NAT Gateway
the address translatorA NAT gateway lets many private hosts share one public IP address. It rewrites the source address of outgoing packets, tracks each connection in a table, and maps the replies back to the right host — the reason your whole home shares one address.
A NAT gateway hides many private addresses behind one public IP and steers each reply back to its host.
How it works
+ remember
Each host’s private address and port are rewritten to the one public IP with a unique port. The gateway remembers the mapping, so when a reply arrives it knows exactly which host to hand it back to.
What a NAT gateway does, step by step
A host sends out a packet with its private source address.
The gateway swaps in the public IP and a fresh source port.
It stores private ↔ public in its translation table.
When the reply returns, it looks up the port and restores the private address.
In cybersecurity
NAT hides the internal network as a side effect — useful, but not a firewall on its own.
Outside hosts can’t address internal machines directly.
Add real filtering; NAT enforces no policy by itself.
Every port you open is a hole punched inward.
The state table is a target for exhaustion attacks.
Attribution needs port-level logs at scale.
Run NAT and a firewall together, never NAT alone.