Path: utzoo!utgpu!watserv1!watmath!att!ucbvax!ralvmm.vnet.ibm.com!dmbarton
From: dmbarton@ralvmm.vnet.ibm.com ("Daniel M. Barton")
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Underscores
Message-ID: <9103022255.AA04928@ucbvax.Berkeley.EDU>
Date: 2 Mar 91 21:35:49 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Distribution: world
Organization: The Internet
Lines: 32

> Hi,
>   I've been getting complaints about my SMTP rejecting mail from sites
> with a underscore in its host name. If I read RFC 821 correctly, names
> may consist of letters, digits, and hyphens. Has this been liberalized
> recently?
>   The site in question is: its_gate.cc.uow.edu.au
>
>                                  Thanks,
>                                    Jeff

RFC 821 and 822 weren't very clear on what characters a hostname could
contain.  RFC 952, "DOD Internet Host Table Specification" clarifies
what characters are legal.  The legal characters are letters, numbers,
and the hyphen, and the hostname must begin with a letter, and end with
a letter or digit.  The exact syntax is:

<hname> ::= <name>*("."<name>)
<name>  ::= <let>(*(let-or-digit-or-hyphen>)<let-or-digit>>

Note:  I used parentheses instead of square brackets (none on my
       terminal...)

Daniel

========================================================================

Daniel M. Barton
TCP/IP Development
IBM Research Triangle Park, NC

Internet:  dmbarton@ralvmm.vnet.ibm.com
           dmbarton%ralvmm@vnet.ibm.com