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Newbie DNS questions

In article <30g8fa$c9h@spatula.csv.warwick.ac.uk>, Ian Dickinson
<cudep@csv.warwick.ac.uk> wrote:
>In article <30f2a3$asj@babs.nsr.hp.com>, cricket@hp.com writes:
>>: 2. IS "_" valid in a hostname, for example is the name
>>: road_runner.acme.com a valid name?
>>I believe so, but I've been a bit weak on valid domain names recently.
>
>It's valid as far as pure Internet stuff is concerned, but seems to break
>a number of X.400 gateways.  It's much safer to only use alphanumerics and
>hyphen, and that won't break anything anywhere that I'm aware of.

I hesitate to contradict two people whose opinions I respect as much
as Ian and Cricket, but, well, are you sure?

RFC-952 seems fairly clear to me.

   1. A "name" (Net, Host, Gateway, or Domain name) is a text string up
   to 24 characters drawn from the alphabet (A-Z), digits (0-9), minus
   sign (-), and period (.).  Note that periods are only allowed when
   they serve to delimit components of "domain style names". (See
   RFC-921, "Domain Name System Implementation Schedule", for
   background).  No blank or space characters are permitted as part of a
   name. No distinction is made between upper and lower case.  The first
   character must be an alpha character.  The last character must not be
   a minus sign or period.  [...]

RFC-1123 references this definition, and modifies it slightly: the first
character may now be a numeric character (as in 1776.com, for example).

Although BIND will happily handle names with underscores, dnswalk picks
up the error.

[ I'm slightly puzzled by the 24 character restriction.  Although
RFC-1123 states that host software should handle names up to 255
characters, it doesn't explicitly say that this is a modification to
RFC-952. ]

Tim.
--
Tim Goodwin        | "Any time *anything* goes wrong on a
Public IP Exchange | PC, I immediately suspect a hardware
Cambridge, UK      | problem :-)." -- Chris Torek

Original headers:

From: tim@pipex.net (Tim Goodwin)
Newsgroups: comp.protocols.tcp-ip.domains
Subject: Re: Newbie DNS questions
Date: 19 Jul 1994 18:06:50 +0100
Organization: PIPEX, 216 Science Park, Cambridge, England
Message-ID: <30h17a$9d0@relay2.pipex.net>
References: <1994Jul18.222849.13206@zodiac.cca.rockwell.com>
  <30f2a3$asj@babs.nsr.hp.com> <30g8fa$c9h@spatula.csv.warwick.ac.uk>

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