[Swan] releasing old connection to free the route

Christoph Litauer litauer at uni-koblenz.de
Tue Jan 25 10:00:11 EET 2022

Paul, thanks a lot for your quick response.

I checked the log. Indeed, the peer id is the native ip. We already had uniqueids=no but we are using PSK. According to the manpage this setting ist ignored when authby=secret is used.
I should have mentioned, that the described behaviour belongs solely to windows clients (we think so, but did not check very hard).

Today, I am not able to create a new test case on the openswan server, will do tomorrow. Here you can find libreswan.log and my ipsec.conf:

Will upload an openswan.log as soon as we have it.

> Am 24.01.2022 um 16:52 schrieb Paul Wouters <paul.wouters at aiven.io>:
> 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 behind NAT. Public IP is - User B uses local ip behind NAT. Public IP is
>> 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 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

Freundliche Grüße
Christoph Litauer
Christoph Litauer
Uni Koblenz, Rechenzentrum, Raum A 022    
Postfach 201602, 56016 Koblenz     
Fon: +49 261 287-1311, Fax: -100 1311

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