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diff --git a/Documentation/networking/gtp.txt b/Documentation/networking/gtp.txt deleted file mode 100644 index 6966bbec1ecb..000000000000 --- a/Documentation/networking/gtp.txt +++ /dev/null @@ -1,230 +0,0 @@ -The Linux kernel GTP tunneling module -====================================================================== -Documentation by Harald Welte <laforge@gnumonks.org> and - Andreas Schultz <aschultz@tpip.net> - -In 'drivers/net/gtp.c' you are finding a kernel-level implementation -of a GTP tunnel endpoint. - -== What is GTP == - -GTP is the Generic Tunnel Protocol, which is a 3GPP protocol used for -tunneling User-IP payload between a mobile station (phone, modem) -and the interconnection between an external packet data network (such -as the internet). - -So when you start a 'data connection' from your mobile phone, the -phone will use the control plane to signal for the establishment of -such a tunnel between that external data network and the phone. The -tunnel endpoints thus reside on the phone and in the gateway. All -intermediate nodes just transport the encapsulated packet. - -The phone itself does not implement GTP but uses some other -technology-dependent protocol stack for transmitting the user IP -payload, such as LLC/SNDCP/RLC/MAC. - -At some network element inside the cellular operator infrastructure -(SGSN in case of GPRS/EGPRS or classic UMTS, hNodeB in case of a 3G -femtocell, eNodeB in case of 4G/LTE), the cellular protocol stacking -is translated into GTP *without breaking the end-to-end tunnel*. So -intermediate nodes just perform some specific relay function. - -At some point the GTP packet ends up on the so-called GGSN (GSM/UMTS) -or P-GW (LTE), which terminates the tunnel, decapsulates the packet -and forwards it onto an external packet data network. This can be -public internet, but can also be any private IP network (or even -theoretically some non-IP network like X.25). - -You can find the protocol specification in 3GPP TS 29.060, available -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: -http://www.etsi.org/deliver/etsi_ts/129000_129099/129060/13.06.00_60/ts_129060v130600p.pdf - -== The Linux GTP tunnelling module == - -The module implements the function of a tunnel endpoint, i.e. it is -able to decapsulate tunneled IP packets in the uplink originated by -the phone, and encapsulate raw IP packets received from the external -packet network in downlink towards the phone. - -It *only* implements the so-called 'user plane', carrying the User-IP -payload, called GTP-U. It does not implement the 'control plane', -which is a signaling protocol used for establishment and teardown of -GTP tunnels (GTP-C). - -So in order to have a working GGSN/P-GW setup, you will need a -userspace program that implements the GTP-C protocol and which then -uses the netlink interface provided by the GTP-U module in the kernel -to configure the kernel module. - -This split architecture follows the tunneling modules of other -protocols, e.g. PPPoE or L2TP, where you also run a userspace daemon -to handle the tunnel establishment, authentication etc. and only the -data plane is accelerated inside the kernel. - -Don't be confused by terminology: The GTP User Plane goes through -kernel accelerated path, while the GTP Control Plane goes to -Userspace :) - -The official homepage of the module is at -https://osmocom.org/projects/linux-kernel-gtp-u/wiki - -== Userspace Programs with Linux Kernel GTP-U support == - -At the time of this writing, there are at least two Free Software -implementations that implement GTP-C and can use the netlink interface -to make use of the Linux kernel GTP-U support: - -* OpenGGSN (classic 2G/3G GGSN in C): - https://osmocom.org/projects/openggsn/wiki/OpenGGSN - -* ergw (GGSN + P-GW in Erlang): - https://github.com/travelping/ergw - -== Userspace Library / Command Line Utilities == - -There is a userspace library called 'libgtpnl' which is based on -libmnl and which implements a C-language API towards the netlink -interface provided by the Kernel GTP module: - -http://git.osmocom.org/libgtpnl/ - -== Protocol Versions == - -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. -Version 0 is a legacy version, and deprecated from recent 3GPP -specifications. - -GTP-U uses UDP for transporting PDUs. The receiving UDP port is 2151 -for GTPv1-U and 3386 for GTPv0-U. - -There are three versions of GTP-C: v0, v1, and v2. As the kernel -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 -implement that. - -== IPv6 == - -The 3GPP specifications indicate either IPv4 or IPv6 can be used both -on the inner (user) IP layer, or on the outer (transport) layer. - -Unfortunately, the Kernel module currently supports IPv6 neither for -the User IP payload, nor for the outer IP layer. Patches or other -Contributions to fix this are most welcome! - -== Mailing List == - -If yo have questions regarding how to use the Kernel GTP module from -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 -reached at osmocom-net-gprs@lists.osmocom.org and the mailman -interface for managing your subscription is at -https://lists.osmocom.org/mailman/listinfo/osmocom-net-gprs - -== Issue Tracker == - -The Osmocom project maintains an issue tracker for the Kernel GTP-U -module at -https://osmocom.org/projects/linux-kernel-gtp-u/issues - -== History / Acknowledgements == - -The Module was originally created in 2012 by Harald Welte, but never -completed. Pablo came in to finish the mess Harald left behind. But -doe to a lack of user interest, it never got merged. - -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 -mainline, where it was merged in 4.7.0. - -== Architectural Details == - -=== Local GTP-U entity and tunnel identification === - -GTP-U uses UDP for transporting PDU's. The receiving UDP port is 2152 -for GTPv1-U and 3386 for GTPv0-U. - -There is only one GTP-U entity (and therefor SGSN/GGSN/S-GW/PDN-GW -instance) per IP address. Tunnel Endpoint Identifier (TEID) are unique -per GTP-U entity. - -A specific tunnel is only defined by the destination entity. Since the -destination port is constant, only the destination IP and TEID define -a tunnel. The source IP and Port have no meaning for the tunnel. - -Therefore: - - * when sending, the remote entity is defined by the remote IP and - the tunnel endpoint id. The source IP and port have no meaning and - can be changed at any time. - - * when receiving the local entity is defined by the local - destination IP and the tunnel endpoint id. The source IP and port - have no meaning and can change at any time. - -[3GPP TS 29.281] Section 4.3.0 defines this so: - -> 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 -> User plane entities in a way that allows multiplexing of different -> users, different packet protocols and different QoS levels. -> Therefore no two remote GTP-U endpoints shall send traffic to a -> GTP-U protocol entity using the same TEID value except -> for data forwarding as part of mobility procedures. - -The definition above only defines that two remote GTP-U endpoints -*should not* send to the same TEID, it *does not* forbid or exclude -such a scenario. In fact, the mentioned mobility procedures make it -necessary that the GTP-U entity accepts traffic for TEIDs from -multiple or unknown peers. - -Therefore, the receiving side identifies tunnels exclusively based on -TEIDs, not based on the source IP! - -== APN vs. Network Device == - -The GTP-U driver creates a Linux network device for each Gi/SGi -interface. - -[3GPP TS 29.281] calls the Gi/SGi reference point an interface. This -may lead to the impression that the GGSN/P-GW can have only one such -interface. - -Correct is that the Gi/SGi reference point defines the interworking -between +the 3GPP packet domain (PDN) based on GTP-U tunnel and IP -based networks. - -There is no provision in any of the 3GPP documents that limits the -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 -specific Gi/SGi interfaces is made through the Access Point Name -(APN): - -> 2. each private network manages its own addressing. In general this -> will result in different private networks having overlapping -> 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 -> and each private network. -> -> In this case the IP address alone is not necessarily unique. The -> pair of values, Access Point Name (APN) and IPv4 address and/or -> IPv6 prefixes, is unique. - -In order to support the overlapping address range use case, each APN -is mapped to a separate Gi/SGi interface (network device). - -NOTE: 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: - * network device + MS IP -> Peer IP + Peer TEID, - -and from PDN to IP network: - * local GTP-U IP + TEID -> network device - -Furthermore, before a received T-PDU is injected into the network -device the MS IP is checked against the IP recorded in PDP context. |