Brocade Virtual ADX Global Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 78)

68 Brocade Virtual ADX Global Server Load Balancing Guide
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DNS cache proxy
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When you enable the DNS override feature, you also need to configure an IP list for the required
domains. The Brocade Virtual ADX performs health checks on the IP addresses configured for the
domains and directly responds to client queries by using the GSLB policy to select the best IP
address from the IP list configured for the requested domain.
By combining the DNS cache proxy feature with the DNS override feature, you can configure the
Brocade Virtual ADX to directly respond to client requests, without ever consulting the authoritative
DNS server.
NOTE
A GSLB Brocade Virtual ADX does not contain all the features of a real DNS server and thus cannot
completely replace the DNS server.
NOTE
Although you do not need a real DNS server when you combine DNS cache proxy with DNS override,
you still need to configure a virtual IP address for the DNS server. Clients send queries to the virtual
IP address.
For information about configuring DNS cache proxy, refer to “DNS cache proxy” on page 65. For
information about configuring DNS override, see “Enabling DNS Override” in the “Configuring
Global Server Load Balancing” chapter.
To add a virtual IP address to which the clients can send their DNS queries, enter a command such
as the following.
Virtual ADX(config)#server virtual-name-or-ip dns-proxy 10.157.23.87
Virtual ADX(config-vs-dns-proxy)#port dns
The command in this example adds IP address 10.157.23.87 as a virtual server. When clients send
their DNS queries to this address, the Brocade Virtual ADX processes the queries.
GSLB DNS type any query
DNS servers perform the translation between fully qualified domain names and IP addresses. DNS
supports a number of record types such as IPv4 Address records (A records), IPv6 Address records
(AAAA records), Name Server records (NS records), Mail Exchange (MX records), Canonical Name
records (CNAME records) and so on.
Brocade GSLB Brocade Virtual ADX performs GSLB on client queries for IPv4 address records (A
records). In GSLB topologies, when the client query comes in for any of the other record types, the
GSLB Brocade Virtual ADX forwards the query to the backend DNS server and sends the DNS
response unaltered to the client.
DNS supports a special query type called "ANY". If the client sends a DNS query with type ANY, the
DNS response contains all the records configured for that domain. For example, if two A records
and two MX records are configured for www.example10.com and the client sends a type ANY query
for www.example10.com, then the DNS response contains all four records: two A records and two
MX records.
GSLB Brocade Virtual ADX is able to handle DNS type ANY queries. If the client sends a DNS query
with type ANY, GSLB Brocade Virtual ADX identifies it as a supported query type and performs GSLB
on the A records contained in the response.