Subject: Re: [Sipping] Question on draft-ietf-sipping-v6-transition-07

From: "Dale Worley" <[email-masked]>
Date: Wed, 03 Mar 2010 17:43:09 -0500

On Fri, 2010-02-05 at 09:03 -0600, Kevin P. Fleming wrote:
> That would in fact be wrong, domain names cannot begin with '.'. In
> addition, I'd recommend against allowing an 'invalid' name that does not
> contain '.', because many systems (including my laptop) are configured
> with default DNS search domains that are searched when names that
> contain only one component are resolved. 'invalid' in my case would
> search in at least two domains for 'invalid.xxx.yyy', which is not
> helpful in the context of this draft.
> 
> Explicitly specifying 'this.is.invalid' or something similar seems to be
> prudent in this case.

That's an interesting point.  As you note, "invalid" is a perfectly
valid DNS name that is reserved.  But it might be subject to bad
resolver behavior.  Indeed, IIRC some popular resolvers will always
search multiple configured domains unless the name given to them is
ended with an extra "." (which seems to be allowed for in the syntax).
But any SIP implementation should use its local resolver in such a way
that such additional searches are never done.

But how many SIP implementations do that correctly?

Dale