On Wed, 26 Mar 2008, Jim Fenton wrote: >> I keep trying to understand why the SMTP use of AAAA records should be any >> different than its use of A records. Haven't heard a solid explanation, >> nevermind seen consensus forming around it. > > It seems there are two ways of looking at this: > > (1) AAAA records in the IPv6 world should do exactly same things as A > records in the IPv4 world, so SMTP should look for an AAAA record in the > absence of an MX record, just as A records are used in the absence of MX > records. > > (2) Although some SMTP servers will continue to be found through A > records for legacy reasons, there is no longer a good reason for any new > server not to have a published MX record. SMTP clients (senders) will, > of course, need to continue to look up A records, but since there is > currently no significant use of AAAA records for email routing, we > should not perpetuate this legacy in IPv6 as it is in IPv4. > > These are both reasonable positions, but I'm in camp (2). The > additional use of AAAA records for email address resolution would add > complexity to at least some implementations and test cases, and it > something that should never be needed: v6 mail handlers will just > publish MX records. There is probably a small DNS efficiency argument > as well, especially if the MX, A, and AAAA requests are not made together. I agree with Jim's characterization and IMHO both positions are reasonable. I also prefer (2) because I don't think the original "A fallback" was meant to stay there very long and we just never got around to deprecating that feature. If you ask a random sampling of postmasters and DNS domain owners, I doubt many would even remember right off the bat that such a fallback exists. Further, given that the feature in and of itself does not provide any additional value, I don't see why the practise should be propagated to IPv6. But if the majority were to favour (1), that would be fine with me as well. Additionally I believe this is not an issue we as the IETF should get stuck at for a longer period. Reaching closure, whichever decision it is, in the timescale of a couple of months, is IMHO better than a very strong consensus on the approach. -- Pekka Savola "You each name yourselves king, yet the Netcore Oy kingdom bleeds." Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings _______________________________________________ IETF mailing list IETF@xxxxxxxx https://www.ietf.org/mailman/listinfo/ietf