3.5 NAT and PAT Explained
Key Concepts
- Network Address Translation (NAT)
- Port Address Translation (PAT)
- Static NAT
- Dynamic NAT
- Overloading (PAT)
Network Address Translation (NAT)
Network Address Translation (NAT) is a method used to modify IP address information in IP packet headers while they are in transit across a traffic routing device. NAT allows multiple devices on a local network to be mapped to a single public IP address, enabling them to communicate with the outside world.
Example: Think of NAT as a post office that changes the return address on a letter before sending it out. When a device on a private network sends data to the internet, the router changes the private IP address to a public IP address, allowing the data to be sent and received correctly.
Port Address Translation (PAT)
Port Address Translation (PAT), also known as NAT Overloading, is a type of NAT that allows multiple devices on a local network to share a single public IP address. PAT achieves this by using different port numbers for each device, ensuring that data packets are correctly routed back to the appropriate device.
Example: Consider PAT as a large office building where each employee has a unique office number (port) but shares the same street address (public IP). When a letter (data packet) arrives, the receptionist (router) uses the office number to deliver it to the correct employee.
Static NAT
Static NAT involves a one-to-one mapping between a private IP address and a public IP address. This type of NAT is commonly used for devices that need to be accessible from the internet, such as web servers.
Example: Imagine a VIP guest list at a party where each guest (private IP) has a specific seat (public IP). Static NAT ensures that each guest always sits in the same seat, making it easy for others to find them.
Dynamic NAT
Dynamic NAT involves mapping a private IP address to a public IP address from a pool of available public IP addresses. This type of NAT is used when there are more private IP addresses than public IP addresses available.
Example: Think of dynamic NAT as a hotel where guests (private IPs) are assigned rooms (public IPs) from a pool of available rooms. The room assignment changes each time a guest checks in, ensuring that all guests have a place to stay.
Overloading (PAT)
Overloading, or PAT, allows multiple private IP addresses to be translated to a single public IP address by using different port numbers. This is the most common form of NAT used in home and small business networks.
Example: Consider a busy restaurant where multiple customers (private IPs) share the same table (public IP) but are served by different waiters (ports). Each customer's order is correctly delivered to them based on the waiter's identification.