This is to go through NAT, which are devices designed to work around the rarefaction of IPv4 addresses.

Firewalling is a different concept, but since you raise that issue of connectivity wrt. security, I have to say that what makes /me/ sad and anxious is to see how internet security has always been hinging on bloquing paquets based on the destination port.

Doing what's easy rather than what's correct, exemplified and labelled "professional solutions"...