Subject: RE: [Sip] From Header

From: Anil Bollineni <[email-masked]>
Date: Mon, 23 Feb 2004 11:13:01 -0800

The Via header tells that IP address/port where the response should be sent.
It does not specify from where the request has been come, as the ports for
sending request and receiving responses can be different. I think the only
way we can tell is by seeing the sending ip and port in IP header of the
packet. Please correct if I am wrong.

Thanks,
Anil

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-----Original Message-----
From: xiao'tong liang [mailto:[email-masked]] 
Sent: Sunday, February 22, 2004 6:07 PM
To: Anil Bollineni
Subject: Re: [Sip] From Header

Via header.

--
xiaotong

--- Anil Bollineni <[email-masked]> wrote:
> Hi All,
> 
>  
> 
>       I understand from the following statement in
> RFC, that From header
> SHOULD not contain IP addresses/ports from whom the
> request has come. If it
> is so, I can't assume that the information is not
> used to assume from where
> (IP address/port) the request has come. Appreciate
> your response to clarify
> the point.
> 
>  
> 
>   As such, it is very important that the From URI
> not contain IP addresses
> or the FQDN
> 
>    of the host on which the UA is running, since
> these are not logical
> 
>    names.
> 
>  
> 
> Thank you,
> 
> Anil
> 
>  
> 
> This email contains material that is confidential.
> The content of this email
> is for the sole use of the intended recipient(s).
> Any review or distribution
> by persons other than the intended recipient(s)
> without the express
> permission of NetScreen Technologies, Inc. is
> strictly prohibited. If you
> are not the intended recipient, please contact the
> sender and delete/destroy
> all copies of this email and any related
> attachments. NetScreen does not
> guarantee the accuracy or completeness of third
> party materials or
> information.
> 
>  
> 
> 

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---

From: Jonathan Rosenberg <[email-masked]>
Date: Wed, 25 Feb 2004 15:20:00 -0500

Responses are sent to the Via address, though more commonly to the 
source IP/port of the request when TCP is used, or when rport is used 
(RFC 3581) with UDP. The IP/port in the Via effectively provide a 
fallback, to be used for the server to re-initiate a connection to the 
client in the event of failure to send the response.

Subsequent requests in a dialog are sent to the Contact URI.

 From is a logical identifier, used for display and policy purposes. 
Please, please don't muck with it.

Let me take this opportunity to preach a little on the role of ALGs in a 
network.

As a general rule, ALGs are quite problematic. They don't work in 
conjunction with most of the SIP security mechanisms, including S/MIME 
but more importantly sips and TLS. Their spotty presence in a network, 
generally undetectable to application entities in the network, cannot be 
depended on, and therefore can never serve as a complete solution for an 
application service provider. Worse yet, when (and I say when, not if) 
one of these ALGs does something wrong that breaks a call flow, it 
becomes almost impossible to diagnose and correct. Generally speaking, 
application layer intelligence does not belong in the core of the 
network; that brings us back to the days of single-service networks 
where the whole network needs to be upgraded to support a new 
application. ALGs are contrary to the hourglass model that is one of the 
defining characteristics of IP.

I much prefer solutions like ICE, STUN, TURN and MIDCOM, which separate 
application layer intelligence from firewalls and NATs, and allow for 
applications to do the right thing for themselves for the purposes of 
NAT traversal.

As such, the right model is to NOT build an ALG, but if you must, build 
a full protocol-compliant entity that just so happens to ship with and 
be co-resident in your firewall/nat. That entity must be directly 
addressed by other SIP entities, rather than being a transparent element 
in the network. It is only through this model that we can create robust 
and secure SIP networks.

-Jonathan R.

-- 
Jonathan D. Rosenberg, Ph.D.                600 Lanidex Plaza
Chief Technology Officer                    Parsippany, NJ 07054-2711
dynamicsoft
[email-masked]                     FAX:   (973) 952-5050
http://www.jdrosen.net                      PHONE: (973) 952-5000
http://www.dynamicsoft.com

---

From: "Ashir Ahmed" <[email-masked]>
Date: Fri, 27 Feb 2004 17:51:14 +0900

-Both To and From headers contain logical addresses. These headers are not
used for routing purposes.
-Contact header in general contains a SIP(S) URI for receiving subsequent
requests. However, this header is NOT used in PUBLISH and MESSAGE requests
as they do not expect any subsequent requests.

Please find a general guideline on these message headers and URI scheme
usage at
http://www.softfront.co.jp/tech/ietfdoc/draft/draft-ashir-simple-message-guideline-01.txt

Ashir

----- Original Message ----- 
From: "Jonathan Rosenberg" <[email-masked]>
To: "Anil Bollineni" <[email-masked]>
Cc: "'xiao'tong liang'" <[email-masked]>; <[email-masked]>;
<[email-masked]>
Sent: Thursday, February 26, 2004 5:20 AM
Subject: Re: [Sip] From Header