Commit 81baecb6 authored by Mauro Carvalho Chehab's avatar Mauro Carvalho Chehab Committed by David S. Miller

docs: networking: convert gtp.txt to ReST

- add SPDX header;
- adjust titles and chapters, adding proper markups;
- add notes markups;
- adjust identation, whitespaces and blank lines;
- add to networking/index.rst.
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 8c498935
.. SPDX-License-Identifier: GPL-2.0
=====================================
The Linux kernel GTP tunneling module The Linux kernel GTP tunneling module
====================================================================== =====================================
Documentation by Harald Welte <laforge@gnumonks.org> and
Documentation by
Harald Welte <laforge@gnumonks.org> and
Andreas Schultz <aschultz@tpip.net> Andreas Schultz <aschultz@tpip.net>
In 'drivers/net/gtp.c' you are finding a kernel-level implementation In 'drivers/net/gtp.c' you are finding a kernel-level implementation
of a GTP tunnel endpoint. of a GTP tunnel endpoint.
== What is GTP == What is GTP
===========
GTP is the Generic Tunnel Protocol, which is a 3GPP protocol used for GTP is the Generic Tunnel Protocol, which is a 3GPP protocol used for
tunneling User-IP payload between a mobile station (phone, modem) tunneling User-IP payload between a mobile station (phone, modem)
...@@ -41,7 +47,8 @@ publicly via the 3GPP website at http://www.3gpp.org/DynaReport/29060.htm ...@@ -41,7 +47,8 @@ publicly via the 3GPP website at http://www.3gpp.org/DynaReport/29060.htm
A direct PDF link to v13.6.0 is provided for convenience below: A direct PDF link to v13.6.0 is provided for convenience below:
http://www.etsi.org/deliver/etsi_ts/129000_129099/129060/13.06.00_60/ts_129060v130600p.pdf http://www.etsi.org/deliver/etsi_ts/129000_129099/129060/13.06.00_60/ts_129060v130600p.pdf
== The Linux GTP tunnelling module == The Linux GTP tunnelling module
===============================
The module implements the function of a tunnel endpoint, i.e. it is The module implements the function of a tunnel endpoint, i.e. it is
able to decapsulate tunneled IP packets in the uplink originated by able to decapsulate tunneled IP packets in the uplink originated by
...@@ -70,7 +77,8 @@ Userspace :) ...@@ -70,7 +77,8 @@ Userspace :)
The official homepage of the module is at The official homepage of the module is at
https://osmocom.org/projects/linux-kernel-gtp-u/wiki https://osmocom.org/projects/linux-kernel-gtp-u/wiki
== Userspace Programs with Linux Kernel GTP-U support == Userspace Programs with Linux Kernel GTP-U support
==================================================
At the time of this writing, there are at least two Free Software At the time of this writing, there are at least two Free Software
implementations that implement GTP-C and can use the netlink interface implementations that implement GTP-C and can use the netlink interface
...@@ -82,7 +90,8 @@ to make use of the Linux kernel GTP-U support: ...@@ -82,7 +90,8 @@ to make use of the Linux kernel GTP-U support:
* ergw (GGSN + P-GW in Erlang): * ergw (GGSN + P-GW in Erlang):
https://github.com/travelping/ergw https://github.com/travelping/ergw
== Userspace Library / Command Line Utilities == Userspace Library / Command Line Utilities
==========================================
There is a userspace library called 'libgtpnl' which is based on There is a userspace library called 'libgtpnl' which is based on
libmnl and which implements a C-language API towards the netlink libmnl and which implements a C-language API towards the netlink
...@@ -90,7 +99,8 @@ interface provided by the Kernel GTP module: ...@@ -90,7 +99,8 @@ interface provided by the Kernel GTP module:
http://git.osmocom.org/libgtpnl/ http://git.osmocom.org/libgtpnl/
== Protocol Versions == Protocol Versions
=================
There are two different versions of GTP-U: v0 [GSM TS 09.60] and v1 There are two different versions of GTP-U: v0 [GSM TS 09.60] and v1
[3GPP TS 29.281]. Both are implemented in the Kernel GTP module. [3GPP TS 29.281]. Both are implemented in the Kernel GTP module.
...@@ -105,7 +115,8 @@ doesn't implement GTP-C, we don't have to worry about this. It's the ...@@ -105,7 +115,8 @@ doesn't implement GTP-C, we don't have to worry about this. It's the
responsibility of the control plane implementation in userspace to responsibility of the control plane implementation in userspace to
implement that. implement that.
== IPv6 == IPv6
====
The 3GPP specifications indicate either IPv4 or IPv6 can be used both The 3GPP specifications indicate either IPv4 or IPv6 can be used both
on the inner (user) IP layer, or on the outer (transport) layer. on the inner (user) IP layer, or on the outer (transport) layer.
...@@ -114,22 +125,25 @@ Unfortunately, the Kernel module currently supports IPv6 neither for ...@@ -114,22 +125,25 @@ Unfortunately, the Kernel module currently supports IPv6 neither for
the User IP payload, nor for the outer IP layer. Patches or other the User IP payload, nor for the outer IP layer. Patches or other
Contributions to fix this are most welcome! Contributions to fix this are most welcome!
== Mailing List == Mailing List
============
If yo have questions regarding how to use the Kernel GTP module from If you have questions regarding how to use the Kernel GTP module from
your own software, or want to contribute to the code, please use the your own software, or want to contribute to the code, please use the
osmocom-net-grps mailing list for related discussion. The list can be osmocom-net-grps mailing list for related discussion. The list can be
reached at osmocom-net-gprs@lists.osmocom.org and the mailman reached at osmocom-net-gprs@lists.osmocom.org and the mailman
interface for managing your subscription is at interface for managing your subscription is at
https://lists.osmocom.org/mailman/listinfo/osmocom-net-gprs https://lists.osmocom.org/mailman/listinfo/osmocom-net-gprs
== Issue Tracker == Issue Tracker
=============
The Osmocom project maintains an issue tracker for the Kernel GTP-U The Osmocom project maintains an issue tracker for the Kernel GTP-U
module at module at
https://osmocom.org/projects/linux-kernel-gtp-u/issues https://osmocom.org/projects/linux-kernel-gtp-u/issues
== History / Acknowledgements == History / Acknowledgements
==========================
The Module was originally created in 2012 by Harald Welte, but never The Module was originally created in 2012 by Harald Welte, but never
completed. Pablo came in to finish the mess Harald left behind. But completed. Pablo came in to finish the mess Harald left behind. But
...@@ -139,9 +153,11 @@ In 2015, Andreas Schultz came to the rescue and fixed lots more bugs, ...@@ -139,9 +153,11 @@ In 2015, Andreas Schultz came to the rescue and fixed lots more bugs,
extended it with new features and finally pushed all of us to get it extended it with new features and finally pushed all of us to get it
mainline, where it was merged in 4.7.0. mainline, where it was merged in 4.7.0.
== Architectural Details == Architectural Details
=====================
=== Local GTP-U entity and tunnel identification === Local GTP-U entity and tunnel identification
--------------------------------------------
GTP-U uses UDP for transporting PDU's. The receiving UDP port is 2152 GTP-U uses UDP for transporting PDU's. The receiving UDP port is 2152
for GTPv1-U and 3386 for GTPv0-U. for GTPv1-U and 3386 for GTPv0-U.
...@@ -164,15 +180,15 @@ Therefore: ...@@ -164,15 +180,15 @@ Therefore:
destination IP and the tunnel endpoint id. The source IP and port destination IP and the tunnel endpoint id. The source IP and port
have no meaning and can change at any time. have no meaning and can change at any time.
[3GPP TS 29.281] Section 4.3.0 defines this so: [3GPP TS 29.281] Section 4.3.0 defines this so::
> The TEID in the GTP-U header is used to de-multiplex traffic The TEID in the GTP-U header is used to de-multiplex traffic
> incoming from remote tunnel endpoints so that it is delivered to the incoming from remote tunnel endpoints so that it is delivered to the
> User plane entities in a way that allows multiplexing of different User plane entities in a way that allows multiplexing of different
> users, different packet protocols and different QoS levels. users, different packet protocols and different QoS levels.
> Therefore no two remote GTP-U endpoints shall send traffic to a Therefore no two remote GTP-U endpoints shall send traffic to a
> GTP-U protocol entity using the same TEID value except GTP-U protocol entity using the same TEID value except
> for data forwarding as part of mobility procedures. for data forwarding as part of mobility procedures.
The definition above only defines that two remote GTP-U endpoints The definition above only defines that two remote GTP-U endpoints
*should not* send to the same TEID, it *does not* forbid or exclude *should not* send to the same TEID, it *does not* forbid or exclude
...@@ -183,7 +199,8 @@ multiple or unknown peers. ...@@ -183,7 +199,8 @@ multiple or unknown peers.
Therefore, the receiving side identifies tunnels exclusively based on Therefore, the receiving side identifies tunnels exclusively based on
TEIDs, not based on the source IP! TEIDs, not based on the source IP!
== APN vs. Network Device == APN vs. Network Device
======================
The GTP-U driver creates a Linux network device for each Gi/SGi The GTP-U driver creates a Linux network device for each Gi/SGi
interface. interface.
...@@ -201,29 +218,33 @@ number of Gi/SGi interfaces implemented by a GGSN/P-GW. ...@@ -201,29 +218,33 @@ number of Gi/SGi interfaces implemented by a GGSN/P-GW.
[3GPP TS 29.061] Section 11.3 makes it clear that the selection of a [3GPP TS 29.061] Section 11.3 makes it clear that the selection of a
specific Gi/SGi interfaces is made through the Access Point Name specific Gi/SGi interfaces is made through the Access Point Name
(APN): (APN)::
> 2. each private network manages its own addressing. In general this 2. each private network manages its own addressing. In general this
> will result in different private networks having overlapping will result in different private networks having overlapping
> address ranges. A logically separate connection (e.g. an IP in IP address ranges. A logically separate connection (e.g. an IP in IP
> tunnel or layer 2 virtual circuit) is used between the GGSN/P-GW tunnel or layer 2 virtual circuit) is used between the GGSN/P-GW
> and each private network. and each private network.
>
> In this case the IP address alone is not necessarily unique. The In this case the IP address alone is not necessarily unique. The
> pair of values, Access Point Name (APN) and IPv4 address and/or pair of values, Access Point Name (APN) and IPv4 address and/or
> IPv6 prefixes, is unique. IPv6 prefixes, is unique.
In order to support the overlapping address range use case, each APN In order to support the overlapping address range use case, each APN
is mapped to a separate Gi/SGi interface (network device). is mapped to a separate Gi/SGi interface (network device).
NOTE: The Access Point Name is purely a control plane (GTP-C) concept. .. note::
At the GTP-U level, only Tunnel Endpoint Identifiers are present in
GTP-U packets and network devices are known The Access Point Name is purely a control plane (GTP-C) concept.
At the GTP-U level, only Tunnel Endpoint Identifiers are present in
GTP-U packets and network devices are known
Therefore for a given UE the mapping in IP to PDN network is: Therefore for a given UE the mapping in IP to PDN network is:
* network device + MS IP -> Peer IP + Peer TEID, * network device + MS IP -> Peer IP + Peer TEID,
and from PDN to IP network: and from PDN to IP network:
* local GTP-U IP + TEID -> network device * local GTP-U IP + TEID -> network device
Furthermore, before a received T-PDU is injected into the network Furthermore, before a received T-PDU is injected into the network
......
...@@ -62,6 +62,7 @@ Contents: ...@@ -62,6 +62,7 @@ Contents:
generic-hdlc generic-hdlc
generic_netlink generic_netlink
gen_stats gen_stats
gtp
.. only:: subproject and html .. only:: subproject and html
......
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