Subject: [dns-dir] long TLD names

From: Jari Arkko <[email-masked]>
Date: Mon, 25 Jul 2011 14:58:21 -0400

I got a question from Elise at the IETF-IANA team today about the impact 
of increasing the length of the TLDs to potentially up to 63 bytes, as 
ICANN is going to allow these.

The question was whether there are any IETF specifications that are 
affected. My guess was that the answer is no, all potential problems are 
in the implementions. But you would know this better. What does the DNS 
directorate say?

Jari

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From: Olafur Gudmundsson <[email-masked]>
Date: Mon, 25 Jul 2011 15:02:35 -0400

> in the implementions. But you would know this better. What does the DNS
see:
	 http://tools.ietf.org/html/draft-liman-tld-names-05

Short answer is no specification issue, only application concerns, thus 
the rules that are being proposed in there.

	Olafur

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From: Patrik Fältström <[email-masked]>
Date: Mon, 25 Jul 2011 21:14:11 +0200

On 25 jul 2011, at 20.58, Jari Arkko wrote:

> I got a question from Elise at the IETF-IANA team today about the impact of increasing the length of the TLDs to potentially up to 63 bytes, as ICANN is going to allow these.
> 
> The question was whether there are any IETF specifications that are affected. My guess was that the answer is no, all potential problems are in the implementions. But you would know this better. What does the DNS directorate say?

I would agree with this, but we do know there where problems with .MUSEUM and other TLDs that broke the 3-char limit. I do not remember any application layer protocol that have a limit that is more restrictive than that.

One should check DN definitions in X.509...I vaguely remember problems with OpenSSL when I had to generate new cert for a server that had a total length of a domain name that was "too many characters" (that was surprisingly low, definitely lower than 63 characters). I can not find the blog entry where I wrote about it though... :-(

Of course, it is important one count the number of characters in an A-label.

   Patrik

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From: Peter Koch <[email-masked]>
Date: Mon, 25 Jul 2011 21:23:42 +0200

> in the implementions. But you would know this better. What does the DNS 

it is unclear what (applications) protocols assume about domain names and
their lengths, but the last authoritative word is in RFC 1123:

      Host software MUST handle host names of up to 63 characters and
      SHOULD handle host names of up to 255 characters.

So, in theory you could hit the boundary of a piece of software that
is within the boundaries of the MUST, but outside teh SHOULD and thus
would be unable to process anything but the top label.  In practice,
I doubt this is going to happen - but no oath.
Also, the 63 label length is for the on-the-wire format!

-Peter

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From: Lars-Johan Liman <[email-masked]>
Date: Mon, 25 Jul 2011 16:34:21 -0400

> Also, the 63 label length is for the on-the-wire format!

Hmm. Interesting. I must check up on that. Especially: how does RFC 1123
(as opposed to other docs) define "hostname" - FQDN or first label, or
not at all?

So ... I think Elise is interested in the TLD-label specifically, not
hostnames. Of course, the math around the TLD has effects on the FQDN as
well, so it becomes even worse, but it's kind of hopeless if we're going
to take every application on the planet into account. X.509 is indeed an
important structure to take into account, but who is going to make the
call in the gray zone?

I think the IANA should have a liberal policy, but add a "note well"
statement that says "long TLDs may lead to problems at the other end of
the domain name ... - you have been warned!". In all honesty, it's not
IANA's (nor the IETF's) fault that people choose to make bad
implementations, by making the implementation judgement "I'll stick to
the MUST, and ignore the SHOULD". That is a conscious decision to limit
oneself at the risk of being incompatible with other players.

I say 63 octets per label, and 255 for the total length are the limits
that should be applied - TLD label or not. YMMV.

(I have a distinct feeling that a big black ugly furry creature wearing
T-shirt that says "Now is the time to clarify all the mess from the '80s
with inconsistent and unclear DNS sytnax definitions.", is lurking over
_my_ shoulder ... Anyone want to trade places? ;-)

				Cheers,
				  /Liman
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