Cellular Network Infrastructure » Core Network (CN) » OsmoSGSN

The bug seems to be triggered when the Iu-Release is performed, the GTP-U endpoints are updated (with Update PDP Context Request), and when the GTP-U packet arrives from GGSN to SGSN, then PDP context for given TEID is not found and then it is hard-dropped because of the error in gtp.c:

May 07 15:16:17 Core osmo-sgsn[4054]: <0023> gtp.c:2378 Packet from 10.0.1.123:2123, length: 55 content: 32 13 00 2f 00 00 00 01 98 1d 00 00 01 80 10 00 00 00 01 7f 0b 56 70 83 85 00 04 0a 00 01 7b 85 00 04 c0 a8 0e 10 87 00 0e 00 00 00 00 00 00 00 00 00 00 00 00 00 00 : Missing information field
May 07 15:16:17 Core osmo-sgsn[4054]: <000e> sgsn_libgtp.c:644 libgtp cb_conf(type=18, cause=-1, pdp=0x7f6447263060, cbp=0xc0eae0)
May 07 15:16:17 Core osmo-sgsn[4054]: <000e> sgsn_libgtp.c:648 libgtp EOF (type=18, pdp=0x7f6447263060, cbp=0xc0eae0)
May 07 15:16:17 Core osmo-sgsn[4054]: <0023> gtp.c:2800 Packet from 192.168.14.16:2152, length: 60 content: 30 ff 00 34 00 00 00 09 45 00 00 34 0a 29 00 00 f4 06 dc 57 45 ad 90 95 0a 00 00 01 01 bb ce 32 f1 00 89 77 34 68 f8 fa 80 11 0e 24 24 bd 00 00 01 01 08 0a c3 05 ef 21 00 05 39 a2 : Unknown PDP context, GTPv1
May 07 15:16:17 Core osmo-sgsn[4054]: <000e> sgsn_libgtp.c:669 PDP(248010132392306:5): Context 0x7f6447263060 was deleted
May 07 15:16:17 Core osmo-sgsn[4054]: <000e> gprs_sgsn.c:740 PDP(248010132392306/0) Hard-dropping PDP ctx due to GGSN recovery
May 07 15:16:17 Core osmo-sgsn[4054]: <0023> pdp.c:255 Begin pdp_tiddel tid = 5603293231010842
May 07 15:16:17 Core osmo-sgsn[4054]: <0023> pdp.c:262 End pdp_tiddel: PDP found

The relevant PCAP and logs are attached.
10.0.2.52 - Femtocell
10.0.2.51 - SGSN
10.0.1.123 or 192.168.14.16 - GGSN

I use a filthy hack which is to comment out the call to mmctx_change_gtpu_endpoints_to_sgsn function in sgsn.

Btw, possibly bug in the gtp library...