Re: Help test softupdates journaling (SUJ)

On Jan 18, 2010, at 2:18 PM, Rink Springer wrote:
>> Because DNS hostnames can't contain underscores... ?
> 
> That is false, they can (in fact, SVR records depend on this). However,
> Jeff's blog is at http://jeffr-tech.livejournal.com/; his username
> appears to be 'jeffr_tech'.

Underscores appear in SRV records for the explicit purpose of not conflicting with any valid hostname:

   The format of the SRV RR

   Here is the format of the SRV RR, whose DNS type code is 33:

        _Service._Proto.Name TTL Class SRV Priority Weight Port Target

   Service
        The symbolic name of the desired service, as defined in Assigned
        Numbers [STD 2] or locally.  An underscore (_) is prepended to
        the service identifier to avoid collisions with DNS labels that
        occur in nature.

...from http://www.ietf.org/rfc/rfc2782.txt.  See http://www.ietf.org/rfc/rfc952.txt

   1. A "name" (Net, Host, Gateway, or Domain name) is a text string up
   to 24 characters drawn from the alphabet (A-Z), digits (0-9), minus
   sign (-), and period (.).

...which was slightly modified by http://www.ietf.org/rfc/rfc1123.txt

   2.1  Host Names and Numbers

      The syntax of a legal Internet host name was specified in RFC-952
      [DNS:4].  One aspect of host name syntax is hereby changed: the
      restriction on the first character is relaxed to allow either a
      letter or a digit.  Host software MUST support this more liberal
      syntax.

Regards,
-- 
-Chuck