[dns-operations] about the underline in hostname

Paul Vixie paul at redbarn.org
Fri May 30 02:25:15 UTC 2014

Mark Andrews wrote:
> In message <5387E556.5070902 at arcor.de>, hua peng writes:
>> 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
>> what RFC item is it influenced by?
>> Thanks.
> RFC 952, RFC 1123 and RFC 1034.  Now if aa_bb.google.com is not a
> host you can turn the check off but 99.9999% of the time the owner
> name of a A record is being used as a hostname.

mark, it's ok, the joke's over. anyone who wants to enforce RFC 952 in
their gethostbyname() libc call should feel free, but, the time to try
to enforce this in any part of DNS was maybe 1995 and probably not even

we can't righteously complain about middleboxes that think they know
what UDP/53 payloads have to look like and thus prevent EDNS from being
widely deployed, while at the same time saying that BIND's zone file
parser knows what a host name ought to look like (even if you're right
99.9999% of the time).


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