On topic of domains

Thu Jul 11 22:57:59 UTC 2013

Mark Andrews <marka at isc.org> writes:

> In message <krmkg2$flc$1 at ger.gmane.org>, Chris Hills writes:
> > Whilst I am not a fan of dotless domains, as long as one uses the fully
> > qualified domain name (e.g. http://ac./), there should not be any
> > trouble using it in any sane software. It seems that most people aren't
> > aware these days that a fqdn includes the trailing period (by definition).
> 
> No it does not.  Period at the end is a local convention to stop
> searching on some platforms.  It is not syntactically legal.  Note
> the words 'a sequence of domain labels separated by "."'.  Periods
> at the end are NOT legal.
> 
> RFC 1738
> 
>     host
>         The fully qualified domain name of a network host, or its IP
>         address as a set of four decimal digit groups separated by
>         ".". Fully qualified domain names take the form as described
>         in Section 3.5 of RFC 1034 [13] and Section 2.1 of RFC 1123
>         [5]: a sequence of domain labels separated by ".", each domain
>         label starting and ending with an alphanumerical character and
>         possibly also containing "-" characters. The rightmost domain
>         label will never start with a digit, though, which
>         syntactically distinguishes all domain names from the IP
>         addresses.

That was fixed in RFC 2396:

      host          = hostname | IPv4address
      hostname      = *( domainlabel "." ) toplabel [ "." ]

   ... The rightmost
   domain label of a fully qualified domain name will never start with a
   digit, thus syntactically distinguishing domain names from IPv4
   addresses, and may be followed by a single "." if it is necessary to
   distinguish between the complete domain name and any local domain.

However, I think it's safe to say this is an edge case and chances are
you'll have trouble using dotless domains with some software and
processes.  For example, you'll probably have trouble getting a SSL
certificate.