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Introduction to Network Address Translation (NAT)

CCNA: 0 to Hero - Comprehensive Network Engineering Bootcamp

Lesson 45: Introduction to Network Address Translation (NAT)

NAT is a fundamental process running on perimeter routers (or firewalls) that allows internal private IP addresses to communicate with external public networks (the Internet).

Key NAT Terminology

  • Inside Local (IL): The private address of the host inside the network (e.g., 192.168.1.10).
  • Inside Global (IG): The public address used by the host when communicating outside (the translated address).
  • Outside Local (OL): The internal address of a device outside your network (rarely used in basic scenarios).
  • Outside Global (OG): The public address of the destination server (e.g., 8.8.8.8).

Types of NAT

  1. Static NAT (One-to-One): Maps one private address to one public address. Used when a private server needs to be publicly accessible.
  2. Dynamic NAT (Many-to-Many): Maps a pool of private addresses to a pool of public addresses. Offers limited scale.
  3. PAT (Port Address Translation) / NAT Overload (Many-to-One): Maps many private addresses to a single public IP address by using unique source port numbers. This is the most common form of NAT used by homes and businesses.