[asterisk-users] Asterisk 1.8.7.2 now sends rport always

[Kevin P. Fleming]

On 12/18/2011 01:22 PM, José Pablo Méndez Soto wrote:

> Embarrassingly enough,  I just tried the nat=no again both in the
> general and peer sections and the blessed phone registered.... My
> apologies, again, I wrote the thread late at night probably this blinded me.

No problem, we've all done that :-)

> Now, one question about a previous answer from you ("It is exactly that;
> 'force_rport' is now the default....."):
>
> is the trigger for using the source UDP port from the REGISTER, inside
> the rport field and inside the destination UDP port of the 200 OK:
>
>  1. The mismatch between the UDP source port of the REGISTER and the VIA
>     port?   Or
>  2. The fact that the other entity sends an empty rport?
>  3. Or any of the above?
>
> Its a difficult question to ask/describe, so if I am not asking
> correctly please let me know. Thanks a lot, really.

Not at all. The trigger for Asterisk to respond to the port that the 
request was sent from, instead of the port listed in the top-most Via 
header, is *exactly* 'force_rport'. This causes Asterisk to behave as if 
the 'rport' parameter was included in the top-most Via header, which 
would be an explicit request from the sending UA for Asterisk to respond 
to the sending port (and also report back what the sending port was, but 
that's not part of the problem here).

So, if the sending UA include an empty 'rport' parameter in its top-most 
Via header, *or* if the Asterisk has been told to act as if one had been 
included even if it wasn't, then Asterisk will respond to the perceived 
sending port; otherwise, it will respond to the port listed in the 
top-most Via header.

As far as we know from our research before making this change, the Cisco 
phones in question are the only ones that send their requests from one 
port and require the responses to go back to a different port. All other 
phones that we (and others) use with Asterisk use the same port for 
both, which makes them quite easy to use behind NAT devices. The Cisco 
phone models you are dealing with won't work behind a NAT device unless 
that NAT device has a 'helper' that understands SIP and can fix up this 
situation (and of course many Cisco phone users have Cisco routers that 
do exactly this).

-- 
Kevin P. Fleming
Digium, Inc. | Director of Software Technologies
Jabber: kfleming at digium.com | SIP: kpfleming at digium.com | Skype: kpfleming
445 Jan Davis Drive NW - Huntsville, AL 35806 - USA
Check us out at www.digium.com & www.asterisk.org