Domain concept?

[Chris Turner]

Sdävtaker wrote:

> Can u please point me to some place with a nice explanation? I am
> googling it but only find some technical stuff about them and no the
> concept involved.
> Thanks for any help
> Sdäv

The main hints comes from resolver(5):

-8<-
On a normally configured system this file should not be necessary.  The
only name server to be queried will be on the local machine, the domain
name is determined from the host name, and the domain search path is
constructed from the domain name.
. ..
If no nameserver entries are present, the default is
to use the name server on the local machine.
. ..
Local domain name.  Most queries for names within this domain
can use short names relative to the local domain.  If no
domain entry is present, the domain is determined from the
local host name returned by gethostname(3); the domain part
is taken to be everything after the first `.'.
. ..
Search list for host-name lookup.  The search list is nor-
mally determined from the local domain name; by default, it
contains only the local domain name.  This may be changed by
listing the desired domain search path following the search
keyword with spaces or tabs separating the names.
->8-

Most of this documentation goes back to the original resolver
manual page (from 4.2BSD or 4.3BSD, I forget)- I was confused about this
issue myself & did the research :)

It looks like originally, the expectation was to run named
locally & have your hostname-implied search path match your
DNS topology - still probably a good idea today..

If you think of the machines at the time this page was probably written
('84 or so), your site would probably be running a timesharing mini
directly on the Internet rather than a lan workstation so this makes sense..

Unfortunately nowhere that I know of in the (manual page) documentation
does it directly say "Set your hostname to your FQDN and run named", so
you have to kind of scratch around to understand the assumption..

It also makes it mildly harder to stop SMTP relaying with some
mail servers if you don't set to FQDN.