Network Address Translation (NAT) modifies IP addresses in packet headers as they pass through a router.
The basic operation:
Device on private network sends a packet
NAT router replaces private source IP with its public IP
Router forwards to the internet
Response comes back to the public IP
Router translates back to private IP and delivers
Where NAT runs:
- Home routers
- Enterprise firewalls
- Cloud load balancers
- Carrier networks (CGNAT)
NAT is invisible to end users.