Hi Osmocom team
We have a basic question about libgtpnl (Linux Kernel GTP-U).

We receive a lot of GTP <DNS> packets which are sent from MS to our HNB and from HNB to our SGSN (a screenshot is attached in this email). As you can see in the one of these packets in the attached image, our MS IP is 10.250.0.114 and our SGSN IP is 172.60.3.154. Also, our TEID is 100 which is set in RAB-Assignment Request sending from SGSN to HNB. In order to put these GTP packets in our GTP tunnel, we use libgtpnl and the two following commands:

gtp-link add gtp1
gtp-tunnel add gtp1 v1 100 1 10.250.0.114 172.60.3.154

But when we monitor the gtp1 interface in the wireshark, there is no packet on this interface. Could you please help us to know the reason for this problem?

(It is worth mentioning that after receiving these GTP <DNS> packets from MS to SGSN and using netstat, we see that Recv-Q (bytes in UDP port 2152 which are ready to read) is increased to a value more than 0)

Best regards

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