Internet Core Protocols: The Definitive Guide

The IP Standard

IP is defined in RFC 791, which has been republished as STD 5 (IP is an Internet Standard protocol). However, RFC 791 contained some vagaries that were clarified in RFC 1122 (Host Network Requirements). As such, IP implementations need to incorporate both RFC 791 and RFC 1122 in order to work reliably and consistently with other implementations.

RFC 791 begins by stating “The Internet Protocol is designed for use in interconnected systems of packet-switched computer communication networks. The Internet protocol provides for transmitting blocks of data called datagrams from sources to destinations. The Internet protocol also provides for fragmentation and reassembly of long datagrams, if necessary, for transmission through `small packet’ networks.”

RFC 791 goes on to say “The Internet Protocol is specifically limited in scope to provide the functions necessary to deliver a package of bits (an Internet datagram) from a source to a destination over an interconnected system of networks. There are no mechanisms to augment end-to-end data reliability, flow control, sequencing, or other services commonly found in host-to-host protocols.”

That pretty much sums it up. A source system will send a datagram to a destination system, either directly (if the destination host is on the local network) or by way of another system on the local network. If the physical medium that connects the sending and receiving systems offers enough capacity, IP will send all of the data in one ...