Underscores in host names

Thu May 19 16:02:35 UTC 2005

On Thu, May 19, 2005 at 12:01:54PM -0300, MARLON BORBA wrote:
> Hmm, they've always teached to me that . (dot) at the end of hostnames
> indicates the (hidden) Root domain:
>
> blah.domain.com.[Root]

This much is true.

> And my teachers always said that we don't need to write the final .
> because every domain belongs to the Root domain.

This, not so much.  Well, kinda.

Specifically, as I think was noted earlier on the thread in passing, as
well, that trailing dot is a hint *to your local name resolver* that
says "do not attempt to apply any locally defined DNS search path to
this name; look it up once, anchored to the DNS root[0], and if you get
an NXDOMAIN, believe it".

Semantically, that trailing dot, as it is presented to an application,
*is not part of the domain name*.  It's ephemeral; only existing on the
machine where you type it in -- specifically, it does not get sent in
queries (SFIAK), even if you typed it in.

So, no, you *don't* need to write it, unless you as an application user
are trying specifically to pin the name on the root... but it's
invisible to the rest of the system, just as the names themselves are
invisible to the TCP stack once you've looked them up and opened a
stream.

Cheers,
-- jra
-- 
Jay R. Ashworth                                                jra at baylink.com
Designer                          Baylink                             RFC 2100
Ashworth & Associates        The Things I Think                        '87 e24
St Petersburg FL USA      http://baylink.pitas.com             +1 727 647 1274

      If you can read this... thank a system administrator.  Or two.  --me