Lecture Notes: Network Address Translation (NAT) and IPv4 Limitations

Introduction to IPv4 Limitations

20 billion+ devices on the internet.
IPv4 supports only 4.29 billion addresses.
IPv4 address space is exhausted; obtaining a new public IPv4 address is difficult.

NAT is used to increase the number of available devices using limited IP addresses.
Private IP addresses are used within local networks.

Defines specific private IP address ranges:
- 10.0.0.0 - 10.255.255.255
- 172.16.0.0 - 172.31.255.255
- 192.168.0.0 - 192.168.255.255
Devices within these ranges use private IP addresses (RFC 1918 IP addresses).

Translation of IP addresses occurs as devices communicate through the network.
Routers commonly perform this translation.

Private network: 10.10.20.0/24 (Example: Vala's device at 10.10.20.50).
Public IP address: Used for communication with an external server (e.g., professormesser.com at 104.20.19.63).
Translation Process:
- Vala sends a packet with source IP 10.10.20.50 to public IP 104.20.19.63.
- Router recognizes and translates private IP to a configured public IP.
- Destination server reverses the IP addresses for return communication.
- Router translates back to the internal private IP before sending to Vala.

Source Network Address Translation (Source NAT), NAT Overload, or Port Address Translation (PAT) used for multiple devices.

Port numbers are included in the IP address translation.
Example: Vala's device uses source port 3233 to communicate with port 80 on the server.
Router's Role:
- Changes both IP address and port number.
- Maintains a table mapping private IP and port to public IP and port.
- Example: Translates to public IP 94.1.1.1 with port 1055.
- Returns traffic by looking up the port and translating it back to the internal private IP and port.

Millions of NAT operations occur daily across routers on the internet.
Home and business routers commonly perform NAT overload or PAT for network communication.