For more information regarding the security incident at F5, the actions we are taking to address it, and our ongoing efforts to protect our customers, click here.

Forum Discussion

yuanqiang_22112's avatar
yuanqiang_22112
Icon for Nimbostratus rankNimbostratus
Jun 07, 2016

DNS Forward(cname)

Hello everyone GTM (11.5.1 hotfx10) create a Forward profile with zonerunner for host,the day I found host unresolved is wrong ,I reboot BIG-IP,and host unresolved is right. why is this ? If there is dns cache in F5? DO you know the command for clearing GTM dns cache ?

 

application delivery
BIG-IP DNS

1 Reply

  • IanB's avatar
    IanB
    Icon for Employee rankEmployee
    Jun 08, 2016

    DNS Cache is the fourth option in the expanded menu in your screenshot (right below 'Zones'). Have you created a dns cache ? If not, there won't be one by default, and the default DNS profile disables caching anyway.

    The first thing to work out is what handled the query on the BigIP DNS (GTM). It could be GSLB, caching, zonerunner, dns express, or bind (named). Any of those could have returned a result.

    If 100.66.7.253 is a DNS listener (DNS / Delivery / Listeners), then check the statistics for that listener, then under Profiles, select the DNS profile ('dns' by default), to see what process handed the request

    If the box hasn't done anything else, then you'll see non-zero numbers against one of those processes. Update us when you find what it was

    Given that you've configured a forwarder, you're probably expecting bind (named) to handle the request. Bind will remember the answer for as long as the TTL in the response says it can do so. You can clear this by restarting bind:

    bigstart restart named