ipsec on additional IP

Hi,

we have an ASG 8.305 with a External WAN Interface with a primary IP and three additional IPs.
We want some User to connect to one of the additional IPs with a ipsec Client software.
Our problem is that the ipsec connection only work with the primary IP of that interface.
Is there any solution to get ipsec working on an additional IP?

We have three RED devices which successfuly connect to an additional IP.
So is it possible for the Users making a ipsec connection to an additional IP?

Bjoern