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