[Asterisk-Users] 2 Sip phones behind un-natted Asterisk

[John Fraizer]

Barry Fawthrop wrote:

>>The problem is probably that both of your SIP phones are using the same 
>>port.  I played with two 7960's behind a Linksys on Saturday and finally 
>>got them playing right when I changed the following:
>>
>>In Phone 1's SIP[macaddr].cnf:
>>
>>voip_control_port: 5061
>>
>>In Phone 2's SIP[macaddr].cnf:
>>
>>voip_control_port: 5062
>>
>>The default control port is 5060.  Note:  This is the port that the 
>>PHONE uses to initiate the connection to * and not the port it is 
>>connecting to.
>>
> 
> 
> I'm having a similar problem with snom 200s would changing the port
> work there also or is that just a 7960 issue?  Do you or any other
> know where I would  change that on a snom 200 ??
> 
> thanks in advance
> 
> Barry


It's not phone specific.  It's part the way your nat is working.  It 
tracks things based on flows and a flow is sourceIP:sourcePort <-> 
destIP:destPort.

When you have two devices inside your NAT sourcing from the same port 
and going to the same destIP:port, it doesn't know what to do with 
packets returning from the destIP:port because it has more than one flow 
that matches.

So, if you have multiple devices (hard or soft phones) on the inside 
that are trying to register on the same sip proxy or * server, you need 
to make sure that they use unique source ports.

John