Allow underscores in DNS names

[Louis A. Mamakos]

> 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.

Strictly speaking, the '_' is illegal in HOSTNAMES.  The DNS can contains
objects other than those used as hostnames, and the protocols support
arbitrary strings of octets which can be used as labels in DNS names.

It's the application of looking up host names using the DNS which is
in question.  And if underscore characters are so toxic in hostnames,
then why are they allowed in /etc/hosts or NIS-dervied lookups?

louie