[Openswan Users] Statement on support of multiple clients using transport mode and L2TP

Patrick Naubert patrickn at xelerance.com
Wed May 10 13:24:41 CEST 2006

Statement on support of multiple clients using transport mode and L2TP

Currently Openswan, both with KLIPS and NETKEY, will show unexpected  
behavior with the use of NAPT/NAT (IP Masquerading) at either the  
source end or destination end, combined with transport mode.

Many users have reported problems on the Openswan mailing lists.   
Xelerance has been aware of these issues even before the users  
started experimenting with using Openswan in transport mode.  
Transport mode is necessary with the use of L2TP to connect from a  
Windows (or OSX) platform to an Openswan server, using Windows (or  
OSX) native IPsec clients.

A few issues with NAT support and MTU problems appeared at the time  
of the 2.4.x series, which muddied the waters a bit. Work arounds for  
OSX and Windows had to be added to the NAT-detection in pluto code,  
and some problems in "vhost" code as well as some NAT related rekey  
errors showed up during at this time.

The NAT detection fixes were merged into the current 2.4 series.  The  
"vhost" patches are being merged into the development public code.  
They will be rolled into a numbered release in the future.

Here is where the Openswan software stands at this time:

NETKEY uses the external IP as an SA identifier.  Kernel magic is  
used to support this.  This means that multiple clients connecting  
from behind the same home firewall will not work. One will, but not  
multiple. This also means that multiple home users will be able to  
connect from behind their respective firewalls at the same time, as  
long as they are alone at their origin. Also, workarounds needed to  
be added to ensure one L2TP/IPsec and other non-encrypted clients  
from behind the same NAT router would work. This is an important  
issue in some of the larger deployed GPRS networks.

KLIPS uses the internal IP as an SA identifier. This means that  
multiple clients connecting from behind the same home firewall could  
work, but a additional policy bug in the 2.4.x versions actually made  
this functionality undependable, particularly when using templated X. 
509 based connections.

The current KLIPS logic also meant that multiple home users could not  
connect to an Openswan server if each was using the same source IP;  
this is very common as Linksys routers will issue DHCP address from and up.

Chances are that each of your 100+ home users connecting to your  
Openswan server will have as a source IP address from  
behind the Linksys. Netgear and others have the same problem.

The result is that the L2TP server residing on the Openswan server  
has no way of uniquely identifying multiple users using the same  
source IP, regardless of which IPsec stack is used.

Our solution was to modify KLIPS, pluto, iptables and l2tpd.
There is a new API interface between KLIPS and l2tpd, mediated by the  
IP and UDP socket layers.

We forked the l2tpd project, since the current l2tpd developers did  
not respond to our emails nor process our patches. Our fork is named  
xl2tpd. It is hosted at our site. The new option "ipsec saref"  
enables the new API interface functionality. The iptables changes  
have been submitted to upstream for inclusion. The pluto code was re- 
factored to better handle NAT-T, and fixed some of the "vhost" bugs  
related to the Virtual IP selection and rekeying.

All told, Xelerance spent $70,000US of development time to create  
this functionality.  We did this because a sponsor approached us to  
create the functionality.  The unfortunate thing was that the sponsor  
could only cover a fraction of the development cost.

The functionality has been delivered to the sponsor, and is being  
used at this time internal to the sponsor.

The good news is that the resulting API into userland forms the basis  
of some work that is relevant to the IETF BTNS workgroup's efforts  

The bad news is that Xelerance will not release this Openswan  
functionality into the general code base until such time as our  
development costs have been covered by sponsors.

We are looking for $55,000US from the community.

As a company, if you are interested in sponsoring this functionality,  
please contact us immediately.  As an individual, if you are  
interested in sponsoring this functionality, you will most probably  
have to approach other individual users and pool your resources.

We hope to be able to start work on our next project soon, which is  
the "merging" of the KLIPS and NETKEY to provide one unified stack  
that is satisfactory to both the Linux kernel maintainers and the  
IPsec endusers.

You can reach us at sales at xelerance.com

Thank you

Patrick Naubert
Chief Executive Officer, Xelerance Corporation

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