RFC 1009 (rfc1009) - Page 2 of 55
Requirements for Internet gateways
Alternative Format: Original Text Document
RFC 1009 - Requirements for Internet Gateways June 1987 national supercomputer centers and other national scientific resources, and to provide a computer networking capability to a large number of universities and colleges. In this document there are many terms that may be obscure to one unfamiliar with the Internet protocols. There is not much to be done about that but to learn, so dive in. There are a few terms that are much abused in general discussion but are carefully and intentionally used in this document. These few terms are defined here. Packet A packet is the unit of transmission on a physical network. Datagram A datagram is the unit of transmission in the IP protocol. To cross a particular network a datagram is encapsulated inside a packet. Router A router is a switch that receives data transmission units from input interfaces and, depending on the addresses in those units, routes them to the appropriate output interfaces. There can be routers at different levels of protocol. For example, Interface Message Processors (IMPs) are packet-level routers. Gateway In the Internet documentation generally, and in this document specifically, a gateway is an IP-level router. In the Internet community the term has a long history of this usage [32]. 1.1. The DARPA Internet Architecture 1.1.1. Internet Protocols The Internet system consists of a number of interconnected packet networks supporting communication among host computers using the Internet protocols. These protocols include the Internet Protocol (IP), the Internet Control Message Protocol (ICMP), the Transmission Control Protocol (TCP), and application protocols depending upon them [22]. All Internet protocols use IP as the basic data transport mechanism. IP [1,31] is a datagram, or connectionless, internetwork service and includes provision for addressing, type-of-service specification, fragmentation and reassembly, and security information. ICMP [2] is considered an integral Braden & Postel
