WHMCS Integration - what IP is used to access the Remote Host?

Hi guys

What IP address is used to access the WHMCS Remote Host when a client accesses his client area via the WHMCS Integration front-end?

I want to redirect all the requests to the WHMCS installation to the WHMCS Integration client area. However, when I do this the WHMCS Integration plugin breaks as it's request to access the WHMCS installation is also redirected.

In order to overcome this problem I thought it makes sense to filter on IP addresses. For example, if a client tries accesses the WHMCS Integration front-end for the client area, what IP is being used to actually access the WHMCS installation?

If this method of redirecting clients without breaking the WHMCS Integration is not credible, can anyone propose a method that will actually work. The reason for doing this is that I prefer clients to have access to only one consistent client area.

Thanks for any help!
Johann