We have a vSZ running with 3 interfaces behind a router.
Now we want to add a 2nd node to this cluster, also with 3 interfaces. This 2nd node is at a remote site and also behind a router. What ports should we forward in order to have te cluster interfaces to communicate?
It's a really bad idea, cluster doesn't work over Internet links. Don't even try! Even if you will be able to install it, you are guaranteed to have problems later, as Internet isn't stable enough.
This can be done only if you have 2 locations, which are not actually that remote, but say in the same city and connected by direct fiber link, preferred -- L2. Than cluster will work normally, same way, as when all nodes are located in one server room.