[Asterisk-Users] SIP + NAT = horrible mess

[Leo Ann Boon]

Kim Lux wrote:

>I was expecting to have to port forward too and yet our setup doesn't
>require it, not on the laptop nor on the wireless router. 
>
>I think as long as the SIP clients open a port on the NATing device and
>keep them open so the SIP provider can connect to it, all is well, even
>if STUN isn't used.  
>
>I was surprised by how easy it was to NAT the Grandstreams.  I had
>visions of having every device being assigned a static IP and having a
>fistful of port forwards assigned to them on the router.   
>  
>
You're connecting to a SIP provider or just Asterisk? Most SIP provider 
use a far-end NAT traversal device like Jasomi, Acmepacket or Kagoo. The 
NAT traversal device has the intelligence to figure out the UDP port 
mapping used by the NAT. SER + nathelper has the effect. For my SER 
setup, most of the time we can just plug the SIP phone into a router and 
it will work without any special config. Unfortunately, there're certain 
firewalls like PIX and MS ISA that will fail. In those cases, your best 
bet is to do port forwarding or use an outbound proxy. IIRC, Vonage also 
has the same problem.