NAT

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NAT

• Network Address Translation

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NAT Links

• http//www.cisco.com/warp/public/556/nat-cisco.sht
  ml
• http//www.howstuffworks.com/nat2.htm

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Why?

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

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Topology
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NAT Modes

• Classic Private to Public IP translation
• Overload Multiple private to single public using
  different ports

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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

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Overload

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

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Additional Reasons to use NAT

• Security end IP addresses are not available gt
  only connections initiated by inside are possible
• Exception Static NAT (for servers)
• Administration migrating networks and
  multi-homes configurations are made easier

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Multi-homed example