 45
Syntax: [no] dns ttl [num]
If you enter the dns ttl command without a TTL value, the TTL is set to 10 seconds.
NOTE
Brocade recommends that you do not change the TTL to 0, because this can be interpreted as an
error by some older DNS servers.
Use the no form of the dns ttl command to disable the Brocade Virtual ADX from modifying the TTL
value in the DNS response with the TTL configured under the policy.
GSLB-Virtual ADX(config-gslb-host-policy-abc)#no dns ttl
Use the show gslb policy host-policy-all or show gslb policy host-policy- name command to display
the host-level DNS TTL information in the following fields:
•
The Modify DNS response TTL field displays whether the modification of DNS TTL is enabled.
•
The DNS TTL field displays the modified TTL value.
“Displaying a host-level policy”
for examples of these show commands and their output.
Disabling or re-enabling the Flashback metric
The Flashback metric indicates how quickly the GSLB Brocade Virtual ADX receives Layer 4-7
health check results. 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 disable this metric, enter the following command.
Virtual ADX(config)#gslb-host-policy abc
Virtual ADX(config-gslb-host-policy-abc)#no flashback
To re-enable this metric, enter the following command.
Virtual ADX(config)#gslb-host-policy abc
Virtual ADX(config-gslb-host-policy-abc)#flashback
Syntax: [no] flashback
NOTE
When both the Health Check metric and the Flashback metric are disabled for the host-level GSLB
policy, the GSLB Brocade Virtual ADX will not perform any Layer 4 or Layer 7 health checks for the
hosts/zones to which this policy applies.
Modifying Flashback tolerance
You can modify the following Flashback parameters:
•
Application tolerance