[dns-operations] about the underline in hostname

[hua peng]

IIRC BIND doesn't permit an A record whose label has a underscore 
included, for example, this one:

aa_bb.google.com.         300     IN      A       74.125.128.106

what RFC item is it influenced by?
Thanks.


> BIND does allow domain names with underscores in them. In fact SRV records use underscores so that names with those _service._proto labels can't be confused with hostnames.