Forum Discussion

ashk's avatar
Icon for Cirrus rankCirrus
Aug 08, 2023

GTM DNS ReverseLookup


Hello everyone!!

I was curious as to how the GTM gslb functions when executing a reverse lookup. I have a gslb url that fetches two ltm vips when I perform a nslookup, but when I try to perform a reverse lookup on the IP received, nothing like a failed result appears.

Is this the gslb via GTM default behavior? or something not configured as is?


3 Replies

  • Hey  ashk - I see nobody has answered this yet. I'll pin this to the top of the forum over the weekend to give your question better visibility. 

  • Forward and reverse looks have nothing to do with each other.   If luck the F5 GUI might add a record, but it does not mean things will work.  Have a look under

    forward lookup:  DNS> zone>zonerunner>resource records: view = external (unless you use split DNS),  names = FQDN domain, type=a/aaaa , names = host name/Wide IP names.      you should see "0" TTL records if the Wide IP is defined. 

    forward lookup  DNS> zone>zonerunner>>resource records: view = external (unless you use split DNS),  names =   you see PTR type records if things are defined.   RDATA = FQDN. 

    dig/nslookup   FQDN F5-ip to test forward   - i.e. nslookup 

    dig/nslookup  q=ptr (IP address in reverse).in-addr-arpa.  F5-ip to test reverse 

    i.e. nslookup -q=ptr    (might have the incorrect syntax here)

    For forward lookup the domain above you need to define you as a subdomain using NX records.    Same for reverse but is probably your IPS or who you got the IP address from is the DNS holder.  I think you need a BGP AS number for this setup.   i.e F5 the owner of  *  would need to define NX record for “162” then then in thay zone can the PRT recodes be defined.

    I assume you talking about public DNS and not a private DNS.      

  • seems like DNS "A" records missing for the 2 VS IP addresses in local DNS. please add and test

    if not please share output