Question about libgtpnl

morteza ali Ahmadi morteza.ali.ahmadi at
Sun Jan 31 19:55:25 UTC 2021

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 and our SGSN IP is 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

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

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

(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
*When there is much light, The shadow is deep...*
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