[80889] in North American Network Operators' Group
Re: Underscores in host names
daemon@ATHENA.MIT.EDU (Mark Andrews)
Tue May 17 21:08:36 2005
Date: Wed, 18 May 2005 11:08:03 +1000 (EST)
From: Mark Andrews <Mark_Andrews@isc.org>
To: nanog@merit.edu
In-Reply-To: <1116377042.592906.137650@g44g2000cwa.googlegroups.com>
Cc:
Errors-To: owner-nanog@merit.edu
In article <1116377042.592906.137650@g44g2000cwa.googlegroups.com> you write:
>Hello all.
>We have a client containing an underscore in the email address domain
>name. Our email server rejects it because of it's violation of the RFC
>standard. This individuals claim is that he doesn't have problems
>anywhere else and if this is going to be a problem he's "going to take
>his business elsewhere"!
>
>I understand it's a violation of the standard, but does it pose a
>security hole to the email server to allow this sort of mail?
>
>Thanks
>
RFC 952 and RFC 1123 describe what is currently legal
in hostnames.
Underscore is NOT a legal character in a hostname.
Before anyone says that domain names allow underscore which
they do.
RFC 1034 Section 3.3
For hosts, the mapping depends on the existing syntax for host names
which is a subset of the usual text representation for domain names,
together with RR formats for describing host addresses, etc. Because we
need a reliable inverse mapping from address to host name, a special
mapping for addresses into the IN-ADDR.ARPA domain is also defined.
Mail domains follow the same rules as for hostnames. RFC
821 and its replacement RFC 2821 havn't extended the syntax
to include underscores.
Mark