VPN Fusion and firewall/port forwarding

[qpeg]

I have a question regarding VPN Fusion connections and how they interact with firewall rules / port forwarding. I've tried searching but come up with nothing relevant.

I'll be changing ISP soon to one that uses CG-NAT. From what I've read, this will very likely interfere with a VOIP (SIP based) service I'll also be getting soon. The VOIP provider has a solution to this however - they offer a cheap LT2P service that the VOIP connection can be routed over, bypassing the CG-NAT and giving the VOIP service a static IP without anything interfering with incoming traffic.

I can see that setting up the L2TP connection with VPN Fusion and setting the VOIP adapter to use that connection will be easy enough, but I also need to forward traffic from a range of IPs and ports (ie. my VOIP provider) to the VOIP adapter. Ideally any traffic other than that should be blocked for security reasons. So just to clarify, certain traffic on the L2TP connection needs to be forwarded to the VOIP adapter, and the rest blocked. Can I setup these rules for port forwarding just the same as I would for a normal connection, or do they not apply to VPN connections?

Any guidance appreciated.