origreadme

第二层隧道模块l2tp源码,开发环境为linux

l2tpd version 0.60
==================
Copyright (C)1998 Adtran, Inc.
Mark Spencer <[e-mail]>

Introduction:
-------------

l2tpd is an implementation of the layer two tunneling protocol.  It works in
userspace completely (although kernel work is planned after the userspace
version is stablized).  l2tpd works by opening a pseudo-tty for communicating
with pppd.  Although l2tpd was written for Linux, the current version should
be highly portable to other UNIX's supported by pppd.

Legal: 
------ 
l2tpd is free software, distributed under the GNU General Public License (GPL)
and you should read the LICENSE File if you are not already familiar with the
GPL before using the product.

If you distribute l2tpd, a modified version, or a derivative product,  you
MUST not remove Adtran's name from the product nor modify the terms of the
copyright.

Adtran may license l2tpd under other terms in addition to the GPL.  This way,
companies who wish to use l2tpd for embedded systems or commercial applications
and find the GPL too restrictive can license the technology from Adtran under
more favorable terms.

Bugs, Patches, and Code Contribution:
-------------------------------------
Please send bug reports and patches to either the l2tp mailng list 
([e-mail]) or myself ([e-mail]).

In order to contribute code, either with patches, or by direct access to the
CVS tree for l2tpd, send me e-mail ([e-mail]).  

The word "FIXME" is a place holder for code that needs to be in place, or
checks that need to be done, but haven't been coded yet.  Feel free to fix the
fixme's and submit patches!

Adtran requires that you not restrict the licensing of any patches or code
contributions to the main l2tpd project (beyond the terms that are already
there).  This is to maintain our ability to distribute l2tpd as described
above.  It does not in any way affect your ability to use code that you have
written.

Of course, the above patch rules apply only to the "official" l2tpd product
as distributed by Adtran.  If you are unwilling to give Adtran the right to
re-license your patches under other terms than GPL, you may create your own
third party product which is distributed only under GPL.

Release Notes
-------------
Version 0.60 should be considered ALPHA.  It does NOT completely implement
the l2tp draft specification.  Work on the high-speed kernel
implementation has already begun, but a relase date is not available.

The primary use of this ALPHA level code is to test the ability of l2tpd
to talk with other LAC and LNS implementations.  I hope that everyone who
tests the software will send me results on how it worked or failed to work
for them.  

(theoretically) implemented features
------------------------------------
* Proper payload and control packet handling
* Reliable control packet delivery
* Ability to recover from payload errors
* Ability to handle packets with/without length set
* Ability to handle flow control or no flow control
* Most critical AVP's for normal operation
* Challenge authentication
* Hidden AVP's
* Hello's to detect outages
* Handles sync and async packets
* Can act as LNS
* Can be a source of a virtual LAC call
* Reads configuration file
* Automated LAC dialup via config file, including redial
* Can be configured while running via a file system pipe
* Access Control
* Statistics report when sent a SIGUSR1
* ACCM

Major unimplemented specification features
------------------------------------------
* Rate Adaptive Timeouts
* Out of order packet handling
* Initial/Final LCP states
* Q.931 Result Codes
* Tie Breakers
* Minimum/Maximum BPS
* Call Errors

Important non-specification related features to be added
--------------------------------------------------------
* More configuration options if needed
* Kernel support for *much* improved performance

Usage notes on /var/run/l2tp-control
------------------------------------
There aren't any command line options to l2tpd yet.

Upon running l2tpd, a pipe is created in /var/run/l2tp-control.  Simple
commands can then be echoed to this pipe to control l2tp on the fly.  The
commands are:  

t <host> - create a tunnel to <host>
c <tid> or <entry> - originate an l2tp call on the tunnel
  identified locally by <tid>, or dial the entry <entry>
h <cid> - hang up a call with the local identifier <cid>
d <tid> or <entry> - disconnect the tunnel locally identified by <tid>
  or a lac entry <entry>

For example, to establish a tunnel to marko.net, one might do:

echo "t marko.net" >/var/run/l2tp-control

l2tpd must be running for this to work.

Various other notes
-------------------
The PPP options are hard coded in l2tp.h until a file format is decided upon.
Sending a SIGUSR1 to l2tpd will cause it to dump its status.

Mailing List
------------
If you would like to contribute to discussions of the architecture of l2tpd,
file formats, etc, I encourage you to join the l2tpd mailing list by sending
the word "subscribe" in the body of a message to "[e-mail]"