Subject: [SIP] Using Request-URI

From: Dvir Oren <[email-masked]>
Date: Tue, 25 Jul 2000 16:32:31 +0300 (IDT)

Should a User-Agent assume that the Request-URI used to get to it
would be 'good enough' to be used in a Contact or Record-Route?  Or
should it somehow know of its own identity and use that at the risk of 
having an unreachable hostname?

-- 
Dvir Oren               <[email-masked]>
Lucid VON Ltd.     <http://www.lucidvon.com>
9 Saloniki St.,        Tel-Aviv       Israel
Tel:  +972 3 644 3038  Fax:  +972 3 644 3039

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From: "Jo Hornsby" <[email-masked]>
Date: Tue, 25 Jul 2000 16:42:50 +0100

> having an unreachable hostname?

In my arrogance, I would consider a User-Agent that didn't know
its own Contact address to be slightly poor.

If you're trying to legislate against NATs screwing things up,
as Jonathan has already pointed out, Contact is just the Tip
of the Iceberg.  A UA needs a lot more help; from a proxy
talking to an ALG, for example.

 - Jo.

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From: Dvir Oren <[email-masked]>
Date: Tue, 25 Jul 2000 22:22:09 +0300 (IDT)

> its own Contact address to be slightly poor.

This is not the point.  How I know myself may not be the same as how
my proxy knows me.

I may have a machine with a hostname that cannot be found in the DNS.
If my SIP UA will decide to put a Contact field based on a
gethostbyname(), for example, it will assist no one since my host name 
is not a valid hostname.

However, my proxy can reach me through some hostname that is valid and 
that the proxy knows it, but I don't, for some reason.

This is why I thought of using the Request-URI instead of trying to
figure out my own Contact, which may lead me to results that my proxy
can't handle.

It seems to me that if the Request-URI got to me, using it as a
Contact field will also get to me.

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From: Rohan Mahy <[email-masked]>
Date: Tue, 25 Jul 2000 16:52:32 +0200

>that the proxy knows it, but I don't, for some reason.

It seems reasonable to check your own "hostname" in DNS before you give it
out to someone else.  If it doesn't resolve, just use your IP address in
Contact.

	Contact: <sip:[email-masked]:5060>

thanks,
-rohan

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From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 26 Jul 2000 01:41:36 -0400

> Contact field will also get to me.

Not necessarily. Proxy routing logic can be arbitrarily complex, and it
may have forwarded it to you based on some other criteria.

The safest best for Contact is generally sip:user@IPADDRESS.

-Jonathan R.

-- 
Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
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