Configure IPSec over UDP:

On the VPN Concentrator, select Configuration > User Management > Groups.

To add a group, select Add. To modify an existing group, select it and click Modify.

Click the IPSec tab, check IPSec through NAT and configure the IPSec through NAT UDP Port. The default port for IPSec through NAT is 10000 (source and destination), but this setting may be changed