Brocade Virtual ADX Global Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 41)

Brocade Virtual ADX Global Server Load Balancing Guide 31
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Configuring GSLB protocol parameters
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Virtual ADX(config)#gslb policy
Virtual ADX(config-gslb-policy)#dns check-interval 50
Syntax: [no] dns check-interval num
The num parameter specifies the interval and can be from 1 to 1000000000 seconds. The default
is 30 seconds.
Changing the TTL for DNS records
By default, the Brocade Virtual ADX sets the TTL to 10 seconds in the DNS records in all the replies
from the DNS server for which the Brocade Virtual ADX is performing GSLB. The TTL controls how
long other DNS servers, including the client’s DNS server, keep the query results in their
databases. You can change this TTL.
NOTE
If you configure a host-level policy and apply this policy to a host under a GSLB zone, the Brocade
Virtual ADX uses the host-level policy TTL value to modify the DNS TTL values instead of the DNS TTL
configuration in the global GSLB policy. For more information on configuring the DNS TTL for a
host-level policy, refer to
“Changing the TTL for DNS records” on page 86.
NOTE
We recommend that you do not change the TTL to 0, because this can be interpreted as an error by
some older DNS servers.
The GSLB Brocade Virtual ADX changes the TTL of each DNS record contained in the DNS replies
from the DNS server for which the Brocade Virtual ADX is a proxy. By default, the GSLB Brocade
Virtual ADX changes the TTL to 10. You can modify this to a value from 0 – 1000000000 seconds.
To change the TTL, enter commands such as the following.
Virtual ADX(config)#gslb policy
Virtual ADX(config-gslb-policy)#dns ttl 45
Syntax: [no] dns ttl num
The num parameter specifies the TTL and can be from 0 – 1000000000 seconds. The default is
10 seconds.
For all GSLB features except DNS cache proxy, the command dns ttl configures the Brocade Virtual
ADX to use the TTL from the DNS server. If you are using DNS cache proxy, this command resets the
TTL to 10.
Disabling TTL modification
If you prefer to manage the TTL values solely on the DNS server and do not want the Brocade
Virtual ADX to modify the TTL, you can disable TTL modification. To do so, enter the following
command.
Virtual ADX(config-gslb-policy)#no dns ttl
Syntax: [no] dns ttl
Enabling DNS override
By default, the GSLB Brocade Virtual ADX selects the best site IP address from among the
addresses contained in the DNS reply. You can override the DNS reply for an individual domain
(zone plus a host) by specifying a list of IP addresses, then enabling DNS override. The GSLB
controller replies with all available IP addresses for the respective domain with best IP address on
top of the list.