NAT traversal with TCP is only possible, if you configure port forwarding at the NAT boxes, and configure your endpoints to use the configured ports and the public IP in the contact header.

Maybe another solution would be to establish the TCP session always from the endpoint to the SIP proxy. The problem is, as soon as the sip proxy finishes the TCP session, the endpoint has to re-connect again, to be able to receive SIP messages. This also depends on the way ser re-uses existing sessions.

regards klaus

Martin Rusnak wrote:

Hello

I have following use case:

Endpoint1 <------> NAT <------> SER <------> NAT <------> Endpoint2 10.0.0.10 TCP TCP 192.168.0.4

Both enpoints are behind a NAT, connected via TCP transport to SER. The problem is that no message can be routed between them. It looks like SER connot find open tcp connection. Here are the error messages copied from the log:

11(13977) build_req_from_req: id added: <;i=e71>, rcv proto=2 11(13977) parse_headers: flags=2048 11(13977) parse_headers: flags=2048 11(13977) parse_headers: flags=-1 11(13977) clen_builder: content-length: 281 (281) 11(13977) check_via_address(63.64.165.70, 10.0.0.10, 0) 11(13977) tcp_send: no open tcp connection found, opening new one 11(13977) ERROR: tcp_blocking_connect: SO_ERROR (113) No route to host 11(13977) ERROR: tcpconn_connect: tcp_blocking_connect failed 11(13977) ERROR: tcp_send: connect failed 11(13977) msg_send: ERROR: tcp_send failed 11(13977) ERROR: t_forward_nonack: sending request failed

The records for TCP subscribers behind a NAT contains local address like: Contact: 'sip:10.0.0.10:12451;transport=tcp' even if the function fix_contact() is called in registration.

So, how to configure SER for serving the TCP endpoints behind a NAT?

Martin

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