good address will not resolve in freebsd (_ in host names)
Mark.Andrews at isc.org
Mark.Andrews at isc.org
Tue Oct 7 15:44:54 PDT 2003
> 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:
das_runt.shackspace.com is a illegal hostname.
> Matthew George
> SecureWorks Technical Operations
> freebsd-stable at freebsd.org mailing list
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Mark Andrews, Internet Software Consortium
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742 INTERNET: Mark.Andrews at isc.org
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