Connection fails

[KuroNecron]

Greetings, maybe this is the wrong place to post/ask this, but i am at my wits' end...
My local network is pure IPv6, i cannot influence that in any way. I have a server within this network, which is connected to the network via a small local switch. Now i need to make this server accessible via a v4-address.

I got a solution once before with 6tunnel, but i have not been able to reproduce it, since i dont remember the exact commands, and whatever i try right now doesnt work.

My Setup:
3 devices:

• Server A, public IPv4 address available, way too weak for what i want to do, cant upgrade that.
• Server B, only IPv6 available, strong hardware, successfully doing what i need it to do, just not accessible from elsewhere.
• Laptop, used as "network slave", pretty weak but reliable.

What i did before was connect A via v6 to the laptop, and then via v4 to B in their shared local space.
I think i used some kind of -4/-6 additives in the command back when i set that up, but no matter which way i try, it doesnt work...

Any tipps/explanations?