Add L2TP support.

Patch from James Chapman.

This patch adds support for L2TP. It allows pppd to interface with the
pppol2tp driver in the Linux kernel. All data packets are handled by
the Linux kernel in order that the datapath be as efficient as
possible, while a userspace daemon implements the L2TP control
protocol, handling tunnel/session setup and teardown. The
implementation uses the PPPoX infrastructure; the architecture is
similar to PPPoE/PPPoATM in that a userspace daemon spawns a pppd
process per PPP session and uses a protocol-specific plugin to connect
pppd with the kernel.

The pppol2tp Linux kernel driver was integrated in the Linux kernel
from 2.6.23. For earlier kernels, an out of tree driver is available
from the pppol2tp-kmod package on the OpenL2TP project site at
http://sourceforge.net/projects/openl2tp.

Signed-off-by: James Chapman <jchapman@katalix.com>

1 files changed, 66 insertions, 0 deletions

diff --git a/README.pppol2tp b/README.pppol2tp
new file mode 100644
index 0000000..f34e89f
--- /dev/null
+++ b/README.pppol2tp
@@ -0,0 +1,66 @@
+PPPoL2TP plugin
+===============
+
+The pppol2tp plugin lets pppd use the Linux kernel driver pppol2tp.ko
+to pass PPP frames in L2TP tunnels. The driver was integrated into the
+kernel in the 2.6.23 release. For kernels before 2.6.23, an
+out-of-tree kernel module is available from the pppol2tp-kmod package
+in the OpenL2TP project.
+
+Note that pppd receives only PPP control frames over the PPPoL2TP
+socket; data frames are handled entirely by the kernel.
+
+The pppol2tp plugin adds extra arguments to pppd and uses the Linux kernel
+PPP-over-L2TP driver to set up each session's data path.
+
+Arguments are:-
+
+pppol2tp <fd>                   - FD for PPPoL2TP socket
+pppol2tp_lns_mode               - PPPoL2TP LNS behavior. Default off.
+pppol2tp_send_seq               - PPPoL2TP enable sequence numbers in
+                                  transmitted data packets. Default off.
+pppol2tp_recv_seq               - PPPoL2TP enforce sequence numbers in
+                                  received data packets. Default off.
+pppol2tp_reorderto <millisecs>  - PPPoL2TP data packet reorder timeout.
+                                  Default 0 (no reordering).
+pppol2tp_debug_mask <mask>      - PPPoL2TP debug mask. Bitwise OR of
+				  1 - verbose debug
+				  2 - control
+				  4 - kernel transport
+				  8 - ppp packet data
+				  Default: 0 (no debug).
+pppol2tp_ifname <ifname>	- Name of PPP network interface visible
+				  to "ifconfig" and "ip link".
+				  Default: "pppN"
+pppol2tp_tunnel_id <id>		- L2TP tunnel_id tunneling this PPP
+				  session.
+pppol2tp_session_id <id>	- L2TP session_id of this PPP session.
+				  The tunnel_id/session_id pair is used
+				  when sending event messages to openl2tpd.
+
+pppd will typically be started by an L2TP daemon for each L2TP sesion,
+supplying one or more of the above arguments as required. The pppd
+user will usually have no visibility of these arguments.
+
+Two hooks are exported by this plugin.
+
+void (*pppol2tp_send_accm_hook)(int tunnel_id, int session_id,
+     uint32_t send_accm, uint32_t recv_accm);
+void (*pppol2tp_ip_updown_hook)(int tunnel_id, int session_id, int up);
+
+Credits
+=======
+
+This plugin was developed by Katalix Systems as part of the OpenL2TP
+project, http://openl2tp.sourceforge.net. OpenL2TP is a full-featured
+L2TP client-server, suitable for use as an enterprise L2TP VPN server
+or a VPN client.
+
+Please copy problems to the OpenL2TP mailing list:
+openl2tp-users@lists.sourceforge.net.
+
+Maintained by:
+	James Chapman
+	jchapman@katalix.com
+	Katalix Systems Ltd
+	http://www.katalix.com