No SSH to my server possible

Symptoms: I have a server, to which I have an OpenSWAN IPsec connection, and I also use ssh sometimes. Now my client has rebooted, and the IPsec connection remains down, while I cannot ssh to the server any more. The server is still up, and via other machines I can still access it, with ssh too, just not from this particular client.

It turns out that on the server, the IPsec daemon is so busy trying to reconnect, using the SSH port, that the client never gets its request through.