Internetworking Overview :

NAT : " Network Address Translation "

Network Address Translation NAT can be used by companies when they run out of IP addresses to assign machines .The NAT process involves using private internal IP addresses and then translating those IP addresses to a valid IP addresses when leaving the LAN. To make the NAT schema possible three ranges of addresses have been declared as private addresses, companies may use them internally as they wish. The only rule is that no packet containing these addresses may appear on the Internet itself.

The three reserved ranges are:

10.0.0.0 (16,777,216 hosts) * many companies choice the first range.

172.16.0.0 (1,048,576 hosts)

192,168,0,0 (65,536 hosts)

NAT violate the architecture model of IP, that each IP address is associated with only one machine on the Internet. It can changes the Internet into a connection oriented network the NAT box maintains the state of the connection. Protocols at layer K make assumption about what protocols at layer K+1 have put in the payload –violating layer independence -.
NAT may fail if some protocols other than TCP or UDP are used, and if IP addresses are inserted into the payload data, then the NAT table will not translate that information and trouble could occur.



T.M.Harahsheh