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hc_andy_35682's avatar
hc_andy_35682
Icon for Nimbostratus rankNimbostratus
Feb 15, 2012

F5 GTM - DNS timeouts after several nslookups

Hi All,

 

 

We are using the F5 GTM to be the authoratative dns for our sub-domain abc.xyz.com.

 

 

We've configured zonerunner with the relevant zone details and A records to serve dns requests for this zone.

 

 

My question relates to the fact that if I do a windows nslookup against the listener IP configured on the F5 (10.61.63.52), after about several nslookup (maybe 30+ times) I eventually get a dns timeout error (as seen below).

 

 

Does the F5 have some sort of protection mechanism that automatically blocks the same IP querying it after X amount of times??? I wouldn't think so, but asking anyway :)

 

 

This is significant to us because we have a set of windows dns servers that are set as our primary dns servers on our PC's. The windows DNS servers have a forwarder configured on them to the F5's listener IP to handle any requests for abc.xyz.com.

 

 

Every now and then we will have DNS issues with resolving myhost.abc.xyz.com and the Windows guys are saying that there is nothing wrong with their DNS server and point to the fact that if they do a direct lookup on the F5's listener IP as seen below, it eventually times out - so it's a F5 issue!!

 

 

Is this just a bug with the Windows nslookup too??? Are there any checks/logs on the F5 that we can do to rule out it being an issue with the F5.

 

 

> myhost.abc.xyz.com

 

Server: [10.61.63.52]

 

Address: 10.61.63.52

 

 

Name: myhost.abc.xyz.com

 

Address: 10.61.34.10

 

 

> myhost.abc.xyz.com

 

Server: [10.61.63.52]

 

Address: 10.61.63.52

 

 

Name: myhost.abc.xyz.com

 

Address: 10.61.34.10

 

 

> myhost.abc.xyz.com

 

Server: [10.61.63.52]

 

Address: 10.61.63.52

 

 

DNS request timed out.

 

timeout was 2 seconds.

 

Name: myhost.abc.xyz.com

 

Address: 10.61.34.10

 

 

> myhost.abc.xyz.com

 

Server: [10.61.63.52]

 

Address: 10.61.63.52

 

 

Name: myhost.abc.xyz.com

 

Address: 10.61.34.10

 

 

Thanks.

 

 

Andy

 

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  • Cory_50405's avatar
    Cory_50405
    Icon for Noctilucent rankNoctilucent
    Oct 25, 2012
    My suggestion is to run a tcpdump on the GTM and get a capture of the traffic for analysis. This should give you an idea of what is happening. The possibilities of what could be causing this aren't limited to the F5. Could be network congestion, could be some misconfiguration elsewhere in the network, etc. A packet capture will help.
  • venezuz_133353's avatar
    venezuz_133353
    Icon for Nimbostratus rankNimbostratus
    Sep 10, 2013

    I have the same issue. I use 2 listener (2 ISP) to have a HA on my FQDN. When i do a nslookup on a FQDN using this LoadBalancing method (listeners) I have a timeout of 2 sec and after the fqdn is resolved with the IP. When i publish a FQDN directly pointing on the Virtual Server public IP I don't have the timeout and the FQDN is directly resolved.

     

    My listeners are configured with UDP protocol. My Wide IP has a TTL of 30 I set a custom profile of protocol UDP with an iddle timeout of 5 seconds and Datagram LB check.

     

    I deduce that the problem is on the configuration of the HA mecanism of DNS on the BigIP. I don't know how can I resolve this issue...

     

  • boneyard's avatar
    boneyard
    Icon for MVP rankMVP
    Sep 10, 2013

    if you are sure it is the BIG-IP then just raise a ticket with TAC and let them show you are wrong or fix it.