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NAT

NAT. Network Address Translation. NAT Links. http://www.cisco.com/warp/public/556/nat-cisco.shtml http://www.howstuffworks.com/nat2.htm. Why?. 32-bit addresses Not all available (private, reserved, multicast, network/broadcast addresses, etc… ) Larger addresses (IPv6) will take time

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NAT

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  1. NAT Network Address Translation

  2. NAT Links • http://www.cisco.com/warp/public/556/nat-cisco.shtml • http://www.howstuffworks.com/nat2.htm

  3. Why? • 32-bit addresses • Not all available (private, reserved, multicast, network/broadcast addresses, etc… ) • Larger addresses (IPv6) will take time • Private addressing

  4. Topology

  5. NAT Modes • Classic: Private to Public IP translation • Overload: Multiple private to single public using different ports

  6. Classic • One to one correspondence between a private and a public IP address is established • Router keeps track of these in a table and translates back returning traffic

  7. Overload • All private addresses are translated into the same public address but different port numbers are used. • Table this time also contains the ports

  8. Additional Reasons to use NAT • Security: end IP addresses are not available => only connections initiated by inside are possible Exception: Static NAT (for servers) • Administration: migrating networks and multi-homes configurations are made easier

  9. Multi-homed example

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