IPv4 in IPv6 in AAAA records

Colm MacCarthaigh colm.maccarthaigh at heanet.ie
Tue Aug 24 18:33:07 UTC 2004

On Tue, Aug 24, 2004 at 12:33:43PM -0500, Phil Howard wrote:
> As such, no need exists for a unicast address space as the TRT
> proposal suggests.  The existing ::ffff can do the job, and won't have
> the risks Metz and Hagino suggest when done right.  If ::ffff goes
> over my local LAN, that's my business; there is no need for the
> redundant c6::/64 assignment for it.

You're crazy! That's like saying you can use the multicast IPv4
assignments as your own private addresses, because you never plan to use
multicast and since it's on your own LAN, it's not the rest of the
worlds business ;-)

::ffff/96 is a host-level only mechanism, it will really really confuse
your applications if they see it coming on the wire. Say you have an
application listening on ::, it gets a packet on ::ffff: ,
how does it know that wasn't an IPv4 packet that came in and was
translated by the hosts stack?

It's a bad bad idea. ::ffff/96 isn't some arbitrary handy way of
representing IPv4 address in IPv6, it's a transistion mechanism. Please
use it properly, the last thing we need is people deploying IPv6
brokenness and getting the protocol a bad rep :)

But back on-topic ...

> But in nsd-users, the on-topic issue is whether ::ffff should be
> supported in AAAA records ... specifically with dotted-quad-suffix
> syntax.  

No, ::ffff should not be treated more specially than any other 
/96 by NSD. A DNS implementation should be agnostic to the content
of an AAAA record. 

NSD should (and now does afaict) however support the dotted-quad
representation for the last 32-bits, for any AAAA record. So if I want
to have 2001:770:18:2::, I can :)

> I want to hear reasons why that should not be allowed.

It should be, but the dotted-quad thing should not be specific to
a particular prefix :)

> Whether ::ffff should be allowed in packets should be a layer 2 issue,
> not a DNS issue.  If comes to pass that there is no use for ::ffff
> then whether it works, and is convenient to use, in zonec is moot.
> But if in the end it is decided that c6::/64 is the way to go, you
> still need the dotted-quad-suffix support.

dotted-quad syntax has to be supported, I don't think that can be
disputed :)

Colm MacCárthaigh  /  HEAnet, Teach Brooklawn,  / Innealtóir Ghréasáin
+353 1 6609040    / Bóthar Shelbourne, BÁC, IE /   http://www.hea.net/

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