> > I don't suppose use of EDNS0 would serve as a suitable
> > alternative distinguishing criterion for whether to add v6
> > glue records to replies?
>
> The issue is not the vintage of the resolver -- it is a UDP
> datagram length problem. We assume a much larger v6 datagram
> can get through without the risk of fragmentation. Such a v6
> datagram is reasonably large at 1280 bytes. The v4 datagrams
> have much less space for v6 glue records, since we can only
> assume 512 bytes of payload before fragmentation. (The truth is
> it would probably be okay if we assumed most of the world had a
> much larger MTU even for v4. That's a whole different issue,
> though.)
IPv6 may provide a larger minimum MTU guarantee than IPv4. I
guess that also means that DNS over UDP over IPv6 can in
principle use the larger datagram size (?).
I have also heard mutterings to the effect that IPv6
implementations should be required to use EDNS0, thus, it may
also be a better distinguishing factor, and has a better
probability of making dual-stack machines aware of IPv6 RRs
should the query happen to be made over IPv4 transport.
Regards,
- Håvard
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