CG-NAT

CG-NAT or Carrier-Grade NAT is a deployment of NAT that is done at the ISP scale, and it's extremely disliked among users as it completely breaks the ability to open ports or services at your home without utilizing a tunneling mechanism to an outside server. It's not significantly different from standard NAT except that it's done at the ISP level, adding further complexity and difficulty to making peer to peer connections.