Go to "Configuration > Object > Certificates". You can create a new certificate using "Add".

Enter a name for the new certificate, enter a host domain name for the ZyWALL (doesn't need to actually exist) and create a self-signed certificate with 2048 bit RSA.

Certificate creation takes up to 5 minutes.

Open the detailed data of the certificate using "Edit".

Copy the certificate in PEM format to the clipboard.

Paste the certificate from the clipboard into the Intra2net system under "System > Keys > Foreign keys".

Under IPSec ID, select just the DNS host name, not the certificate holder ("/CN=" etc.).

Export your own certificate from the Intra2net system as a .pem file (Under "System > Keys > Own keys", Data tab.

Import the Intra2net system certificate into ZyWALL, under the menu "Configuration > Object > Certificate", tab Trusted Certificates. Click "Import" below.

Select the directory in which you have saved the certificate of the Intra2net system.

The Intra2net system certificate is now displayed as a Trusted Certificate.