Subject: Re:[Sip] Record-Route, Path, Service Route, and Multi-Homed Proxies

From: feng zhang <[email-masked]>
Date: Fri, 25 Oct 2002 12:29:39 +0800

Hi Dean,

>This odd thing has two serious implications:
>
>1) UA2 cannot sign the route set, because it gets edited by P in the
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>response. Consequently, end-to-end protection of the route set can not
~~~~~~~~~~ I can not understand this point. If UA2 writes Route:192.168.2.1 in
           BYE to UA1, the P will not change the Route header, the P only
           strip this Route header in BYE, and passes it to UA1, NO route
           set is changed. I dont know why UA2 cannot sign the route set?
           u say P will edit the route set in response, and can u give me 
           an example? As I think , UA1 send 200 OK to UA2's BYE , the message
           200 OK has no Route header, what can P edit this response ?
           I am really confused. Thanks u very much!

>be supported by the protocol. We've just broken the openness principle
>and the end-to-end principle. Oops.
>
>2) P must implement special "multihomed" logic. On the request phase, it
>goes through output interface calculation and writes the output
>interface into the route. It must then inspect all responses, grep for
>an input interface, and selectively edit them to reference the correct
>output interface. This is a CPU drag. 
>

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---

From: Dean Willis <[email-masked]>
Date: 29 Oct 2002 13:59:29 -0600

> >1) UA2 cannot sign the route set, because it gets edited by P in the

Assume

UA1------P------UA2

where P is multi-homed. That is, it has an interface with one address
facing UA1, and a different interface with a different interface facing
UA2. There is NO IP level routability between UA1 and UA2.

Assume that the interface facing UA1 is 192.168.2.2 and the interface
facing UA2 is 63.64.250.82 (my house, oddly enough, has this setup)

So, UA1 sends an INVITE to P.
P adds a Record-Route <sip:63.64.250.82;lr> and sends the request on to
UA2. 

UA2 responds with a 200 OK reflecting the Record-Route back.

If P conforms to RFC3261, it must REWRITE the Record-Route header in the
200 Ok to have a value of <sip:192.168.2.2;lr> before passing the 200 OK
back to UA1.

Now, assume that UA2 had "signed" the Record-Route header, attaching it
in a body.

UA1 retrieves the signed body and compares the signed Record-Route with
the Record-Route in the 200 OK header. They don't match. What does this
mean?

--
Dean