[AWG] further discussions of secondlife:/// (was Re: [sldev] [VWR] summary of VWR-4021 discussion from 2008-01-08 AWGroupies meeting & general hostname issues)

[dirk husemann]

Argent Stonecutter wrote:
>
> On 2008-01-12, at 10:06, Dr Scofield wrote:
>>> 3. Second alternative, do a query for either TXT or A. If you don't 
>>> get TXT, use the A record for the server.
>> how about, try A then TXT? isn't SMTP working that way?
>
> * "A query for either TXT or A" is a single operation that returns 
> both records, if they exist, in the same packet. There's no ordering.
> * SMTP uses MX, not TXT.
> * As an aside, while some broken SMTP implementations use A if they 
> can't find an MX, but they are not supposed to... if there is no MX 
> the mail is *supposed* to bounce.
nope: RFC 2821, 3.6

    Only resolvable, fully-qualified, domain names (FQDNs) are permitted
       when domain names are used in SMTP.  In other words, names that can
       be resolved to MX RRs or A RRs (as discussed in section 5) are
       permitted, as are CNAME RRs whose targets can be resolved, in turn,
       to MX or A RRs.
      

and same, 5:

    The lookup first attempts to locate an MX
       record associated with the name.  If a CNAME record is found instead,
       the resulting name is processed as if it were the initial name.  If
       no MX records are found, but an A RR is found, the A RR is treated as
       if it was associated with an implicit MX RR, with a preference of 0,
       pointing to that host.

MX is given precedence, though. so, i guess by the same reasoning TXT should be given precedence.

	cheers,
	dirk


-- 
dr dirk husemann, pervasive computing, ibm zurich research lab
--- hud at zurich.ibm.com --- +41 44 724 8573 --- SL: dr scofield

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