To:
perry@wasabisystems.com
Cc:
randy@psg.com, seamus@bit-net.com, users@ipv6.org, dnsop@cafax.se, ngtrans@sunroof.eng.sun.com
From:
Havard Eidnes <he@runit.no>
Date:
Sat, 20 Jan 2001 16:46:38 +0100
In-Reply-To:
Your message of "19 Jan 2001 19:27:28 -0500"<87lms7f4pb.fsf@snark.piermont.com>
Sender:
owner-dnsop@cafax.se
Subject:
Re: IPv6 dns
> > 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