96 ServerIron ADX Global Server Load Balancing Guide
53-1002437-01
Transparent DNS query intercept
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•Redirect the client queries to a proxy DNS server and send the reply unchanged. The
ServerIron ADX redirects the client request to the alternate DNS server and sends the
response, as is, to the client. The alternate DNS server could be a ServerIron ADX configured
for GSLB, in which case the reply has the best address(es) for the client.
•Directly respond to client queries using the IP addresses configured for the domain. The
ServerIron ADX does not forward or redirect the query to the actual or proxy DNS servers.
Instead, it directly responds to the client by applying GSLB policy to pick the best IP address
from among the IP list configured for the domain.
NOTE
A ServerIron ADX configured for transparent intercept redirects or directly responds to client
requests only for domain configured on the ServerIron ADX. If the domain name requested by the
client is not configured on the ServerIron ADX, it forwards the query to the actual DNS server without
intercepting, and the reply is untouched by GSLB.
Example
Figure 6 shows an example of a configuration that uses transparent DNS query intercept. In this
example, the ServerIron ADX is configured to intercept all client queries to the zone brocade.com
and redirect them to the proxy DNS server and apply GSLB on the reply. The ServerIron ADX uses its
configured source-ip to make sure the DNS reply from the proxy server comes to it.
•The client’s local DNS server sends a recursive query for brocade.com to the authoritative DNS
server (209.157.23.130).
•The ServerIron ADX intercepts and redirects client query to proxy DNS server
(209.200.22.100).
•The proxy DNS server sends response back to the ServerIron ADX��s source IP address
(209.157.23.100).
•The ServerIron ADX changes the source address in the reply to the authoritative DNS server’s
address and the destination address from the ServerIron ADX’s source-IP to the client’s IP
address.
•The client receives the DNS response with the authoritative DNS server’s source IP address.
The ServerIron ADX’s interception and redirection is transparent to the client.
FIGURE 6 Transparent DNS query intercept configuration