Subject: Re: TXT records, are they alive?

From: Greg Hudson <[email-masked]>
Date: 12 Apr 2003 10:40:37 -0400

On Sat, 2003-04-12 at 02:08, Mohammad Awad wrote:
> 1- Is the TXT record still considered a standard and is it really 
> implemented in nowadays server?

Yup.  They've worked fine in BIND for a while.  (On the server side,
there's been some issue about how much control a zone file has over the
boundaries between the text labels.  I don't know the status of that.)

> 2- if yes, do the servers really respond to queries that necessitate 
> searching inside the RDATA cell of that TXT records?

I'm not quite sure what you're asking here.

At MIT, we use them for Hesiod records, which isn't necessarily the
cleanest use of the DNS, but it works well.  Dig for something like
ghudson.passwd.ns.athena.mit.edu txt for an example.

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From: Derek Atkins <[email-masked]>
Date: 12 Apr 2003 10:40:50 -0400

"Mohammad Awad" <[email-masked]> writes:

> Hi all,
> I'm doing some research that I'll get it dependant on the TXT record
> in RFC1464 of 1993. I've noticed that there was no further drafts,
> RFCs, nor comments about that RR.

Why should there be?  It works fine, and no problems have been found
requiring an update to the draft.

> So:

Uh, most definitely.  As far as I can tell just about every DNS Server
and resolver around nowadays supports TXT records.  Hesiod wouldn't
work without it.

> searching inside the RDATA cell of that TXT records?

No -- at least not that I've seen.  The servers only look at the name,
not the rdata, when looking up a response.  This is as it should be in
general.

> Thank you all
> Moh Awad

-derek

-- 
       Derek Atkins
       Computer and Internet Security Consultant
       [email-masked]             www.ihtfp.com

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From: Peter Koch <[email-masked]>
Date: Sat, 12 Apr 2003 18:14:16 +0200

> I'm doing some research that I'll get it dependant on the TXT record in 
> RFC1464 of 1993. I've noticed that there was no further drafts, RFCs, nor 
> comments about that RR.

The TXT RR was not introduced by RFC 1464. It's only the idea of internal
structure (tag/value) that was promoted by this document.

> implemented in nowadays server?

Since the TXT RR was part of the initial DNS RFCs it's part of the DNS
standard. RFC 1464 however has "Experimental" status. You can find out the
difference in BCP 9/RFC2026.
Not only do servers implement the TXT RRs, but also resolvers support it.
TXT RRs are not really in widespread use today unless for locally focused
purposes (e.g. hesiod). Within "DE", a TLD with > 6 million names and
more than 4.5 million zones, there are roughly 150000 TXT RRs and only
some in the low hundreds use the RFC 1464 notation, mostly to ``advertise''
ethernet addresses. Some others are used to support the RP RR defined in
RFC 1183.

> searching inside the RDATA cell of that TXT records?

RFC 1464 did not suggest specific server behaviour. Instead, the resolver
or some function between application and resolver would have to extract
the information based on the selected attribute.
There's no other way because there is currently no query type or opcode
which could take into account partially available RDATA (i.e. return
all A RRs for foo.example.com with '10' in the first octet or return all
TXT RRs for bar.example.com with 'location=' at the beginning of RDATA.
And while it's theoretically possible to define such an opcode, it would
be in conflict with both RFC 2181, which mandates that RRSets always
be dealt with as a complete set and DNSSEC, which can only sign complete
RRSets.

-Peter

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From: Rob Austein <[email-masked]>
Date: Sat, 12 Apr 2003 13:38:33 -0400

> boundaries between the text labels.  I don't know the status of that.)

The original BIND 4.x implementation of TXT RRs treated the entire
RDATA as one big string.  If memory serves, this was fixed circa 1996.