Syntax for Internet Hostnames

[Lawrence Chan]

Hello,

On the issue of legal characters for host names, would the underscore '_' be
properly used in a domain name like ex_ample.com?  I can understand that some
operating systems might have problem when encountering hostnames with
underscores.  But would it be OK just for the domain name portion?  Or should the
hostname rule be applicable to all the labels in a name?  Internic seems to treat
underscore as a legal character as far as they are concerned.  Please advice.

Lawrence Chan
lchan at montevino.com

Mark_Andrews at isc.org wrote:

> > I'm trying to find a simple explanation that describes the syntax of a legal
> > Internet host name.  I'm not a network administrator and found some of the
> > explanations in RFC 952 and 1123 to be confusing.
>
>         A hostname is composed of "A" - "Z", "a" - "z", "0" - "9", "-"
>         and ".".  All other characters are illegal.  Hostnames are case
>         insenitive.  e.g. "EXample.COM" == "EXAMPLE.com"
>
>         "." can only be used to seperate labels. In "example.com",
>         "example" and "com" are labels.
>
>         "-" can only be used in the middle of a label, not at the start or
>         the end of a label.  e.g. "host-20.example.com".  The following
>         are illegal "-bad.example.com", "bad-.example.com", "-.example.com".
>
>         A host name has to contain at least one letter.  This is currently
>         enforced by not allowing all numeric top level domains.
>
>         Mark
> >
> > Thanks in advance!
> >
> > --
> > Seabush
> >
> > -----------== Posted via Deja News, The Discussion Network ==----------
> > http://www.dejanews.com/       Search, Read, Discuss, or Start Your Own
> >
> >
> --
> Mark Andrews, Internet Software Consortium
> 1 Seymour St., Dundas Valley, NSW 2117, Australia
> PHONE: +61 2 9871 4742                 INTERNET: marka at isc.org