DNS::return

Description

This iRules command skips all further processing after TCL execution and sends the dns packet in the opposite direction.
In the DNS_REQUEST context, DNS::return signals that no further DNS resolution should occur for this request upon completion of the event. To provide a useful response, resource record and header changes must be made in the iRule. The next event triggered is the DNS_RESPONSE event.
In the DNS_RESPONSE context, DNS::return sends a request back for additional processing. This is typically done after the answer, authority and additional sections have been cleared and the query changed to obtain a different response. Great care must be taken to avoid an infinite loop, which can easily occur if the query is not changed before being returned to the resolver.
In both contexts, the use of DNS::return signals what to do after the event has completed, but does not stop processing the current event.
Note: This command should not be confused with the global command return which immediately exits the current event.

Note: This command functions only in the context of LTM iRules and requires the DNS Profile, which is only enabled as part of GTM or the DNS Services add-on.

Syntax

DNS::return

DNS::return

  • Skips all further processing after TCL execution and sends the dns packet in the opposite direction.

Examples

# Send one or more IP addresses for a response to an A query
# Use on an LTM virtual server with a DNS profile enabled
when DNS_REQUEST {
    # Log query details
    log local0. "\[DNS::question name\]: [DNS::question name],\
        \[DNS::question class\]: [DNS::question class],
        \[DNS::question type\]: [DNS::question type]"

    # Generate an answer with two A records
    DNS::answer insert "[DNS::question name]. 111 [DNS::question class] [DNS::question type] 1.1.1.1"
    DNS::answer insert "[DNS::question name]. 111 [DNS::question class] [DNS::question type] 1.1.1.2"

    # Stop further processing of the query after this iRule and send the answer to the client
    DNS::return
}