On 2008-04-04 17:30:29 -0400, Robert A. Rosenberg wrote: > At 12:56 -0400 on 04/04/2008, Tony Hansen wrote about Re: current > usage of AAAA implicit MX?: > > >These questions are intended to find out what current IPv6 deployments > >do in these situations. When an MX is not found, are they already > >looking for both A and AAAA records, or are they only looking for A > >records. Are they following RFC 3974 or not? What's the installed base > >already doing? > > RFC 3974 talks about Dual Stack set-ups and what an IPv4-Only Server > should do when presented with a Mixed MX or an MX that only points at > IPv6 AAAA records. It, BTW, REQUIRES an MX if there are any IPv6 MTAs > and only supports A-Fallback in the absence of an MX
No.
> (ie: It does NOT define any attempt to look for AAAA records in the
> absence of an MX after/before checking for A records).
Yes, it does:
| (1) Lookup the MX record for the destination domain.
[...]
| If NODATA (i.e., empty answer with NOERROR(0) RCODE) is
| returned, there is no MX record but the name is valid. Assume
| that there is a record like "name. IN MX 0 name." (implicit MX)
| and go to step (3).
[...]
| (3) If the sending MTA has IPv4 capability, lookup the A records.
| Keep the resulting addresses until step (5).
|
| (4) If the sending MTA has IPv6 capability, lookup the AAAA records.
Both A and AAAA records are looked up for the implicit MX.
> It also states that in the presence of an MX containing IPv6 address
> references, an IPv4-Only stack should ignore the IPv6 addresses
Yes, of course. It cannot reach them anyway. Just as IPv6-only hosts can
ignore A records since they cannot reach them either.
> and only use the IPv4 addresses (and in a IPv6-Only MX to NOT do
> IPv4-A-Record fallback).
Where do you read that?
hp
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