[dns-operations] IPv6 PTR best practice

John Levine johnl at taugh.com
Wed May 9 02:56:31 UTC 2018

In article <5f36f5ccf57842dda020d3f657e24d8a at cira.ca> you write:
>I'm assisting a group to write a best practice document and we're wondering what is the best
>practice on IPv6 PTR for subscribers and for enterprise?
>- What are ISP doing in regards to responding to IPv6 PTR requests?
>- Is not responding to PTR acceptable? When?
>- What applications are requiring IPv6 PTR support?

This has come up at M3AAWG a few times.  The consensus seems to be
that hosts with static addresses should have rDNS to match the forward
DNS but there is no reason to try to paper the whole rDNS with
meaningless PTR records.  The main application that is likely to look
for rDNS is SMTP since mail sent by hosts without matching non-generic
forward and reverse rDNS is about 99.99999% botnet spam.  (Remember
that mail submission is not SMTP, different service on a different

By not responding I hope you mean responding with NXDOMAIN, rather
than no response at all.  That's fine for random hosts not offering

Mark is certainly correct that with some amount of effort it would be
possible for those random v6 hosts to install PTR records but it
doesn't impress me as effort well spent.


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