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Hairpin NAT

Hairpin NAT (NAT loopback) lets an internal host reach an internal service through its public address: the NAT "hairpins" the packet back to the internal destination instead of sending it out to the Internet.

Purpose

It removes the external detour when internal hosts access internal services by public domain/IP, improving efficiency and reachability.

Mechanism

An internal host sends to the public IP (which maps to an internal service); the NAT recognizes its own mapping, rewrites the destination to the internal service IP, and hairpins the packet, also rewriting the source to the NAT's internal IP (to avoid direct-return issues).

Use cases

  • Internal access via public domains
  • NAT loopback
  • Internal services reached through their public address

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References