OpenL2TP software is Dual Licensed. Users can choose to use the OpenL2TP software as an Open Source/Free Software product under the terms of the GNU General Public License (http://www.fsf.org/licenses/) or can purchase a commercial license.
The OpenL2TP software is released under the GNU General Public License (GPL). This means that the OpenL2TP software can be used free of charge under the terms of the GPL license. If you do not want to be bound by the GPL terms (such as the requirement that your application must also be GPL), you may purchase a commercial license for the same product from Katalix Systems Ltd. Since Katalix Systems Ltd owns the copyright to the OpenL2TP source code, we are able to employ Dual Licensing, which means that the same product is available under GPL and under a commercial license. This does not in any way affect the Open Source commitment of Katalix Systems Ltd.
Users cannot change the vendor string which is published in the L2TP control message protocol without purchasing a commercial license. For all GPL installations, the vendor string shall be "Katalix Systems Ltd. Linux".
The OpenL2TP software is released under the GNU General Public License (GPL). The formal terms of the GPL license can be found at http://www.fsf.org/licenses/. See also http://www.fsf.org/licenses/gpl-faq.html.
The GPL license is contagious in the sense that when a program is linked to a GPL program, all the source code for all the parts of the resulting product must also be released under the GPL. If you do not follow this GPL requirement, you break the license terms and forfeit your right to use the GPL program altogether. You also risk damages. You need a commercial license under these conditions:
- When you link a program with any GPL code from the OpenL2TP software and don't want the resulting product to be licensed under GPL, perhaps because you want to build a commercial product or keep the added non-GPL code closed source for other reasons. When purchasing commercial licenses, you are not using the OpenL2TP software under GPL even though it's the same code.
- When you distribute a non-GPL application that works only with the OpenL2TP software and ship it with the OpenL2TP software. This type of solution is considered to be linking even if it's done over a network.
- When you distribute copies of the OpenL2TP software without providing the source code as required under the GPL license.
- When you change the advertised L2TP vendor string.
A special exception is made for OpenL2TP plugins. Such plugins may be closed source and not come under GPL provided that they use OpenL2TP's standard plugin interface. It is not permitted to make open source changes to OpenL2TP in order to add new interfaces to OpenL2TP and then write a closed source plugin that uses the new interface.