We are a small ISP, using linux DNS servers. Recently a client has asked us to create a rDNS zone for a specific IP address, which is used for a mail server. They keep getting message failures for some emails due to lack of PTR records and valid rDNS.

We created the rDNS zone the same way as all of the other rDNS zones are created. The only difference is that, outside of our network the PTR record is not found, but only for that specific IP address.

Does anyone know what could be the cause of this?

  • Are you a LIR, or do you get your IPs from an upstream LIR? – NickW Apr 2 '14 at 12:29
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    Has the rDNS zone in question been delegated to your company? – joeqwerty Apr 2 '14 at 14:25

Use the trace option in dig to debug delegation path from the root nameservers. A couple of re-runs is usually needed to follow different referals.

For example ip-address of serverfault.com:

dig +trace -x
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  • I did the trace option and it got my primary ns server as an answer. – user3271583 Apr 2 '14 at 12:35
  • And your primary DNS server did or did not respond with the correct PTR record? – HBruijn Apr 2 '14 at 13:06
  • I think it did not respond with the correct PTR record. Not sure what to do next. – user3271583 Apr 2 '14 at 13:22
  • To test if your DNS is set up correctly test with dig -x <customer_ip> @<your_primary_dns> ; if that doesn't return the equivalent of 3063 IN PTR stackoverflow.com. your name server setup is incorrect. Maybe a missing trailing dot if it's bind? (or an extra dot)? – HBruijn Apr 2 '14 at 13:52
  • It returned the correct equivalent... – user3271583 Apr 2 '14 at 14:16

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