ServerIron ADX Global Server Load Balancing Guide 229
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Advanced GSLB configuration for IPv6 2
If user configure s this command, he or she will have to manually rehas h at a later conveni ent time.
This command can be used when user does not want to break the persistence for the existing IP
addresses due to a change in weight configuration. User will disable rehashing on weight
configuration change to preserve persistence and instead will rehash manually at a later
convenient time, such as during a maintenance window for the GSLB controller.

Hash persist hold down timer

Hash persist hold down time r is provided to handle the boot up case when rehash on sta te change
from down to up or rehash on weight configuration change is disabled. This hold down timer
specifies how long after boot up, the disabling of rehash on state or weight change takes effect.
Any change to the configured hash weight will result in a rehash during the hold-down time (i.e.
even if you have disabled rehash on weight change), it will become effective only after this
hold-down time has elapsed.
After the GSLB ServerIron ADX boots up, it will perform a back-end query for the IP addresses
associated with the domain. Once it obtains these addresses, the ServerIron ADX will determine
their health. Therefore after boot up, the IPs may come up one after another instead of at the same
time. The weights will get associated with the IPs as they come up; this means that even if rehash is
disabled, a rehash must still be performed to handle this scenario.
To specify how long the disabling of rehash on weight change becomes effective after boot up,
enter a command such as the following:
ServerIronADX(config)# gslb policy
ServerIronADX(config-gslb-policy)# hash-persist hold-down 5
Syntax: hash-persist hold-down <time>
Syntax: [no] hash-persist hold-down <time>
•The <time> parameter specifies the number of minutes (1-255) before rehash disable become
effective after boot up.
•The default is five minutes.
NOTE
This command is provided in the existing hash-based persistence. The same command will be used
for the weighted hash-based persistence as well.
Configuring DNS response parameters
Fragmentation is not supported for the GSLB ServerIron ADX for IPv6.
Therefore, you must either configure an active-only policy or best-only policy or ensure that the
number of IP addresses configured in the IP list is small enough to avoid fragmentation

Configuring an active-only policy

By default, the ServerIron ADX does not remove an IP address from a DNS reply even if the address
fails a health check.
You can configure the ServerIron ADX to remove IP addresses from DNS replies when those
addresses fail a health check. The ServerIron ADX removes the addresses that fail the check so
long as the DNS query still contains at least one address that passes the health check.