1. NAT Network Address Translation

2. NAT Links http://www.cisco.com/warp/public/556/nat- cisco.shtmlhttp://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