Re: Underscore in IIS 6 Host Header definition
From: srock (user_at_localhost)
Date: 11/20/04
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Date: Fri, 19 Nov 2004 19:33:34 -0500
The RFC that you referenced does not define the standard for the DNS
protocol, valid host names, or anything - it's just an admin guide that is
widely regarded as outdated. An underscore is not valid in a host. I found
this while going through the 100's of posts that says an underscore is not
legal:
From: http://www.acmebw.com/askmrdns/archive.php?category=81&question=604
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~
The skinny on the dreaded underscore character
> This one has long since troubled me but given Bill Gates' decision to
> (finally) move towards DNS resolution - seems to be more frequent
occurrence
> - obviously some characters are illegal but what's with DNS and the
> underscore character? If entered in a hosts file, its valid - machines
> names can have it and it appears some versions of DNS can use the
> underscore without problems yet others can't - what's the deal?
Just to be clear, underscore has *NEVER* been legal as a hostname character.
Never. To this day it is still not legal. RFC 952 and RFC 1123 state the
rules. Nevermind that it is legal in NetBIOS names. Nevermind that many Unix
vendors tell you it is legal in their instructions for setting the hostname.
Some people reject names with underscores in them at the DNS server because
there's an option for it. That option exists because of some hoopla about
root exploits in badly behaving applications that blindly pass the results
of PTR lookups to other system calls. However, DNS servers were not designed
to enforce hostname rules. Those rules should be enforced at the client, so
the default setting on servers is to allow all characters through. That's
the skinny on underscores.
FYI, if you stick with the legal Internet *hostname* character set, you'll
never run into problems.
-- Mr. DNS VeriSign Global Registry Services mr-dns@verisign.com http://www.acmebw.com/askmrdns/ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~ That post really sums it up. Seth "Aaron" <Aaron@discussions.microsoft.com> wrote in message news:A013A91E-C36C-4785-90E4-2513E67A8B58@microsoft.com... > MS DNS allows underscore but IIS Host Headers do not, I just wondered if > there was a good reason...nothing spitefull intended. If the standards in > this case are not clear, then I see no rational reason for the inconsistancy. > > > Thanks for response, > > Aaron > > > "David Wang [Msft]" wrote: > > > Hehe... what do you expect when RFCs, designed by public and unbiased > > entities, do not agree nor fully flesh out details... are MS products > > supposed to follow RFC and not work with each other, or not follow RFC and > > work with each other but get blamed for not following standards. Or some > > confused muddle in between, which makes everyone mad. > > > > Hmm, it is no-win either way -- I think people just want to irrationally > > blame Microsoft... > > > > -- > > //David > > IIS > > This posting is provided "AS IS" with no warranties, and confers no rights. > > // > > "Aaron" <Aaron@discussions.microsoft.com> wrote in message > > news:B1AB464A-22A4-440E-B868-76DFCF55232B@microsoft.com... > > Thanks for the ideas Seth. I'm not satisfied with the answer though. We've > > had underscore in local host names for quite some time, before we switched > > to > > AD and MS DNS. Its interesting to note the RFC's don't seem to agree, and > > neither do MS' products. We won't use underscore going forward however, > > dashes will work just fine also. > > > > Aaron > > > > "srock" wrote: > > > > > An underscore is not valid in host names. Microsoft removed support in IIS > > 6 > > > for the underscore in host headers because it's not valid. You can edit > > the > > > server binding manually to get it to 'work' if you really want to do > > > something non-standard. If I were you, I'd spend the time to rename the > > > site(s) in question. > > > > > > just do a google search and you'll find 100's of posts saying that an > > > underscore n a host name is not valid. > > > > > > Seth > > > > > > > > > > > > > > > "Aaron" <Aaron@discussions.microsoft.com> wrote in message > > > news:955DAF21-9210-4EA8-85A9-AC110FB4EDFE@microsoft.com... > > > > Thanks for checking that Seth. In RFC1033, the DNS Admin Guide it states > > > > otherwise...any 8 bit character but specifically mentions underscore. > > > Since > > > > the RFC's are guidlines, who is right? I'm of the thinking that since MS > > > DNS > > > > lets you use underscore in host name records, why wouldn't their own web > > > > server allow them? > > > > > > > > Excerpt from RFC1033: > > > > > > > > NAMES > > > > > > > > A domain name is a sequence of labels separated by dots. > > > > > > > > Domain names in the zone files can be one of two types, either > > > > absolute or relative. An absolute name is the fully qualified domain > > > > name and is terminated with a period. A relative name does not > > > > terminate with a period, and the current default domain is appended > > > > to it. The default domain is usually the name of the domain that was > > > > specified in the boot file that loads each zone. > > > > > > > > The domain system allows a label to contain any 8-bit character. > > > > Although the domain system has no restrictions, other protocols such > > > > as SMTP do have name restrictions. Because of other protocol > > > > restrictions, only the following characters are recommended for use > > > > in a host name (besides the dot separator): > > > > > > > > "A-Z", "a-z", "0-9", dash and underscore > > > > > > > > > > -------------------------------------------------------------------------- > > > > "srock" wrote: > > > > > > > > > An underscore is not valid in host names. See section 2.3.1 of RFC > > 1035: > > > > > http://www.faqs.org/rfcs/rfc1035.html > > > > > > > > > > Seth > > > > > > > > > > "Aaron" <Aaron@discussions.microsoft.com> wrote in message > > > > > news:54FB41BF-65FE-4D5D-B553-5A232B669F79@microsoft.com... > > > > > > Underscore (_) is perfectly valid in DNS, so why is it disallowed in > > > the > > > > > IIS > > > > > > Host Header definition? It seems that the validation in IIS 6 only > > > allows > > > > > > A-Z, a-z, '.', and '-'. Why not '_'? > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > >
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