[dns-operations] IPv6 PTR best practice

Mark Andrews marka at isc.org
Wed May 9 01:23:55 UTC 2018

> On 9 May 2018, at 3:42 am, Jacques Latour <Jacques.Latour at cira.ca> wrote:
> Hi All,
> 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?

Never.  The DNS is a query/response protocol.  Not responding is not part of the protocol.

> - What applications are requiring IPv6 PTR support?

The same set that require it for IPv4.

> Any feedback appreciated,

ISP’s really haven’t looked at what can work for populating PTR records.

Companies using Active Directory have the end node populate the the PTR
records using GSS-TSIG signed UPDATE requests.  Similar could work for
ISP but every time someone mentions this they huff and puff and say it
won’t work.

They see their kludge of pre-populating the reverse address space as being
“good enough” for IPv4 and just want to do the same for IPv6 rather than
actually look for solutions that will work.

In named today we have the ability to authorise the adding of PTR records
based on the TCP source address. can add a PTR record at by sending the update request over TCP.  Similarly
for IPv6.

With DNSSEC named updates RRSIGs as they fall due.  Removing PTR records
after a interval would be just as simple a process.  A heap structure and
a timer that triggers a removal when the timer expires.  Resending the
UPDATE request resets the timer.

All the client has to do is send a UPDATE request to add a PTR record for
the machines name whenever it renews its IP address (DHCP or via RA).
Active Directory clients do a UPDATE request on every renewal.  There is
zero reasons why non Active Directory clients can’t do similar.

I’ve also described a procedure which would allow for automated delegation
of the reverse space along with prefix delegation as well as removal of the
delegation when the prefix delegation expires.


You can go from a pre-populated PTR records to client updated PTR record and
back dependent on the client’s capabilities.  Rather than deleting on timeout
you restore the generic PTR record.

There is no reason we can’t go from kludges to a working reverse space
other than a unwillingness to try.


> Thanks,
> Jacques
> Jacques Latour – CTO
> Canadian Internet Registration Authority (CIRA)
> Tel: (613) 237-5335 ext.294 | www.cira.ca
> <image003.png>
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Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742              INTERNET: marka at isc.org

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