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Dwimmerlaik_254's avatar
Dwimmerlaik_254
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Nov 30, 2011

iApp f5.dns Question

I have an iApp Application Service created on my Big IP LTM VE appliance to load-balance our internal DNS servers. Everything is working just fine with the exception that if I do a nslookup request from a client configured with the IP address of the Virtual Server as primary DNS, it responds with something like the following:

 

 

Server: UnKnown

 

Address: {Virtual Server IP Address}

 

 

 

I have created a static DNS entry for the Virtual Server and I am able to perform a nslookup of the FQDN and have it resolve to the appropriate Virtual Server IP Address.

 

 

 

Is there a configuration step that I'm missing so that nslookup requests will respond with the Virtual Server name instead of "UnKnown"?

 

automation
devops
iApps
management
TMSH
  • Brent_Blood_768's avatar
    Brent_Blood_768
    Historic F5 Account
    Nov 30, 2011
    I think that iApp sets up a pair of virtual servers - one for UDP and another for TCP - that both load balance DNS queries to a pool comprised of the servers that you entered. With such a setup, BIG-IP shouldn't be doing anything to the replies other than passing them back to the client. Things to look at that come to mind:

     

     

    1. Are the servers in the DNS pool being marked up by their monitors? If the servers are down, is it because of a networking issue like the BIG-IP not having a route to reach those servers, or is the LTM just not happy with the data in the reply?

     

    2. What does tcpdump on the BIG-IP show for the traffic that is sent from the BIG-IP to one of the DNS servers? Is the server responding back with a correct reply?
  • Dwimmerlaik_254's avatar
    Dwimmerlaik_254
    Icon for Nimbostratus rankNimbostratus
    Dec 01, 2011
    You can chalk this one up to my own stupidity. I forgot to add a PTR record for the Big-IP appliance so it wasn't able to do a reverse lookup on the IP address.

     

     

    D'oh!