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F5_324021
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Sep 24, 2017
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GTM Design For External DNS Queries

Hello,

 

I'm a little bit confused here as I'm setting up my upcoming project design which includes 2 boxes with GTM and LTM modules each, and each box will be located in a site (SITE A, SITEB),GTM will be handling the external DNS queries for a specific domain name (),

 

First is it possible configure a private IP on the GTM and NAT it with a public IP on our firewall,

 

So the DNS flow for my design is as the following:-

 

Internet Client --->External DNS (ISP DNS)-->Firewall--->GTM--->LTM--->VS

 

What should be done from the external DNS side, should the ISP just delegate the DNS queries matching the to the public IP configured on our firewall which will traverse all the DNS queries to our GTM,

 

Waiting for your recommendations

 

Thanks Smiley Happy

 

  • Hello,

     

    what about the A record ip address of the Ns gtm1 is it the ip address of the listener configured on the GTM or is it the self ip address of the GTM?

     

    Also i have another question when doing the same delegation from the external DNS (Internet side) the delegation configuration will be as you stated the following:-

     

    ns1.gtm.example.com A X.X.X.X wip.example.com NS ns1.gtm.example.com

     

    Here the X.X.X.X Ip address will be the piblic ip address of the GTM to be natted on the firewall or what?regardless if its the listener or the self ip of the GTM.

     

    Hope you can help me

     

    Thank you..

     

19 Replies

  • Kevin_K_51432's avatar
    Kevin_K_51432
    Historic F5 Account

    Greetings,

    The flow looks like this:
    Internet
    |
    Firewall
    | |
    | |<------>GTM
    |
    |<------>LTM
    

    The GTM server object's Address is the Firewall IP address (basic TCP connectivity), while the Translation IP address is the internal LTM IP address (this address is learned via iquery).

    K14707: Configuring BIG-IP DNS server objects for BIG-IP devices that reside behind a firewall NAT

    https://support.f5.com/csp/article/K14707

    Kevin

  • Hello,

     

    what about the A record ip address of the Ns gtm1 is it the ip address of the listener configured on the GTM or is it the self ip address of the GTM?

     

    Also i have another question when doing the same delegation from the external DNS (Internet side) the delegation configuration will be as you stated the following:-

     

    ns1.gtm.example.com A X.X.X.X wip.example.com NS ns1.gtm.example.com

     

    Here the X.X.X.X Ip address will be the piblic ip address of the GTM to be natted on the firewall or what?regardless if its the listener or the self ip of the GTM.

     

    Hope you can help me

     

    Thank you..

     

    • Kevin_K_51432's avatar
      Kevin_K_51432
      Historic F5 Account

      Greetings,

       

      "what about the A record ip address of the Ns gtm1 is it the ip address of the listener configured on the GTM or is it the self ip address of the GTM?"

       

      This would be the listener address (or the IP address that receives and processes DNS queries).

       

      "Here the X.X.X.X Ip address will be the piblic ip address of the GTM to be natted on the firewall or what?"

       

      Yes, this would be the external IP address that the firewall offers to the world.

       

      Hope this is helpful!

       

      Kevin

       

    • F5_324021's avatar
      F5_324021
      Icon for Cirrus rankCirrus

      Hello Kevin,

       

      Thats great,

       

      So once the DNS request reaches the GTM and pick the VS that should hold the traffic request is the GTM going to reply with the public ip of the VS?if yes, and how it will know the public address if its configured as a private address on the LTM?

       

      Thanks again.

       

    • Kevin_K_51432's avatar
      Kevin_K_51432
      Historic F5 Account

      Greetings,

      I hope terrible ascii topology is helpful:

          Internet
      
          Firewall <------+
          |          11.22.33.44
          |               |
          LTM             |
          192.168.10.44   |
                         GTM
      

      Using the topology, the server object for LTM would be created as follows:

          gtm server testing {
              addresses {
                  11.22.33.44 {
                      device-name /Common/testing
                      translation 192.168.10.44
                  }
              }
      

      GTM will connect through the firewall to the LTM. It will use the firewall IP (address) for DNS queries, while understanding that the real IP address (translation) is 192.168.10.44.

      The added benefit here is that GTM is going to probe the same path as customer will, so if there's a firewall issue, GTM will detect and act accordingly (depending on configuration).

      Virtual servers would follow the same IP address scheme. One Important, you can't auto-discover unfortunately. From K14707:

      Important: The BIG-IP DNS system does not auto discover virtual severs on the BIG-IP LTM devices that reside behind a firewall NAT. You must manually add the BIG-IP LTM virtual servers to the BIG-IP DNS configuration.

          my_vip_one {
            destination 11.22.33.45:http   
            enabled
            monitor none
            translation-address 192.168.10.45
            translation-port any
      
          }
      

      This article will give all of the necessary background to understand more if you are curious:

      https://support.f5.com/csp/article/K14707

      Thanks!

      Kevin