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devious_381979's avatar
devious_381979
Icon for Nimbostratus rankNimbostratus
7 years ago

GTM and SRV Records

Hello

 

We have been asked by our customer to provide DNS resolution based on geography, e.g. US clients get given a US server IP, European clients a European server IP etc. Topology records are clearly a good fit here in terms of technology. There is one thing, however, which I'm a little stumped by, simply because I've never worked with them. They are SRV records.

 

From what I've have read about SRV records & what I know about the GTM it looks like we cannot use Topology records in the same way as standard A records.

 

I know this question might at first sound a little vague but would appreciate a steer on this one from the community. What things I need to consider? Can this even work? Any other questions to ask them to try get to a resolution everyone can be happy with.

 

Thank you.

 

2 Replies

  • devious_381979's avatar
    devious_381979
    Icon for Nimbostratus rankNimbostratus
    7 years ago

    Don’t mean to bump this up but also wondered - is it possible an SRV record could have a target/resource that is itself a Wide IP and therefore we could utilise Topology load balancing?

     

    For example:

     

    _sip._tcp.wideipname

     

  • Kai_Wilke's avatar
    Kai_Wilke
    Icon for MVP rankMVP
    7 years ago

    Hi Devious,

    a SRV records is basically an extended CNAME record with additonal a Weigth/Priority/Port values for the resolved HOST-Name(s).

    when DNS_REQUEST { 

     Searching for DNS request for SRV = _sip._tcp.domain.de

    if { ( [string tolower [DNS::question name]] equals "_sip._tcp.domain.de"  ) 
     and ( [DNS::question type] equals "SRV" ) } then {

             Defining DNS answer for the requested SRV record (Question Name = _sip._tcp.domain.de., ttl = 600, class = IN, type = SRV, priority = 100, weight = 100, port = 5060, hostname = sip.domain.de ) 

            DNS::answer insert "_sip._tcp.domain.de. 600 IN SRV 10 100 5060 sip1.domain.de"
            DNS::answer insert "_sip._tcp.domain.de. 600 IN SRV 20 100 5060 sip2.domain.de"

             Changing "Authorative Answer" DNS header to true.

            DNS::header aa 1 

             Sending the DNS response

            DNS::return

        }
    }
}

    After your DNS client gets the SRV response, it will perform an additional A or AAAA query for the just received HOST names. The subsequent A or AAAA request may then target a wide-IP as usuall...

    Note: The SRV response may already include the A or AAAA DNS responses for the just resolved HOST names to speed up DNS resolution. To make those additional A or AAAA DNS answers GLBS aware you would need a handcrafted logic to perform the country checks and flip the IP based on those information. Its not rocket science, but still far more complicated than using two independent DNS queries/responses...:-)

    Cheers, Kai