[Swan] releasing old connection to free the route

[Paul Wouters]

On Mon, 24 Jan 2022, Christoph Litauer wrote:

> I use libreswan 3.29 on an Ubuntu 20.04.3 LTS.
>
> Until now we had a l2tp-setup using openswan 2.6.49 on an ubuntu 16.04.7. No problems, we had hundreds of users in parallel. Some of these users by accident use the same local ip address.
>
> For security we have to upgrade to Ubuntu 20 and thus had to change to libreswan. Setup is nearly identical. But now we have a serious problem: 
> - User A uses local ip 192.168.55.45 behind NAT. Public IP is 87.156.203.224 
> - User B uses local ip 192.168.55.45 behind NAT. Public IP is 185.66.195.84
>
> A starts the tunnel. As soon es B starts his tunnel, the tunnel for A is terminated and vice versa.

Do they use a unique ID or are these clients that pick their native IP
as ID? If so, they would both share the same ID 192.168.55.45 and
libreswan would assume this is a reconnect. The libreswan behaviour
depends a bit on whether certs or PSKs are used.

You can try setting uniqueids=no in "config setup" because I believe
Windows clients do use their pre-NAT IP as the ID for l2tp.

A more modern solution would be to migrate to IKEv2 and avoid the
whole problem of transport mode and virtual-private= and L2TP
protocol overhead.

I would be interested in a full debug log of this event of a second
client connecting with both openswan and libreswan if you can, so
I can better understand the differece and if there is a libreswan
mitigation we can do.

Paul