Brocade Communications Systems ServerIron ADX 12.4.00 - Manual (Page 104)

92 ServerIron ADX Global Server Load Balancing Guide
53-1002437-01
DNS cache proxy
1
In configurations where the ServerIron ADX and DNS server are co-located, the additional round
trip time between the ServerIron ADX and DNS server is usually negligible. However, if the
ServerIron ADX and DNS server are in different networks, the delay can become significant. In this
case, the DNS cache proxy can help enhance performance by eliminating the exchange between
the ServerIron ADX and DNS server for responses to client queries.
The DNS cache proxy feature is disabled by default. When the feature is disabled, the ServerIron
ADX forwards client requests to the actual DNS server, applies the GSLB policy to the responses,
then sends the optimized response to the client. In this case, the round trip time between the
ServerIron ADX and DNS server is part of the overall round trip time between when the client sends
the request and when the client receives the response.
If the GSLB ServerIron ADX cannot respond directly to the client for the requested domain (for
example, because the domain is not configured on the GSLB ServerIron ADX), the ServerIron ADX
sends the request through to the DNS server. This is the same behavior as when the DNS cache
proxy feature is disabled.
NOTE
You can combine the DNS cache proxy feature with the DNS override feature (added in software
release 06.0.03) to completely eliminate the separate DNS server. In this case, the ServerIron ADX
contains all the required DNS information. Refer to
“Combining the DNS cache proxy and DNS
override features” on page 94.
Enabling DNS cache proxy
To enable DNS cache proxy, enter the following commands.
ServerIronADX(config)# gslb policy

ServerIronADX(config-gslb-policy)# dns cache-proxy
Syntax: [no] dns cache-proxy
Displaying DNS cache proxy state
To display the current GSLB policy settings, which include the DNS cache proxy state, enter the
following command at any level of the CLI.
ServerIronADX(config)# show gslb policy

Default metric order: ENABLE

Metric processing order:

1-Server health check

2-Remote ServerIronADX's session capacity threshold

3-Round trip time between remote ServerIronADX and client

4-Geographic location

5-Remote ServerIronADX's available session capacity

6-Server flashback speed

7-Least response selection


DNS active-only: DISABLE DNS best-only: DISABLE DNS override: DISABLE

DNS cache-proxy: ENABLE DNS transparent-intercept: DISABLE

remaining rows omitted for brevity...
Syntax: show gslb policy
The command output shown in bold type in the example indicates the DNS cache proxy state. The
state can be one of the following: