Static NAT (Mapping Private IP 192.168.1.10 to Public IP 203.0.113.10)
Status: Traffic Routing -> NAT Translation Active on NAT Gateway Router.
Router Console - Gateway NAT Router (Router_A)
Router_A> enable
Router_A#
Router_A#
What is Network Address Translation (NAT)?
Network Address Translation (NAT) is a networking standard designed to conserve IPv4 space and secure internal LAN networks. It rewrites private IPv4 address headers (RFC 1918) into routable public IPv4 addresses as packets cross from an inside private boundary to an outside public internet boundary.
The 4 Core Address Terminology Definitions
Inside Local: The private IP address assigned to a host on the internal private LAN (e.g., 192.168.1.10).
Inside Global: The public IP address assigned by the NAT router representing the internal host to the outside internet (e.g., 203.0.113.10).
Outside Local: The IP address of an outside host as known to internal LAN devices (typically identical to Outside Global).
Outside Global: The actual public IP address assigned to the destination host on the internet or public cloud (e.g., 8.8.8.8 or 198.51.100.50).
Types of Network Address Translation
Static NAT (1-to-1): Maps a single private Inside Local IP to a single public Inside Global IP permanently. Used primarily for web/mail servers hosted internally that require public internet access.
Dynamic NAT (Many-to-Many): Dynamically maps private Inside Local IPs to an available pool of public Inside Global IPs on a first-come, first-served basis.
PAT / NAT Overload (Many-to-1): Maps multiple private Inside Local IPs to a single public IP using unique TCP/UDP **Port Numbers** (Layer 4) to track active connections. This is the standard NAT model used in home and enterprise internet connections.
NAT Topology Pathway
Client PC (Inside Local) $\rightarrow$ NAT Gateway Router (Translation Boundary) $\rightarrow$ ISP Router $\rightarrow$ Internet Cloud $\rightarrow$ Target Web Server (Outside Global)