[Blink] Blink over VPN using the wrong ip address in headers

Saúl Ibarra Corretgé saul at ag-projects.com
Thu May 12 09:53:31 CEST 2011

>> Having the wrong IP address in the Via header is a known issue but it
>> shouldn't matter since rport (RFC 3581) is requested and should be used.
> I'm not familiar with RFC 3581 (yet), but did you mean, "should be used"
> by the SIP server? Or client?

Client requests its use by adding 'rport' to the Via header, and server 
should honor that.

>> When using UDP, if rport is not used responses are routed back to the source
>> address and the port in the topmost Via header. Since this may cause trouble
>> with NATs, if rport is being used, responses will be routed to the source IP
>> and port from which the request originated.
> So, if I parse this correctly, the SIP server needs to do some magic?
> Blink is sending this wrong address in the first packet, so the SIP server
> should ignore it and send replies to the "Contact" address anyway?

Not to the Contact, to the IP address and port where he (the server) 
received the request.

>> What SIP server are you using?
>  From what I can tell from tcpdump[0] it's an Asterisk PBX.

In the trace I see that responses to SUBSCRIBE requests are routed 
correctly (see the 403) so looks like Asterisk is not acting in the same 
way for REGISTERs and for SUBSCRIBEs.

If you are in control of the server, what is the 'nat' setting for the 
peer '356'?


Saúl Ibarra Corretgé
AG Projects

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