Documentation/networking/gtp.rst

1 .. SPDX-License-Identifier: GPL-2.0
11 In 'drivers/net/gtp.c' you are finding a kernel-level implementation
18 tunneling User-IP payload between a mobile station (phone, modem)
29 technology-dependent protocol stack for transmitting the user IP
35 is translated into GTP *without breaking the end-to-end tunnel*.  So
38 At some point the GTP packet ends up on the so-called GGSN (GSM/UMTS)
39 or P-GW (LTE), which terminates the tunnel, decapsulates the packet
42 theoretically some non-IP network like X.25).
58 It *only* implements the so-called 'user plane', carrying the User-IP
59 payload, called GTP-U.  It does not implement the 'control plane',
61 GTP tunnels (GTP-C).
63 So in order to have a working GGSN/P-GW setup, you will need a
64 userspace program that implements the GTP-C protocol and which then
65 uses the netlink interface provided by the GTP-U module in the kernel
78 https://osmocom.org/projects/linux-kernel-gtp-u/wiki
80 Userspace Programs with Linux Kernel GTP-U support
84 implementations that implement GTP-C and can use the netlink interface
85 to make use of the Linux kernel GTP-U support:
90 * ergw (GGSN + P-GW in Erlang):
97 libmnl and which implements a C-language API towards the netlink
105 There are two different versions of GTP-U: v0 [GSM TS 09.60] and v1
110 GTP-U uses UDP for transporting PDUs.  The receiving UDP port is 2151
111 for GTPv1-U and 3386 for GTPv0-U.
113 There are three versions of GTP-C: v0, v1, and v2.  As the kernel
114 doesn't implement GTP-C, we don't have to worry about this.  It's the
133 osmocom-net-grps mailing list for related discussion. The list can be
134 reached at osmocom-net-gprs@lists.osmocom.org and the mailman
136 https://lists.osmocom.org/mailman/listinfo/osmocom-net-gprs
141 The Osmocom project maintains an issue tracker for the Kernel GTP-U
143 https://osmocom.org/projects/linux-kernel-gtp-u/issues
159 Local GTP-U entity and tunnel identification
160 --------------------------------------------
162 GTP-U uses UDP for transporting PDU's. The receiving UDP port is 2152
163 for GTPv1-U and 3386 for GTPv0-U.
165 There is only one GTP-U entity (and therefore SGSN/GGSN/S-GW/PDN-GW
167 per GTP-U entity.
185   The TEID in the GTP-U header is used to de-multiplex traffic
189   Therefore no two remote GTP-U endpoints shall send traffic to a
190   GTP-U protocol entity using the same TEID value except
193 The definition above only defines that two remote GTP-U endpoints
196 necessary that the GTP-U entity accepts traffic for TEIDs from
205 The GTP-U driver creates a Linux network device for each Gi/SGi
209 may lead to the impression that the GGSN/P-GW can have only one such
213 between +the 3GPP packet domain (PDN) based on GTP-U tunnel and IP
217 number of Gi/SGi interfaces implemented by a GGSN/P-GW.
224      will result in different private networks having overlapping
226      tunnel or layer 2 virtual circuit) is used between the GGSN/P-GW
233 In order to support the overlapping address range use case, each APN
238    The Access Point Name is purely a control plane (GTP-C) concept.
239    At the GTP-U level, only Tunnel Endpoint Identifiers are present in
240    GTP-U packets and network devices are known
244   * network device + MS IP -> Peer IP + Peer TEID,
248   * local GTP-U IP + TEID  -> network device
250 Furthermore, before a received T-PDU is injected into the network