1. Network Address Translation Current problems with IP addresses:  Address depletion  Scaling in routing Solutions:  IPv6  CIDR  NAT

2. Network Address Translation What is NAT?  Informally, NAT is a method of connecting multiple computers on a local network to an external network using one IP address.  NAT can be incrementally deployed and only the local network routers need to be modified to implement NAT.  Backbone routers need not be modified.

3. Network Address Translation 198.76.29.7 10.33.96.5: 2000 …… Backbone router 198.76.28.4 … 10.81.13.22: 3000 … NAT Basic operation: Source -> 10.33.96.5: 2000 Destn. -> 198.76.28.4: 600 NAT 198.76.29.7 Source -> 198.76.29.7: 500 Destn. -> 198.76.28.4: 600 Source -> 198.76.28.4: 600 Destn. -> 198.76.29.7: 500 NAT 198.76.29.7 Source -> 198.76.28.4: 600 Destn. -> 10.33.96.5: 2000 Translation Reverse Translation

4. Network Address Translation Routing across NAT:  Local addresses are hidden from backbone.  Backbone-partitioned networks need special handling using tunneling. Header manipulations:  IP checksum should be changed.  For applications like FTP, application data should be modified which might require changing the TCP sequence no.s and acknowledgement no.s

5. Network Address Translation  ICMP messages need a lot of modifications when they pass through a NAT – two address modifications and three checksum modifications. Disadvantages:  NAT heavily violates the layering principle by looking into the transport and application layers.  Applications that contain IP address in their data cannot work through NAT unless NAT knows the exact occurrences.

6. Network Address Translation  NAT reduces the options for providing security because any application data that contains IP addresses cannot be encrypted.  NAT provides privacy by hiding the local addresses but this makes detecting of attacks like mail spam difficult. Conclusion: NAT has several negative characteristics but it could still act as a short-term solution to the address depletion and scaling problems.