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NAT Types: Full Cone, Symmetric, and Hairpinning

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Not all NAT is the same

NAT translates private addresses to public, but how it handles incoming packets varies greatly. The four types differ in which external hosts can send packets back through an existing NAT mapping — from fully open (Full Cone) to per-destination (Symmetric).

This matters enormously for peer-to-peer applications: VoIP, video calls, gaming, WebRTC all need to establish direct connections between peers behind NATs.

Packets in motion — click to inspect:

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