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NAT Diagnostics

NAT Diagnostics. Derek MacDonald. Overview. NAT type discovery was defined in 3489 Was not included in 3489bis as the discovery mechanism is not accurate A reduced mechanism may be useful as a diagnostic tool Could be useful to optimize P2P applications. Problems from 3489.

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NAT Diagnostics

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  1. NAT Diagnostics Derek MacDonald

  2. Overview • NAT type discovery was defined in 3489 • Was not included in 3489bis as the discovery mechanism is not accurate • A reduced mechanism may be useful as a diagnostic tool • Could be useful to optimize P2P applications

  3. Problems from 3489 • NAT behavior is not stable; NAT devices often get “worse” and change behavior under load or with time • Many corporate NAT/firewalls devices can become address and port dependent(mapping & filtering) • Consumer NATs seem to be stable • NAT binding timeouts are not stable

  4. Utility for SIP endpoints • Can be used to detect if the NAT type requires a relay solution • Risky, as NAT type may change • Ice will move traffic off relay server • May save relay cost when communicating with non-ICE endpoints but will incur a risk that RTP traffic may stop flowing

  5. Hairpinning • Detecting whether or not a NAT supports hairpinning seems to work • Could be used by endpoints to advertise a relay solution in the c line rather than th detected external IP address to give a better chance of connectivity • Not needed when ICE is supported

  6. P2P Applications • P2P applications are interested in three NAT conditions: • Not behind a NAT/Endpoint Independent NAT(“supernode candidate”) • Address independent mapping & Address restricted filtering(keep-alives to all active peers) • Address dependent mapping & filtering • P2P applications would need to periodically rediscover

  7. Port Dependent Filtering & P2P • Linux issues • Port preserving when same ports are used • Port dependent filtering NATs can not reach PDMADF NATs even with ICE; however elements behind an evil PDMADF must acquire relay to participate in the network

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