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Site persistence in GSLB using hashing
SLB-ServerIronADX(config)#gslb policy
SLB-ServerIronADX(config-gslb-policy)#hash-persist persist-rehash-disable
The second command disables the behavior described in the section
a domain or change of state"
Syntax: hash-persist persist-rehash-disable <time-out>
The <time-out> parameter specifies the number of seconds before an IP address is removed from
the hash table when that IP becomes down. The default is 5 seconds.
Consider the example where a user has configured this command and set the following IP
addresses for www.foo.com.
1.1.1.42 (rank 1)
1.1.1.44 (rank 2)
The hash table allocation is as follows.
0
.42
If the user now configures a new IP address 1.1.1.43 for domain www.foo.com and this IP address
is healthy, the controller will still not do any reassignments of the hash buckets to this new IP
address to preserve persistence for all hash buckets.
Hash-persist hold-down: boot up considerations if rehash disabled
If rehash is disabled, then rehash on introduction of new IP address or change of IP address state
from down to healthy is disabled. However, the boot up case must be taken into account.
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. The health of some of the IPs may be determined by health checks done by the GSLB
ServerIron ADX and some by means of distributed health check. Therefore after boot up, the IPs
may come up one after another instead of at the same time. If rehash is disabled, a rehash must
still be performed for this case.
To specify how long the disabling of rehash becomes effective after boot up, enter a command
such as the following:
SLB-ServerIronADX(config)#gslb policy
SLB-ServerIronADX(config-gslb-policy)#hash-persist hold-down 5
Syntax: 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.
Manually forcing rehash for a domain
Consider the case where you disable rehashing on introduction of a new IP address or change of IP
address state from down to healthy, such as described in the previous section.
In such a scenario, you may wish to force a rehash at a feasible time in order to allow the new IP
addresses to also be included in the hash table. For this case, to manually rehash the hash table,
enter a command such as the following:
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ServerIron ADX Global Server Load Balancing Guide
"Rehash: new IP address for
53-1002437-01
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