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John_Heyer_1508's avatar
John_Heyer_1508
Icon for Cirrostratus rankCirrostratus
Jul 21, 2015

Using LTM as secondary caching DNS server with GTM-DNS license

We have a small remote data center with a few dozen servers and a BigIP pair running version 11.6.0.

 

The servers need to use internal DNS in order to function, and are configured to use our internal DNS servers at our main data center. This works great 99.9% of the time, but once in a while the site-to-site VPN connecting the two data centers will become unreliable and DNS queries will time out. The hostnames frequently change IP addesses, so using hosts entries isn't a viable option.

 

I noticed the BigIPs had a 'GTM-DNS' license, so it seems I could use them as secondary or caching DNS servers. This would be a great option, because I can assume the LTMs will always be available. I was able to add the nameservers and zones, but now the question is how do I get the servers to actually use it? With a full GTM license I would create a listener, but that's not an option with the GTM-DNS license.

 

 

application delivery
availability
design
devops
LTM
performance

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  • PeteWhite's avatar
    PeteWhite
    Icon for Employee rankEmployee
    Jul 22, 2015

    You need to create a DNS listener to pickup the DNS traffic - go to Delivery>Listener and add one. Create a DNS profile with caching enabled ( and a cache profile ). You could also consider DNS Express which is a good way of loading specific zones into the F5 device for resolution.

     

  • John_Heyer_1508's avatar
    John_Heyer_1508
    Icon for Cirrostratus rankCirrostratus
    Aug 08, 2015

    Finally found what I was looking for - Fast DNS. The trick is creating a DNS Profile, then applying that to the VS.

     

    1. Create the DNS express zones under DNS -> Zones
    2. Create a DNS cache under DNS -> Caches. Enter the upstream servers as root hints, or create a forward zone called "."
    3. Create a DNS profile in Local Traffic -> Profiles -> Services -> DNS. Set DNS Cache enabled and select the cache name that was created in the previous step
    4. Create a Virtual Server, selected Advanced, and set DNS Profile to the name created in the previous step

    Configuring Fast DNS