Allow underscores in DNS names

[M. Warner Losh]

In message: <xzp4r5ljitl.fsf at flood.ping.uio.no>
            des at ofug.org (Dag-Erling Smørgrav) writes:
: "M. Warner Losh" <imp at bsdimp.com> writes:
: > When this has come up in the past, it was decreed that _ is a bad bad
: > bad bad idea, even though people want it.  You might want to check the
: > ancient archives (1998?) for all the reasons why.
: 
: Arguments presented in ancient archives are not necessarily relevant
: five years later.

True.  However, they are still relevant today.  '_' is illegal in DNS
names, is rejected by the majority of hosts on the internet and
generally is a bad idea.  If you do it, make it optional.

Warner