Subject: [dnsext] Question on characters in DNS lookups?

From: Nicholas Weaver <[email-masked]>
Date: Fri, 4 Mar 2011 07:37:37 -0800

Just to confirm, although hostnames are restricted, any octet may be used in a label for lookups of non-hostname records (eg, TXT records).

	Correct?

	If so, which RFC includes this?

---

From: Stephane Bortzmeyer <[email-masked]>
Date: Fri, 4 Mar 2011 16:42:57 +0100

On Fri, Mar 04, 2011 at 07:37:37AM -0800,
 Nicholas Weaver <[email-masked]> wrote 
 a message of 10 lines which said:

> 	Just to confirm, although hostnames are restricted, any octet
> 	may be used in a label for lookups of non-hostname records
> 	(eg, TXT records).
> 
> 	Correct?

Yes.
 
> 	If so, which RFC includes this?

RFC 2181, section 11
RFC 1035, section 2.3.1

---

From: Mark Andrews <[email-masked]>
Date: Sat, 05 Mar 2011 09:05:31 +1100

> > 	may be used in a label for lookups of non-hostname records

More correctly the DNS does not place restrictions.  The DNS is
a storage device.  The users of the DNS may place restrictions.

Hostnames have restrictions RFC 952.
Mail domains have restrictions RFC 822 and its successors.
 
> _______________________________________________
> dnsext mailing list
> [email-masked]
> https://www.ietf.org/mailman/listinfo/dnsext
-- 
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: [email-masked]

---

From: Edward Lewis <[email-masked]>
Date: Sat, 5 Mar 2011 10:45:54 -0500

>Mail domains have restrictions RFC 822 and its successors.

Mark,

What's your take on this:

In some places an RR's RDATA needs a domain name and in some places 
it calls for a host name.  The value of CNAME record is a domain 
name.  The value of an NS record is a host name.  The "target" of an 
MX record is a host name.

The difference in these three cases is - in a CNAME the target is a 
location in the tree, not a host.  For a NS, the target is a host but 
one that is being accessed by DNS implementations.  For the latter, 
the MX, the target is a host to be contacted by a SMTP implementation 
- which seem to be quite finicky things when it comes to host syntax.

In light of this, I choose to limit the RDATA of MX records to host 
name rules, and NS too for convenience but let the CNAME be any 8-bit 
value.

The original question mentioned questions - the owner name in a 
question (and all sections) can have any 8-bit value.  I'm asking if 
you think there should be restrictions on what's in RDATA.

I checked STD 13 and found this, this is where I got my idea years ago:

#                CNAME           a domain name.
#
#                MX              a 16 bit preference value (lower is
#                                better) followed by a host name willing
#                                to act as a mail exchange for the owner
#                                domain.
#
#                NS              a host name.

In this case, the NS is said to be a host, not domain, name. From 
that, I would say that the DNS does place restrictions - but only 
within some RDATA specifications.

-- 
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Edward Lewis             
NeuStar                    You can leave a voice message at +1-571-434-5468

Me to infant son: "Waah! Waah! Is that all you can say?  Waah?"
Son: "Waah!"

---

From: Masataka Ohta <[email-masked]>
Date: Sun, 06 Mar 2011 09:57:21 +0900

> # CNAME a domain name.

For an example, see RFC2317, a BCP.

					Masataka Ohta

---

From: Edward Lewis <[email-masked]>
Date: Mon, 7 Mar 2011 09:11:34 -0500

>For an example, see RFC2317, a BCP.

Hmmph.  A case of a BCP recommending actions in "violation" of a 
standards track document.

Interesting catch...;)

---

From: Edward Lewis <[email-masked]>
Date: Mon, 7 Mar 2011 09:13:32 -0500

D'oh!!!

Not in violation - it's what is recommended.

Gotta stop writing email while watching TV.