# What is Network Address Translation (NAT)?

> Network address translation (NAT) maps IP addresses from one address realm to another as packets cross a translating device.

- Canonical URL: https://yellowcube.eu/glossary/network-address-translation/
- Publisher: Yellow Cube
- Language: en
- Contact: hello@yellowcube.eu

## Content

In common IPv4 deployments, network address and port translation also maps transport ports, allowing multiple internal endpoints to share fewer externally routable addresses. Other NAT forms use static or dynamic one-to-one mappings.

For an outbound flow, the translator rewrites relevant packet-header fields, maintains a mapping, and reverses the translation for matching return traffic. Explicit inbound mappings can publish an internal service. NAT helps connect overlapping or private address realms and conserve IPv4 addresses, but it changes end-to-end addressing and can complicate protocols that carry addresses in their payloads.

### Key points

- **Translation state:** Define mapping behavior, timeouts, port allocation, inbound rules, logging, and capacity for the protocols the deployment must support.
- **Application impact:** Test peer-to-peer communication, embedded address data, IPsec modes, failover, and troubleshooting; some applications need traversal techniques or application-aware assistance.
- **Operational evidence:** Where attribution matters, preserve time-synchronized records that connect internal addresses and ports to external mappings without treating those records as proof of user identity.
- **Important limitation:** NAT is not a firewall, encryption mechanism, or authorization control. Many NAT products also filter unsolicited inbound packets, but filtering is separate from translation and does not replace explicit security policy.

### Related terms

[IP addressing: static and dynamic addresses](<https://yellowcube.eu/glossary/ip-addressing-static-and-dynamic-addresses/>) · [Firewall](<https://yellowcube.eu/glossary/firewall/>) · [Network access control list (ACL)](<https://yellowcube.eu/glossary/network-access-control-list/>) · [Network segmentation](<https://yellowcube.eu/glossary/network-segmentation/>) · [Virtual private network (VPN)](<https://yellowcube.eu/glossary/virtual-private-network/>)

### Sources

[RFC 2663: IP Network Address Translator Terminology and Considerations](https://www.rfc-editor.org/info/rfc2663) · [RFC 3022: Traditional IP Network Address Translator](https://www.rfc-editor.org/info/rfc3022) · [RFC 4787: Network Address Translation Behavioral Requirements for UDP](https://www.rfc-editor.org/info/rfc4787/)

## Attribution and scope

This Markdown representation is generated from the same approved content records as the canonical HTML page. Cite the canonical URL above when referencing this material. Product and service descriptions are informational; confirm project-specific requirements with Yellow Cube.