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

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.

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

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

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.

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.