Subject: [SIP] 200 OK Contact, firewalls, record-route

From: David Daiker <[email-masked]>
Date: Mon, 6 Nov 2000 12:55:36 -0500 (EST)

I have a couple of questions regarding the interaction of the
contact header in the 200 OK, firewalls, and record-route
 
The spec says that a UA behind a firewall, provides the ip of the
firewall as its contact address, and if record-route headers exist,
this address is appended (by the UAC) to the route for subsequent
requests.

My question is this - what if the firewall proxy, due to some
independent feature logic, already added a record-route of itself
to the request ? Should the UAC that builds the route, verify that
the route is not already present before appending the contact address ?

Along those same lines, what should a proxy do that sees itself 
as the next route ? The spec says it should forward it unless that
will cause a loop. So, should it return a loop detected error ?,
pop that route, and forward it to the next route ?, or route
based upon the URI ?

thanks,

david

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From: Jonathan Rosenberg <[email-masked]>
Date: Tue, 7 Nov 2000 01:44:29 -0500

> -----Original Message-----
> From: David Daiker [mailto:[email-masked]]
> Sent: Monday, November 06, 2000 12:56 PM
> To: [email-masked]
> Subject: [SIP] 200 OK Contact, firewalls, record-route
> 
> 
> 

Be careful here. This treatment of Contact headers has about 1/2 sentence
mention in the spec. I guess it deserves more explanation.

The contact header sets the address where subsequent requests go. Thats it.
Now, a smart network can be set up whereby the UA inserts the address of the
firewall, and the firewall knows that this is happening, so it doesn't
record-route, and knows to translate this to something internal when
requests arrive.

In other words, this capability needs to be used in a coordinated fashion.
The proxy must know that the UA is doing something funky here. In general
usage, it should not make this assumption.

-Jonathan R.

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Jonathan D. Rosenberg                       72 Eagle Rock Ave.
Chief Scientist                             First Floor
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[email-masked]                     FAX:   (973) 952-5050
http://www.cs.columbia.edu/~jdrosen         PHONE: (973) 952-5000
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