NAT

Network Address Translation

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Why NAT

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NAT Terminology

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NAT : Network Address translation

• One-on-One relationship• internal (local) external (global)

• Only on Layer 3 – IP addresses• Static vs Dynamic

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The inside – outside – local – global mess

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Source NAT : Overview

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Static source NAT

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PAT Terminology

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PAT or “NAT overloading” - Overview

• Only outbound ! Unless static PAT

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Static PAT

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Problem 2 : Internal addresses also exist on outside

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Destination NAT

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NAT issues : IP address in the payload

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Examples of applications with addressing in the payload

• FTP• NetBIOS over TCP/IP• CuSeeMe• DNS • NetMeeting• Routing• SNMP

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Example : FTP

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Example : DNS and NAT