Reverse DNS RFCs and Recommendations

Wed Oct 30 22:36:20 UTC 2013

Nolan Rollo wrote:

> RFC draft-msullivan-dnsop-generic-naming-schemes-00.txt states:
> When using IP addresses in host names, their numbers SHOULD be
>     separated by '.'s (dots) rather than any meta character such as a '-'
>     (dash) and expressed in decimal.  Host names SHOULD NOT use the '_'
>     (underscore) character, host names for hosts with any form of SMTP
>     mail service MUST NOT use the '_' (underscore) character.  It is
>     preferable to use the IP address in reverse format in the same way
>     the the IN-ADDR.ARPA. domain is defined.

That's not correct.

Not all domain names are host names, which is why '_' is allowed
for some domain names such as:

      _ldap._tcp.example.com [rfc2782]

However, though rfc1034 specifies;

   For example, when naming a mail domain, the user should satisfy
   both the rules of this memo and those in RFC-822.  When creating
   a new host name, the old rules for HOSTS.TXT should be followed.

both of "should" in the rfc should, today, be interpreted as "MUST".

						Masataka Ohta