Hi, osmocom team members

We have run OsmoGGSN project using the attached config file in this email and the following command:

osmo-ggsn

As you can see in the config file, we have set IP 127.0.0.2 for GGSN. After executing the above command, a tunnel named tun4 is created.

To communicate with SGSN, we use the SGSN emulator in OsmoGGSN as follow:

sgsnemu -l 127.0.0.1 -r 127.0.0.2

After executing the above command, we see that 2 packets are sent from SGSN to GGSN. These packets are "Echo request" and "Create PDP context request" and GGSN responses to SGSN with the packets "Echo response" and "Create PDP context response".

To test tun4, we send a GTP <DNS> packet containing an arbitrary query to GGSN and we see that this GTP <DNS> packet is received in Loopback (lo) interface and also, the DNS packet is received in tun4 interface. But there is no DNS response to our query neither in tun4 interface nor lo interface. A screenshot of the lo interface and tun4 interface in the wireshark is attached in this email (right is lo and left is tun4).

How can we receive DNS responses to our DNS query? (Does tun4 require routing or something else?)