Date: Wed, 08 Oct 2003 08:44:45 +1000 From: Mark.Andrews@isc.org To: Matthew George <mdg@secureworks.net> Cc: freebsd-stable@freebsd.org Subject: Re: good address will not resolve in freebsd (_ in host names) Message-ID: <200310072244.h97Mij0o012523@bsdi.dv.isc.org> In-Reply-To: Your message of "Tue, 07 Oct 2003 16:01:23 -0400." <20031007155846.J25531@localhost>
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> On Tue, 7 Oct 2003, Andi Hechtbauer wrote: > > > Just FYI, > > > > Restrictions on hostname character sets seem obsoleted by this: > > > > >From RFC2181, Section 11 > > > > [...] any binary string whatever can be used as the label of any > > resource record. Similarly, any binary string can serve as the > > value of any record that includes a domain name as some or all of > > its value (SOA, NS, MX, PTR, CNAME, and any others that may be > > added). Implementations of the DNS protocols must not place any > > restrictions on the labels that can be used. In particular, DNS > > servers must not refuse to serve a zone because it contains labels > > that might not be acceptable to some DNS client programs. [...] > > > > Regards, > > Andi > > > > > > underscores are part of the SRV RR spec for services and protocols ... > > from RFC 2782: > > The format of the SRV RR > > Here is the format of the SRV RR, whose DNS type code is 33: > > _Service._Proto.Name TTL Class SRV Priority Weight Port Target > > (There is an example near the end of this document.) And the underscores were choosen here so THAT THE SERVICE NAME AND PROTOCOL NAME WOULD NOT CLASH WITH A HOSTNAME. This allows for the to be a "tcp" delegation and a "_tcp" service. Yes I actually worked for a organisation which had a "tcp" sub- domain (Tropical Crops and Pastures). The restriction on underscores comes from RFC 952 and its predecessors. It predates the creation of the DNS. A similar restriction also applies to mail only domains. RFC 2181 has no impact on consumers of DNS data. In fact it says consumers of DNS data are free to impose any other additional restrictions they want. The get*() library routines are consumers of DNS data. The best thing you can do when you see a hostname with a underscore in it is to inform them that they have a bad name. Names with underscores in them are not common. Failure to inform a site about a known broken configuration does them a disservice. Even Microsoft tried to do the right thing by using a underscore to seperate off the active directory heirachy. Steven this was brought about by the following: http://das_runt.shackspace.com/techtv-blooper.wmv das_runt.shackspace.com is a illegal hostname. Mark > -- > Matthew George > SecureWorks Technical Operations > > _______________________________________________ > freebsd-stable@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-stable > To unsubscribe, send any mail to "freebsd-stable-unsubscribe@freebsd.org" -- Mark Andrews, Internet Software Consortium 1 Seymour St., Dundas Valley, NSW 2117, Australia PHONE: +61 2 9871 4742 INTERNET: Mark.Andrews@isc.org
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