Indonesia has wide air space with many aircrafts flies every day. In order to manage its air traffic effectively and efficiently, Indonesia must have and utilize the Communication Navigation Surveillance- Air Traffic Management system. The system includes communication, navigation and surveillance systems and it uses digital technologies to support the air traffic management system. For the communication system, an Aeronautical Telecommunication Network (ATN) is used to provide the digital data link to supplement the voice communication. In ATN, the core of the protocol is Connectionless Network Protocol (CLNP). It is located in the network layer of OSI layer. This book show how to implement the forwarding Protocol Data Unit (PDU) function in the routing process and to compose the Request Address PDU and Assign Address PDU for routing exchange protocol between End System and Intermediate System. The research is implemented based on designed CLNP that refers to the ISO 8473 and Internet Protocol design using Linux kernel 2.6.x. This book should help the researchers or the readers who are interested in the networking and aeronautical field.