> Such a return routability check is probably the best SIP can do in the
> presence of SBCs and the inability to get
> draft-fischer-sip-e2e-sec-media-01.txt or draft-wing-sip-identity-media-03.txt
> off the ground.
> 
> -d

I believe this sums it up; correct and balanced.

Henry


On 10/28/08 10:52 PM, "Dan Wing" <[EMAIL PROTECTED]> wrote:

>> With SIP, you don't know that the originating UAS has the same name as
>> it is claiming to have, because you got the SIP message from some
>> nearby proxy.  DERIVE is more like doing a reverse DNS lookup to see
>> if the originating host has the name that it claims to have.
> 
> Yeah, that's walking the DNS tree.  It is valuable; heck, IETF's own
> mailservers are doing it to reduce spam so it Must Be Good!  :-)
> 
> DERIVE is checking to see if your SIP routing takes you to the
> same place that (claims to) be originating the incoming INVITE.
> It is using your *outgoing* SIP routing -- which you must already
> trust to send outbound messages -- to test the validity of the
> (proported) From: address of an incoming INVITE.
> 
> 
> Such a return routability check is probably the best SIP can do in the
> presence of SBCs and the inability to get
> draft-fischer-sip-e2e-sec-media-01.txt or draft-wing-sip-identity-media-03.txt
> off the ground.
> 
> -d
> 
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