Forum Discussion

Kelly's avatar
Kelly
Icon for Nimbostratus rankNimbostratus
Sep 07, 2018

multiple DNS::answers from a Datagroup

multiple DNS answers in an iRule

 

We're looking to implement transparent caching on our LTM/DNS F5s. We have a few DNS entries that we want to statically rewrite on the F5. I've written a sample iRule, so that if the DNS::question matches a Datagroup, the response comes from the Datagroup. That works just fine. But we have one particular answer that we want to return multiple answers for a single question, but I can't seem to make it work.

 

Here is a simplified version of the iRule for example:

 

when DNS_REQUEST {
  if { [class match [DNS::question name] equals dns-static-list ] and [DNS::question type] equals "A"}{
  DNS::answer insert  "[DNS::question name]. 10 [DNS::question class] [DNS::question type] [lindex [class match value [DNS::question name] equals dns-static-list] 0]"


  DNS::return 
}                           
}

Obviously the Datagroups won't let you have multiple values tied to the same string, so that doesn't work. I've also tried separating values with a ":", but doesn't return a valid response. I suspect my irule needs much more sophistication to return multiple values, but I didn't see any code examples that I could use as a template.

 

application delivery
BIG-IP DNS
LTM
  • Stanislas_Piro2's avatar
    Stanislas_Piro2
    Icon for Cumulonimbus rankCumulonimbus
    Sep 07, 2018

    In the data group, use space as field separator.

    use this irule:

    when DNS_REQUEST {
    if { [DNS::question type] equals "A" && [class match [DNS::question name] equals dns-static-list ]}{
        foreach val [class match -value [DNS::question name] equals dns-static-list] {
            DNS::answer insert  "[DNS::question name]. 10 [DNS::question class] [DNS::question type] $val"
        }
    DNS::return 
    }                           
}

    Note : Edited to solve class match format with dash missing