Brocade Virtual ADX Global Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 34)

24 Brocade Virtual ADX Global Server Load Balancing Guide
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Proxy for DNS server
1
Typically, you use this set of features when the DNS server contains a single server address for the
actual domain name, but a separate set of proxy server addresses for an alias for that domain
name. When you enable DNS cache proxy and configure the alias for the domain on the GSLB
Brocade Virtual ADX, the GSLB Brocade Virtual ADX:
• Learns the proxy server addresses under the alias on the DNS server instead of the address for
the domain’s actual site. This requires configuration of the alias on the GSLB Brocade Virtual
ADX.
• Responds to client queries for the actual domain name with the best site address from among
the proxy server addresses learned from the DNS server under the alias. This requires that
enable the DNS cache proxy feature.
NOTE
Use this feature only in conjunction with the DNS cache proxy feature. Otherwise, it is possible for
the IP address(es) the Brocade Virtual ADX learns under the real domain name and the addresses
it learns under the alias to be different. When this is the case, the Brocade Virtual ADX does not
make any alterations to the DNS response but instead sends the response back to the client
unaltered. As a result, the Brocade Virtual ADX sends the client the DNS reply with the real domain
name’s server address, instead of one of the proxy addresses configured on the DNS server under
the domain’s alias.
NOTE
The user should remove the DNS domain name from the Brocade Virtual ADX first before deleting it
from the backend DNS server. If the user first removes the domain name from the DNS server
instead, then the DNS server will not have any IP addresses for that domain name and will respond
to the Brocade Virtual ADX backend query for that non-existent domain name with zero IP addresses.
This response is a return code other than NO ERROR (0) which is treated by the Brocade Virtual ADX
as a parsing error. As a result, the Brocade Virtual ADX will not process the response during that time
that the domain name is removed from the backend DNS server and was not removed from the
Brocade Virtual ADX which will then not clean out the IP addresses associated with the DNS domain
name. To ensure that the domain IP addresses for a domain name are cleaned out correctly when
a domain name is removed, the user should first remove the domain name configuration from the
Brocade Virtual ADX followed by the deletion of the domain name on the backend DNS server.
To configure an alias for a domain name, enter the alias after entering the zone name and host
application names, as in the following.
Virtual ADX(config)#gslb dns zone brocade.com
Virtual ADX(config-gslb-dns-brocade.com)#host www http
Virtual ADX(config-gslb-dns-brocade.com)#host www alias www.gslb.brocade.com
The commands configure a zone called “brocade.com”, associate an HTTP host named “www” with
the zone, then associate the alias “www.gslb.brocade.com” with the host and zone.
Syntax: host-info host-name alias alias-name
NOTE
Make sure you configure the alias only after configuring the zone and the host application the alias
is for, as shown in the example above. In addition, make sure you specify the fully-qualified name for
the alias (for example, “www.example1.brocade.com” instead of “www.example1”.