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Leilow214's avatar
Leilow214
Icon for Altostratus rankAltostratus
Aug 09, 2022

F5 DNS iRule for disabling DNS Express for a CNAME query on a particular domain

Hey Folks!

So we're using an F5 DNS as a resolver for some of our linux servers and at the same time it is the authoritative DNS for that particular domain

let's say we host example.com on the F5 DNS.

When we create a CNAME record on example.com

test.example.com CNAME test.aws.com

and test.aws.com hosts 3 A records.

What happens is DNS Express wont let us use the recursion since its built that way.

What we want is to disable DNSExpress when a CNAME query for example.com specifically. 

Is there an irule to do that?

Any help is greatly appreciated!

Thank you!

 

 

 

application delivery

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  • LiefZimmerman's avatar
    LiefZimmerman
    Icon for Admin rankAdmin
    Aug 15, 2022

    Leilow214 - this has been hanging out for a while - have you figured out a path forward?
    If not...let me know if anything has changed since the 9th and I'll see if I can find someone to lend a hand.

    • Leilow214's avatar
      Leilow214
      Icon for Altostratus rankAltostratus
      Aug 15, 2022

      Hey Lief,

      Good day!

      Thanks for checking out on my question, I havent tested any solutions yet. But here's what Irule I did, Im not sure if this would work.

      Name: CNAME_DNSX_iRule

      when DNS_REQUEST {

      if { ([string toupper [DNS::question type]] eq "CNAME") }
      {
      DNS::disable dnsx
      }
      }

       

      Thank you.

      • JRahm's avatar
        JRahm
        Icon for Admin rankAdmin
        Aug 16, 2022

        yes, that should work fine, DNS iRules processing is handled up front (as shown in this lightboard lesson). You can further refine by extending your if condition to the targeted domain in the query received if necessary.

        I'm pretty sure DNS::question type returns all caps already, but you could test to make sure and then eliminate the extra string command for the comparison.