[Network] Type of NAT (Network Address Translation)

04 type of NAT:

1. Full-cone NAT, also known as one-to-one NAT (NAT Toàn vành):

• Once an internal address (iAddr:iPort) is mapped to an external address (eAddr:ePort), any packets from iAddr:iPort are sent through eAddr:ePort.
• Any external host can send packets to iAddr:iPort by sending packets to eAddr:ePort.

2. (Address)-restricted-cone NAT (NAT Giới hạn địa chỉ)

• Once an internal address (iAddr:iPort) is mapped to an external address (eAddr:ePort), any packets from iAddr:iPort are sent through eAddr:ePort.
• An external host (hAddr:any) can send packets to iAddr:iPort by sending packets to eAddr:ePort only if iAddr:iPort has previously sent a packet to hAddr:any. "Any" means the port number doesn't matter.

3. Port-restricted cone NAT (NAT Giới hạn Cổng)

Like an address restricted cone NAT, but the restriction includes port numbers.

• Once an internal address (iAddr:iPort) is mapped to an external address (eAddr:ePort), any packets from iAddr:iPort are sent through eAddr:ePort.
• An external host (hAddr:hPort) can send packets to iAddr:iPort by sending packets to eAddr:ePort only if iAddr:iPort has previously sent a packet to hAddr:hPort.

4. Symmetric NAT (NAT Đối xứng)

• Each request from the same internal IP address and port to a specific destination IP address and port is mapped to a unique external source IP address and port; if the same internal host sends a packet even with the same source address and port but to a different destination, a different mapping is used.
• Only an external host that receives a packet from an internal host can send a packet back.