Hi,

After successfully making libgtpnl works between 02 Linux Host, now I am in the step of connecting one Linux Host to a real live SGSN this morning.

I don't have any particular issue at GTP-C side:

 - the Mobile Station registered on 3G network, requests one activate PDP context to the SGSN
 - the SGSN sends to my ggsn a create PDP context
 - my ggsn accepts it, and answers with all the needed information, such as MS_Address, DNS Address 1, DNS address 2, IP of GGSN-C, IP of GGSN-U, TEID Control Plane, TEID user plane, .... everything should be OK.
 - upon receipt of my creade_pdp_context_response accepted, the SGSN now try to establish a Tunnel with the given TEID towards my GGSN
 - but I cannot see anything on my GTPU-side in ggsn, apart of several echo-request message from SGSN
 - Sure, SGSN try to test connectivity to my ggsn GTPU by using echo-request, but no response
 - I don't know maybe because of no response, or because of SGSN alert me with an error gtpu-sm-cause-update-ggsn-path-failure, the SGSN decide to send a delete request

So I have 02 questions please:

 - 1) At GTP-C, I can implement all messages(echo-response, create-response, delete-response) but at GTPU-side, as the port is used by libgtpnl, I cannot implement an echo-response at all ==> So, do libgtpnl is supposed to answer or not to an echo-response received from a SGSN at GTPU-level?

 - 2) When I tried a Linux-to-Linux setup, it worked because I specified the ms_addr and sgsn_addr in the 02 Linux Host.
 But as I cannot configure anything about the tunnel at SGSN-side(done automatically by SGSN), I can only create the tunnel at ggsn-side thanks to my user space program, by passing the TEID and ms_addr input to libgtpnl. Does it mean that libgtpnl only complies with OpenGGSN, ergw, and OpenAirInterface but not intended to ber used with a real SGSN?

Thanks for clarifying me,
Best Regards,