path: root/Documentation/networking
diff options
authorLinus Torvalds <torvalds@linux-foundation.org>2010-05-21 04:04:44 (GMT)
committerLinus Torvalds <torvalds@linux-foundation.org>2010-05-21 04:04:44 (GMT)
commitf8965467f366fd18f01feafb5db10512d7b4422c (patch)
tree3706a9cd779859271ca61b85c63a1bc3f82d626e /Documentation/networking
parenta26272e5200765691e67d6780e52b32498fdb659 (diff)
parent2ec8c6bb5d8f3a62a79f463525054bae1e3d4487 (diff)
Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next-2.6
* git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next-2.6: (1674 commits) qlcnic: adding co maintainer ixgbe: add support for active DA cables ixgbe: dcb, do not tag tc_prio_control frames ixgbe: fix ixgbe_tx_is_paused logic ixgbe: always enable vlan strip/insert when DCB is enabled ixgbe: remove some redundant code in setting FCoE FIP filter ixgbe: fix wrong offset to fc_frame_header in ixgbe_fcoe_ddp ixgbe: fix header len when unsplit packet overflows to data buffer ipv6: Never schedule DAD timer on dead address ipv6: Use POSTDAD state ipv6: Use state_lock to protect ifa state ipv6: Replace inet6_ifaddr->dead with state cxgb4: notify upper drivers if the device is already up when they load cxgb4: keep interrupts available when the ports are brought down cxgb4: fix initial addition of MAC address cnic: Return SPQ credit to bnx2x after ring setup and shutdown. cnic: Convert cnic_local_flags to atomic ops. can: Fix SJA1000 command register writes on SMP systems bridge: fix build for CONFIG_SYSFS disabled ARCNET: Limit com20020 PCI ID matches for SOHARD cards ... Fix up various conflicts with pcmcia tree drivers/net/ {pcmcia/3c589_cs.c, wireless/orinoco/orinoco_cs.c and wireless/orinoco/spectrum_cs.c} and feature removal (Documentation/feature-removal-schedule.txt). Also fix a non-content conflict due to pm_qos_requirement getting renamed in the PM tree (now pm_qos_request) in net/mac80211/scan.c
Diffstat (limited to 'Documentation/networking')
5 files changed, 573 insertions, 42 deletions
diff --git a/Documentation/networking/caif/Linux-CAIF.txt b/Documentation/networking/caif/Linux-CAIF.txt
new file mode 100644
index 0000000..7fe7a9a
--- /dev/null
+++ b/Documentation/networking/caif/Linux-CAIF.txt
@@ -0,0 +1,212 @@
+Linux CAIF
+copyright (C) ST-Ericsson AB 2010
+Author: Sjur Brendeland/ sjur.brandeland@stericsson.com
+License terms: GNU General Public License (GPL) version 2
+CAIF is a MUX protocol used by ST-Ericsson cellular modems for
+communication between Modem and host. The host processes can open virtual AT
+channels, initiate GPRS Data connections, Video channels and Utility Channels.
+The Utility Channels are general purpose pipes between modem and host.
+ST-Ericsson modems support a number of transports between modem
+and host. Currently, UART and Loopback are available for Linux.
+The implementation of CAIF is divided into:
+* CAIF Socket Layer, Kernel API, and Net Device.
+* CAIF Core Protocol Implementation
+* CAIF Link Layer, implemented as NET devices.
+ !
+ ! +------+ +------+ +------+
+ ! +------+! +------+! +------+!
+ ! ! Sock !! !Kernel!! ! Net !!
+ ! ! API !+ ! API !+ ! Dev !+ <- CAIF Client APIs
+ ! +------+ +------! +------+
+ ! ! ! !
+ ! +----------!----------+
+ ! +------+ <- CAIF Protocol Implementation
+ +-------> ! CAIF !
+ ! Core !
+ +------+
+ +--------!--------+
+ ! !
+ +------+ +-----+
+ ! ! ! TTY ! <- Link Layer (Net Devices)
+ +------+ +-----+
+Using the Kernel API
+The Kernel API is used for accessing CAIF channels from the
+The user of the API has to implement two callbacks for receive
+and control.
+The receive callback gives a CAIF packet as a SKB. The control
+callback will
+notify of channel initialization complete, and flow-on/flow-
+ struct caif_device caif_dev = {
+ .caif_config = {
+ .name = "MYDEV"
+ .type = CAIF_CHTY_AT
+ }
+ .receive_cb = my_receive,
+ .control_cb = my_control,
+ };
+ caif_add_device(&caif_dev);
+ caif_transmit(&caif_dev, skb);
+See the caif_kernel.h for details about the CAIF kernel API.
+I M P L E M E N T A T I O N
+CAIF Core Protocol Layer
+CAIF Core layer implements the CAIF protocol as defined by ST-Ericsson.
+It implements the CAIF protocol stack in a layered approach, where
+each layer described in the specification is implemented as a separate layer.
+The architecture is inspired by the design patterns "Protocol Layer" and
+"Protocol Packet".
+== CAIF structure ==
+The Core CAIF implementation contains:
+ - Simple implementation of CAIF.
+ - Layered architecture (a la Streams), each layer in the CAIF
+ specification is implemented in a separate c-file.
+ - Clients must implement PHY layer to access physical HW
+ with receive and transmit functions.
+ - Clients must call configuration function to add PHY layer.
+ - Clients must implement CAIF layer to consume/produce
+ CAIF payload with receive and transmit functions.
+ - Clients must call configuration function to add and connect the
+ Client layer.
+ - When receiving / transmitting CAIF Packets (cfpkt), ownership is passed
+ to the called function (except for framing layers' receive functions
+ or if a transmit function returns an error, in which case the caller
+ must free the packet).
+Layered Architecture
+The CAIF protocol can be divided into two parts: Support functions and Protocol
+Implementation. The support functions include:
+ - CFPKT CAIF Packet. Implementation of CAIF Protocol Packet. The
+ CAIF Packet has functions for creating, destroying and adding content
+ and for adding/extracting header and trailers to protocol packets.
+ - CFLST CAIF list implementation.
+ - CFGLUE CAIF Glue. Contains OS Specifics, such as memory
+ allocation, endianness, etc.
+The CAIF Protocol implementation contains:
+ - CFCNFG CAIF Configuration layer. Configures the CAIF Protocol
+ Stack and provides a Client interface for adding Link-Layer and
+ Driver interfaces on top of the CAIF Stack.
+ - CFCTRL CAIF Control layer. Encodes and Decodes control messages
+ such as enumeration and channel setup. Also matches request and
+ response messages.
+ - CFSERVL General CAIF Service Layer functionality; handles flow
+ control and remote shutdown requests.
+ - CFVEI CAIF VEI layer. Handles CAIF AT Channels on VEI (Virtual
+ External Interface). This layer encodes/decodes VEI frames.
+ - CFDGML CAIF Datagram layer. Handles CAIF Datagram layer (IP
+ traffic), encodes/decodes Datagram frames.
+ - CFMUX CAIF Mux layer. Handles multiplexing between multiple
+ physical bearers and multiple channels such as VEI, Datagram, etc.
+ The MUX keeps track of the existing CAIF Channels and
+ Physical Instances and selects the apropriate instance based
+ on Channel-Id and Physical-ID.
+ - CFFRML CAIF Framing layer. Handles Framing i.e. Frame length
+ and frame checksum.
+ - CFSERL CAIF Serial layer. Handles concatenation/split of frames
+ into CAIF Frames with correct length.
+ +---------+
+ | Config |
+ | CFCNFG |
+ +---------+
+ !
+ +---------+ +---------+ +---------+
+ | AT | | Control | | Datagram|
+ +---------+ +---------+ +---------+
+ \_____________!______________/
+ !
+ +---------+
+ | MUX |
+ | |
+ +---------+
+ _____!_____
+ / \
+ +---------+ +---------+
+ | Framing | | Framing |
+ +---------+ +---------+
+ ! !
+ +---------+ +---------+
+ | | | Serial |
+ | | | CFSERL |
+ +---------+ +---------+
+In this layered approach the following "rules" apply.
+ - All layers embed the same structure "struct cflayer"
+ - A layer does not depend on any other layer's private data.
+ - Layers are stacked by setting the pointers
+ layer->up , layer->dn
+ - In order to send data upwards, each layer should do
+ layer->up->receive(layer->up, packet);
+ - In order to send data downwards, each layer should do
+ layer->dn->transmit(layer->dn, packet);
+Linux Driver Implementation
+Linux GPRS Net Device and CAIF socket are implemented on top of the
+CAIF Core protocol. The Net device and CAIF socket have an instance of
+'struct cflayer', just like the CAIF Core protocol stack.
+Net device and Socket implement the 'receive()' function defined by
+'struct cflayer', just like the rest of the CAIF stack. In this way, transmit and
+receive of packets is handled as by the rest of the layers: the 'dn->transmit()'
+function is called in order to transmit data.
+The layer on top of the CAIF Core implementation is
+sometimes referred to as the "Client layer".
+Configuration of Link Layer
+The Link Layer is implemented as Linux net devices (struct net_device).
+Payload handling and registration is done using standard Linux mechanisms.
+The CAIF Protocol relies on a loss-less link layer without implementing
+retransmission. This implies that packet drops must not happen.
+Therefore a flow-control mechanism is implemented where the physical
+interface can initiate flow stop for all CAIF Channels.
diff --git a/Documentation/networking/caif/README b/Documentation/networking/caif/README
new file mode 100644
index 0000000..757ccfa
--- /dev/null
+++ b/Documentation/networking/caif/README
@@ -0,0 +1,109 @@
+Copyright (C) ST-Ericsson AB 2010
+Author: Sjur Brendeland/ sjur.brandeland@stericsson.com
+License terms: GNU General Public License (GPL) version 2
+=== Start ===
+If you have compiled CAIF for modules do:
+$modprobe crc_ccitt
+$modprobe caif
+$modprobe caif_socket
+$modprobe chnl_net
+=== Preparing the setup with a STE modem ===
+If you are working on integration of CAIF you should make sure
+that the kernel is built with module support.
+There are some things that need to be tweaked to get the host TTY correctly
+set up to talk to the modem.
+Since the CAIF stack is running in the kernel and we want to use the existing
+TTY, we are installing our physical serial driver as a line discipline above
+the TTY device.
+To achieve this we need to install the N_CAIF ldisc from user space.
+The benefit is that we can hook up to any TTY.
+The use of Start-of-frame-extension (STX) must also be set as
+module parameter "ser_use_stx".
+Normally Frame Checksum is always used on UART, but this is also provided as a
+module parameter "ser_use_fcs".
+$ modprobe caif_serial ser_ttyname=/dev/ttyS0 ser_use_stx=yes
+$ ifconfig caif_ttyS0 up
+PLEASE NOTE: There is a limitation in Android shell.
+ It only accepts one argument to insmod/modprobe!
+=== Trouble shooting ===
+There are debugfs parameters provided for serial communication.
+* ser_state: Prints the bit-mask status where
+ - 0x02 means SENDING, this is a transient state.
+ - 0x10 means FLOW_OFF_SENT, i.e. the previous frame has not been sent
+ and is blocking further send operation. Flow OFF has been propagated
+ to all CAIF Channels using this TTY.
+* tty_status: Prints the bit-mask tty status information
+ - 0x01 - tty->warned is on.
+ - 0x02 - tty->low_latency is on.
+ - 0x04 - tty->packed is on.
+ - 0x08 - tty->flow_stopped is on.
+ - 0x10 - tty->hw_stopped is on.
+ - 0x20 - tty->stopped is on.
+* last_tx_msg: Binary blob Prints the last transmitted frame.
+ This can be printed with
+ $od --format=x1 /sys/kernel/debug/caif_serial/<tty>/last_rx_msg.
+ The first two tx messages sent look like this. Note: The initial
+ byte 02 is start of frame extension (STX) used for re-syncing
+ upon errors.
+ - Enumeration:
+ 0000000 02 05 00 00 03 01 d2 02
+ | | | | | |
+ STX(1) | | | |
+ Length(2)| | |
+ Control Channel(1)
+ Command:Enumeration(1)
+ Link-ID(1)
+ Checksum(2)
+ - Channel Setup:
+ 0000000 02 07 00 00 00 21 a1 00 48 df
+ | | | | | | | |
+ STX(1) | | | | | |
+ Length(2)| | | | |
+ Control Channel(1)
+ Command:Channel Setup(1)
+ Channel Type(1)
+ Priority and Link-ID(1)
+ Endpoint(1)
+ Checksum(2)
+* last_rx_msg: Prints the last transmitted frame.
+ The RX messages for LinkSetup look almost identical but they have the
+ bit 0x20 set in the command bit, and Channel Setup has added one byte
+ before Checksum containing Channel ID.
+ NOTE: Several CAIF Messages might be concatenated. The maximum debug
+ buffer size is 128 bytes.
+== Error Scenarios:
+- last_tx_msg contains channel setup message and last_rx_msg is empty ->
+ The host seems to be able to send over the UART, at least the CAIF ldisc get
+ notified that sending is completed.
+- last_tx_msg contains enumeration message and last_rx_msg is empty ->
+ The host is not able to send the message from UART, the tty has not been
+ able to complete the transmit operation.
+- if /sys/kernel/debug/caif_serial/<tty>/tty_status is non-zero there
+ might be problems transmitting over UART.
+ E.g. host and modem wiring is not correct you will typically see
+ tty_status = 0x10 (hw_stopped) and ser_state = 0x10 (FLOW_OFF_SENT).
+ You will probably see the enumeration message in last_tx_message
+ and empty last_rx_message.
diff --git a/Documentation/networking/ip-sysctl.txt b/Documentation/networking/ip-sysctl.txt
index 8b72c88..d0536b5 100644
--- a/Documentation/networking/ip-sysctl.txt
+++ b/Documentation/networking/ip-sysctl.txt
@@ -588,6 +588,37 @@ ip_local_port_range - 2 INTEGERS
(i.e. by default) range 1024-4999 is enough to issue up to
2000 connections per second to systems supporting timestamps.
+ip_local_reserved_ports - list of comma separated ranges
+ Specify the ports which are reserved for known third-party
+ applications. These ports will not be used by automatic port
+ assignments (e.g. when calling connect() or bind() with port
+ number 0). Explicit port allocation behavior is unchanged.
+ The format used for both input and output is a comma separated
+ list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and
+ 10). Writing to the file will clear all previously reserved
+ ports and update the current list with the one given in the
+ input.
+ Note that ip_local_port_range and ip_local_reserved_ports
+ settings are independent and both are considered by the kernel
+ when determining which ports are available for automatic port
+ assignments.
+ You can reserve ports which are not in the current
+ ip_local_port_range, e.g.:
+ $ cat /proc/sys/net/ipv4/ip_local_port_range
+ 32000 61000
+ $ cat /proc/sys/net/ipv4/ip_local_reserved_ports
+ 8080,9148
+ although this is redundant. However such a setting is useful
+ if later the port range is changed to a value that will
+ include the reserved ports.
+ Default: Empty
ip_nonlocal_bind - BOOLEAN
If set, allows processes to bind() to non-local IP addresses,
which can be quite useful - but may break some applications.
diff --git a/Documentation/networking/l2tp.txt b/Documentation/networking/l2tp.txt
index 63214b2..e7bf397 100644
--- a/Documentation/networking/l2tp.txt
+++ b/Documentation/networking/l2tp.txt
@@ -1,44 +1,95 @@
-This brief document describes how to use the kernel's PPPoL2TP driver
-to provide L2TP functionality. L2TP is a protocol that tunnels one or
-more PPP sessions over a UDP tunnel. It is commonly used for VPNs
+This document describes how to use the kernel's L2TP drivers to
+provide L2TP functionality. L2TP is a protocol that tunnels one or
+more sessions over an IP tunnel. It is commonly used for VPNs
(L2TP/IPSec) and by ISPs to tunnel subscriber PPP sessions over an IP
-network infrastructure.
+network infrastructure. With L2TPv3, it is also useful as a Layer-2
+tunneling infrastructure.
+L2TPv2 (PPP over L2TP (UDP tunnels)).
+L2TPv3 ethernet pseudowires.
+L2TPv3 PPP pseudowires.
+L2TPv3 IP encapsulation.
+Netlink sockets for L2TPv3 configuration management.
+The original pppol2tp driver was introduced in 2.6.23 and provided
+L2TPv2 functionality (rfc2661). L2TPv2 is used to tunnel one or more PPP
+sessions over a UDP tunnel.
+L2TPv3 (rfc3931) changes the protocol to allow different frame types
+to be passed over an L2TP tunnel by moving the PPP-specific parts of
+the protocol out of the core L2TP packet headers. Each frame type is
+known as a pseudowire type. Ethernet, PPP, HDLC, Frame Relay and ATM
+pseudowires for L2TP are defined in separate RFC standards. Another
+change for L2TPv3 is that it can be carried directly over IP with no
+UDP header (UDP is optional). It is also possible to create static
+unmanaged L2TPv3 tunnels manually without a control protocol
+(userspace daemon) to manage them.
+To support L2TPv3, the original pppol2tp driver was split up to
+separate the L2TP and PPP functionality. Existing L2TPv2 userspace
+apps should be unaffected as the original pppol2tp sockets API is
+retained. L2TPv3, however, uses netlink to manage L2TPv3 tunnels and
-The PPPoL2TP driver, drivers/net/pppol2tp.c, provides a mechanism by
-which PPP frames carried through an L2TP session are passed through
-the kernel's PPP subsystem. The standard PPP daemon, pppd, handles all
-PPP interaction with the peer. PPP network interfaces are created for
-each local PPP endpoint.
-The L2TP protocol http://www.faqs.org/rfcs/rfc2661.html defines L2TP
-control and data frames. L2TP control frames carry messages between
-L2TP clients/servers and are used to setup / teardown tunnels and
-sessions. An L2TP client or server is implemented in userspace and
-will use a regular UDP socket per tunnel. L2TP data frames carry PPP
-frames, which may be PPP control or PPP data. The kernel's PPP
+The L2TP protocol separates control and data frames. The L2TP kernel
+drivers handle only L2TP data frames; control frames are always
+handled by userspace. L2TP control frames carry messages between L2TP
+clients/servers and are used to setup / teardown tunnels and
+sessions. An L2TP client or server is implemented in userspace.
+Each L2TP tunnel is implemented using a UDP or L2TPIP socket; L2TPIP
+provides L2TPv3 IP encapsulation (no UDP) and is implemented using a
+new l2tpip socket family. The tunnel socket is typically created by
+userspace, though for unmanaged L2TPv3 tunnels, the socket can also be
+created by the kernel. Each L2TP session (pseudowire) gets a network
+interface instance. In the case of PPP, these interfaces are created
+indirectly by pppd using a pppol2tp socket. In the case of ethernet,
+the netdevice is created upon a netlink request to create an L2TPv3
+ethernet pseudowire.
+For PPP, the PPPoL2TP driver, net/l2tp/l2tp_ppp.c, provides a
+mechanism by which PPP frames carried through an L2TP session are
+passed through the kernel's PPP subsystem. The standard PPP daemon,
+pppd, handles all PPP interaction with the peer. PPP network
+interfaces are created for each local PPP endpoint. The kernel's PPP
subsystem arranges for PPP control frames to be delivered to pppd,
while data frames are forwarded as usual.
+For ethernet, the L2TPETH driver, net/l2tp/l2tp_eth.c, implements a
+netdevice driver, managing virtual ethernet devices, one per
+pseudowire. These interfaces can be managed using standard Linux tools
+such as "ip" and "ifconfig". If only IP frames are passed over the
+tunnel, the interface can be given an IP addresses of itself and its
+peer. If non-IP frames are to be passed over the tunnel, the interface
+can be added to a bridge using brctl. All L2TP datapath protocol
+functions are handled by the L2TP core driver.
Each tunnel and session within a tunnel is assigned a unique tunnel_id
and session_id. These ids are carried in the L2TP header of every
-control and data packet. The pppol2tp driver uses them to lookup
-internal tunnel and/or session contexts. Zero tunnel / session ids are
-treated specially - zero ids are never assigned to tunnels or sessions
-in the network. In the driver, the tunnel context keeps a pointer to
-the tunnel UDP socket. The session context keeps a pointer to the
-PPPoL2TP socket, as well as other data that lets the driver interface
-to the kernel PPP subsystem.
-Note that the pppol2tp kernel driver handles only L2TP data frames;
-L2TP control frames are simply passed up to userspace in the UDP
-tunnel socket. The kernel handles all datapath aspects of the
-protocol, including data packet resequencing (if enabled).
-There are a number of requirements on the userspace L2TP daemon in
-order to use the pppol2tp driver.
+control and data packet. (Actually, in L2TPv3, the tunnel_id isn't
+present in data frames - it is inferred from the IP connection on
+which the packet was received.) The L2TP driver uses the ids to lookup
+internal tunnel and/or session contexts to determine how to handle the
+packet. Zero tunnel / session ids are treated specially - zero ids are
+never assigned to tunnels or sessions in the network. In the driver,
+the tunnel context keeps a reference to the tunnel UDP or L2TPIP
+socket. The session context holds data that lets the driver interface
+to the kernel's network frame type subsystems, i.e. PPP, ethernet.
+Userspace Programming
+For L2TPv2, there are a number of requirements on the userspace L2TP
+daemon in order to use the pppol2tp driver.
1. Use a UDP socket per tunnel.
@@ -86,6 +137,35 @@ In addition to the standard PPP ioctls, a PPPIOCGL2TPSTATS is provided
to retrieve tunnel and session statistics from the kernel using the
PPPoX socket of the appropriate tunnel or session.
+For L2TPv3, userspace must use the netlink API defined in
+include/linux/l2tp.h to manage tunnel and session contexts. The
+general procedure to create a new L2TP tunnel with one session is:-
+1. Open a GENL socket using L2TP_GENL_NAME for configuring the kernel
+ using netlink.
+2. Create a UDP or L2TPIP socket for the tunnel.
+3. Create a new L2TP tunnel using a L2TP_CMD_TUNNEL_CREATE
+ request. Set attributes according to desired tunnel parameters,
+ referencing the UDP or L2TPIP socket created in the previous step.
+4. Create a new L2TP session in the tunnel using a
+The tunnel and all of its sessions are closed when the tunnel socket
+is closed. The netlink API may also be used to delete sessions and
+tunnels. Configuration and status info may be set or read using netlink.
+The L2TP driver also supports static (unmanaged) L2TPv3 tunnels. These
+are where there is no L2TP control message exchange with the peer to
+setup the tunnel; the tunnel is configured manually at each end of the
+tunnel. There is no need for an L2TP userspace application in this
+case -- the tunnel socket is created by the kernel and configured
+using parameters sent in the L2TP_CMD_TUNNEL_CREATE netlink
+request. The "ip" utility of iproute2 has commands for managing static
+L2TPv3 tunnels; do "ip l2tp help" for more information.
@@ -102,6 +182,69 @@ PPPOL2TP_MSG_CONTROL userspace - kernel interface
PPPOL2TP_MSG_SEQ sequence numbers handling
PPPOL2TP_MSG_DATA data packets
+If enabled, files under a l2tp debugfs directory can be used to dump
+kernel state about L2TP tunnels and sessions. To access it, the
+debugfs filesystem must first be mounted.
+# mount -t debugfs debugfs /debug
+Files under the l2tp directory can then be accessed.
+# cat /debug/l2tp/tunnels
+The debugfs files should not be used by applications to obtain L2TP
+state information because the file format is subject to change. It is
+implemented to provide extra debug information to help diagnose
+problems.) Users should use the netlink API.
+/proc/net/pppol2tp is also provided for backwards compaibility with
+the original pppol2tp driver. It lists information about L2TPv2
+tunnels and sessions only. Its use is discouraged.
+Unmanaged L2TPv3 Tunnels
+Some commercial L2TP products support unmanaged L2TPv3 ethernet
+tunnels, where there is no L2TP control protocol; tunnels are
+configured at each side manually. New commands are available in
+iproute2's ip utility to support this.
+To create an L2TPv3 ethernet pseudowire between local host
+and peer, using IP addresses and for the
+tunnel endpoints:-
+# modprobe l2tp_eth
+# modprobe l2tp_netlink
+# ip l2tp add tunnel tunnel_id 1 peer_tunnel_id 1 udp_sport 5000 \
+ udp_dport 5000 encap udp local remote
+# ip l2tp add session tunnel_id 1 session_id 1 peer_session_id 1
+# ifconfig -a
+# ip addr add peer dev l2tpeth0
+# ifconfig l2tpeth0 up
+Choose IP addresses to be the address of a local IP interface and that
+of the remote system. The IP addresses of the l2tpeth0 interface can be
+anything suitable.
+Repeat the above at the peer, with ports, tunnel/session ids and IP
+addresses reversed. The tunnel and session IDs can be any non-zero
+32-bit number, but the values must be reversed at the peer.
+Host 1 Host2
+udp_sport=5000 udp_sport=5001
+udp_dport=5001 udp_dport=5000
+tunnel_id=42 tunnel_id=45
+peer_tunnel_id=45 peer_tunnel_id=42
+session_id=128 session_id=5196755
+peer_session_id=5196755 peer_session_id=128
+When done at both ends of the tunnel, it should be possible to send
+data over the network. e.g.
+# ping
Sample Userspace Code
@@ -158,12 +301,48 @@ Sample Userspace Code
return 0;
+Internal Implementation
+The driver keeps a struct l2tp_tunnel context per L2TP tunnel and a
+struct l2tp_session context for each session. The l2tp_tunnel is
+always associated with a UDP or L2TP/IP socket and keeps a list of
+sessions in the tunnel. The l2tp_session context keeps kernel state
+about the session. It has private data which is used for data specific
+to the session type. With L2TPv2, the session always carried PPP
+traffic. With L2TPv3, the session can also carry ethernet frames
+(ethernet pseudowire) or other data types such as ATM, HDLC or Frame
+When a tunnel is first opened, the reference count on the socket is
+increased using sock_hold(). This ensures that the kernel socket
+cannot be removed while L2TP's data structures reference it.
+Some L2TP sessions also have a socket (PPP pseudowires) while others
+do not (ethernet pseudowires). We can't use the socket reference count
+as the reference count for session contexts. The L2TP implementation
+therefore has its own internal reference counts on the session
+To Do
+Add L2TP tunnel switching support. This would route tunneled traffic
+from one L2TP tunnel into another. Specified in
+Add L2TPv3 VLAN pseudowire support.
+Add L2TPv3 IP pseudowire support.
+Add L2TPv3 ATM pseudowire support.
-The PPPoL2TP driver was developed as part of the OpenL2TP project by
+The L2TP drivers were developed as part of the OpenL2TP project by
Katalix Systems Ltd. OpenL2TP is a full-featured L2TP client / server,
designed from the ground up to have the L2TP datapath in the
kernel. The project also implemented the pppol2tp plugin for pppd
which allows pppd to use the kernel driver. Details can be found at
diff --git a/Documentation/networking/x25-iface.txt b/Documentation/networking/x25-iface.txt
index 975cc87..78f662e 100644
--- a/Documentation/networking/x25-iface.txt
+++ b/Documentation/networking/x25-iface.txt
@@ -20,23 +20,23 @@ the rest of the skbuff, if any more information does exist.
Packet Layer to Device Driver
-First Byte = 0x00
+First Byte = 0x00 (X25_IFACE_DATA)
This indicates that the rest of the skbuff contains data to be transmitted
over the LAPB link. The LAPB link should already exist before any data is
passed down.
-First Byte = 0x01
+First Byte = 0x01 (X25_IFACE_CONNECT)
Establish the LAPB link. If the link is already established then the connect
confirmation message should be returned as soon as possible.
-First Byte = 0x02
+First Byte = 0x02 (X25_IFACE_DISCONNECT)
Terminate the LAPB link. If it is already disconnected then the disconnect
confirmation message should be returned as soon as possible.
-First Byte = 0x03
+First Byte = 0x03 (X25_IFACE_PARAMS)
LAPB parameters. To be defined.
@@ -44,22 +44,22 @@ LAPB parameters. To be defined.
Device Driver to Packet Layer
-First Byte = 0x00
+First Byte = 0x00 (X25_IFACE_DATA)
This indicates that the rest of the skbuff contains data that has been
received over the LAPB link.
-First Byte = 0x01
+First Byte = 0x01 (X25_IFACE_CONNECT)
LAPB link has been established. The same message is used for both a LAPB
link connect_confirmation and a connect_indication.
-First Byte = 0x02
+First Byte = 0x02 (X25_IFACE_DISCONNECT)
LAPB link has been terminated. This same message is used for both a LAPB
link disconnect_confirmation and a disconnect_indication.
-First Byte = 0x03
+First Byte = 0x03 (X25_IFACE_PARAMS)
LAPB parameters. To be defined.

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