The free L2TP implementation for Linux


11-12-1998: Version 0.60 released.
09-29-1998: Solaris support in CVS tree.
08-23-1998: Generic PPP patches available.
05-21-1998: Midnight Networks joins sponsor list.
05-21-1998: First alpha release available here.
05-21-1998: Successful interop with Zyxel
05-09-1998: Hidden AVP’s supported
05-08-1998: Tunnel Authentication Working
05-07-1998: Initial FreeBSD port
05-07-1998: Pulsecom joins sponsor list
05-04-1998: Successful interoperability with Cisco router
05-02-1998: initial work on configuration file
04-30-1998: packet buffering increases performance by 1000%
04-21-1998: l2tpd talks to itself!
04-20-1998: Migration to new scheduler
04-13-1998: New scheduling code added
04-08-1998: Control Re-transmission revamped
04-06-1998: De-threaded l2tpd functioning. More stable than threaded version
04-03-1998: Initial ideas for file format
04-02-1998: Welcome aboard, Nortel!

Introduction to L2TP:

Layer two tunneling protocol is a method for encapsulating standard PPP through a variety of media. The protocol also allows encapsulation of PPP using UDP packets. The draft specification for l2tp can be found here. The two most practical uses of L2TP are:
Establishment of virtual private networks
Ability to separate the devices which physically accept calls (say a modem or an ISDN termination) from the device which terminates the PPP call (say a centralized server.)
L2TP consists of two pieces: the L2TP Access Concentrator (LAC) and the L2TP Network Server (LNS). The LAC is the device which physically terminates a call. The LNS is the part which terminates and probably authenticates the PPP stream.

What is this project?

Adtran, Inc. is providing support for an Open Source implementation of L2TP. This technology will have very important effects upon the way remote access is handled. The final product will be distributed under the terms of the GNU GPL. Commercial support may be provided by Adtran and others, if commercially feasable. If you’re interested in commercial support, e-mail Mark Spencer.
The focus is primarily on creating an LNS since this is where the most work needs to be done, however l2tpd currently has LAC functionality as well. The L2TP daemon is a technology which is necessary for enabling the widespread use of L2TP.
The initial work is being done on RedHat Linux 5.0 and will consist of a completely userspace program which will act as a “front end” to pppd. The goal of the first release will be to achieve functionality with portablility to other UNIX operating systems. FreeBSD is also supported, but relatively untested.
The second release will be a heavily kernel based implementation. Although this part will be fairly specific to Linux (we will still encourage porting the new system to other OS’s, of course), we believe we will achieve optimal performance.

Why a free implementation?

Free software such as the Linux OS and the Apache web server have shown themselves to be among the fastest and most stable products available. Adtran is supporting this free software effort. This project will benefit from the open development model since there is widespread industry interest in this technology. We encourage other companies to support this effort.

How far along is the project?

As of May 9, we have well running code, and an alpha release is expected in the coming weeks, after some more interoperability testing.
However, there are many remaining TODO’s:
Rate Adaptive Timeouts
Support for initial/final LCP states]
Proxy authentication
Do something with private groups (?)
Kernel work (for the second release)

How can I participate?

There are several ways you can participate, and you don’t have to be a programmer to contribute.
Tell us what kind of features you would like to have
Give us a few words of support
Individual contributors are welcome, and/or get you company to support our work as Adtran does.
Provide resources for interoperability testing
If you would like to do some actual coding, a CVS tree has been setup to allow multiple programmers to work with the sources. For more information on access to the CVS tree, you may mail me, Mark Spencer.

How can I remain updated? Where can I find more information?

The best thing you can do is to join the l2tpd mailing list by sending mail to with the word “subscribe” in the body.
The mailing list will be archived here.
Corporate Sponsors
Adtran designs, develops, and manufactures ADvanced TRANsmission products for high speed digital communications products
Midnight Networks develops interoperability and remote access test systems, testing performance and capacity, to internetworking vendors, ISPs, telecommunications companies, and network managers. products
Nortel is a leading global provider of communications network solutions products
Pulsecom is a telecommunications solutions provider specializing in telephony technology both domestic and international, and data access products.