$ sudo ggsn --gtp-linux -c ggsn.conf -f -d listen: (null) conf: ggsn.conf fg: 1 debug: 1 qos: 0x0b921f apn: internet net: 192.168.0.0/24 pidfile: /var/run/ggsn.pid statedir: /var/lib/ggsn/ gtp_linux: 1 timelimit: 0 cmdline_parser_configfile listen: 127.0.0.1 conf: ggsn.conf fg: 1 debug: 1 qos: 0x0b921f apn: internet net: 192.168.0.0/24 pidfile: /var/run/ggsn.pid statedir: /var/lib/ggsn/ gtp-linux: 1 timelimit: 0 <000c> gtp.c:701 GTP: gtp_newgsn() started <0002> gtp-kernel.c:123 Using the GTP kernel mode (genl ID is 27) <0002> gtp-kernel.c:156 GTP kernel configured <000b> control_if.c:693 CTRL at 127.0.0.1 4257 version 1 teid 1 address (6) f1 21 c0 a8 0 2 sgsn-addr (4) 7f 0 0 2 <000c> gtp.c:2581 Packet from 127.0.0.2:2152, length: 12 content: 32 1a 00 04 00 00 00 00 00 00 00 00 : Unknown PDP context <000c> gtp.c:2581 Packet from 127.0.0.2:2152, length: 12 content: 32 1a 00 04 00 00 00 00 00 00 00 00 : Unknown PDP context <000c> gtp.c:2581 Packet from 127.0.0.2:2152, length: 12 content: 32 1a 00 04 00 00 00 00 00 00 00 00 : Unknown PDP context version 1 teid 1 address (6) f1 21 c0 a8 0 2 sgsn-addr (4) 7f 0 0 2