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NAT and PAT

Updated Jan 16, 2018 ·

Network Address Translation (NAT)​

Network Address Translation (NAT) translates private IP addresses to a public IP address, allowing multiple devices on a local network to access the internet using a single public IP.

  • Conserves public IP addresses.
  • Hides internal network structure.
  • Provides a basic level of security.
  • Enables internal IP address management.
  • Supports dynamic and static NAT configurations.

Sample diagram:

Types of NAT​

  • Static NAT

    • Maps a single private IP address to a single public IP address.
    • Used for servers that need to be accessible from the internet.

  • Dynamic NAT

    • Maps a private IP address to a public IP from a pool of available IPs.
    • The pool of IP are available on a first-come, first-served basis
    • Used for general internet access.

Port Address Translation (PAT)​

Port Address Translation (PAT), a subset of NAT, maps multiple private IP addresses to a single public IP address using different ports, allowing multiple devices to share one public IP address simultaneously.

  • Can be a hardware or software configuration.
  • Normally enabled on the router, PAT hides the internal IPs.
  • Enables multiple connections from different devices.
  • Uses port numbers to differentiate traffic.
  • Supports large-scale networks with limited public IPs.
  • Often referred to as "NAT overload", or "NAT Gateway"

Almost similar to a forward proxy, but their differences are:

Feature / AspectPAT (Port Address Translation)Forward Proxy
OSI LayerLayer 4 (Transport)Layer 7 (Application)
CachingNoYes, can cache retrieved content
User AuthenticationNoCan require users to authenticate before fetching requests
FunctionTranslates multiple private IPs to a single public IP with portsActs on behalf of clients to fetch content from the internet

Sample diagram: