[asterisk-users] Asterisk as a client: can I get the remote SIP server to ignore rport?

[Rusty Newton]

On Wed, Feb 19, 2014 at 11:53 AM, Markus <universe at truemetal.org> wrote:
> Hi list,
>
> I have a fresh install of Asterisk 12.0.0 and I'm going to use it only as a
> client. I'm trying to SIP REGISTER with a remote SIP provider.
>
> The situation is that Asterisk is running in a VMware VM with a RFC IP
> address (192.168.1.2). The provider of the VM performs static NAT from the
> RFC IP address to a dedicated public IP address, however, they are rewriting
> ports at will. That's the problem.
>
> Here's an excerpt from tcpdump:
<snip>
>
> I'm thinking the answer is "no", but is there any option how I can get the
> remote SIP provider to answer me on port 5060? Without having them to change
> anything in their config.

http://www.ietf.org/rfc/rfc3581.txt

To force RFC3581 support for outbound REGISTER messages, you can set
"nat=force_rport" in the general section of your sip.conf. (This also
forces RFC3581 compliance for inbound messages, for any peers that
inherit this general option)

In my testing this results in the outbound REGISTER setting rport like

"Via: SIP/2.0/UDP X.X.X.X:5060;branch=z9hG4bK493d3405;rport"

If the far end supports RFC3581 it should respond back to the port
from what it received requests. That should be 5060 if they receive
the message from 5060. However.. if your VM/Network provider is
rewriting things, then they could potentially remove your rport value,
send it out over a different port, or do any number of crazy things.
Depending on what they have going on in their network, receiving it
back at 5060 is no guarantee it'll get back to your Asterisk VM.

-- 
Rusty Newton
Digium, Inc. | Community Support Manager
445 Jan Davis Drive NW - Huntsville, AL 35806 - US
direct: +1 256 428 6200

Check us out at: http://digium.com & http://asterisk.org