Network Protocol Levels

You should be aware of the fact, that when talking about networking you will hear the word “protocol” all the time. This is because protocols are sets of standards that define all operations within a network. They define how various operations are to be performed. They may even define how devices outside the network can interact with the network. Protocols define everything from basic networking data structures, to higher level application programs. They define various services and utility programs. Protocols operate at many layers of the network models described below. There are protocols considered to be transport protocols such as TCP and UDP. Other protocols work at the network layer of the OSI network model shown below, and some protocols work at several of the network layers.

RFCs

The standards for TCP/IP are published in a series of documents called Requests for Comments (RFCs). RFCs describe the internal workings of the Internet. TCP/IP standards are always published as RFCs. Although RFCs define protocols not all RFCs define protocols but may define other requirements for the internet such as RFC 1543 which provides information about the preparation of RFCs. The following RFCs are very central to the TCP/IP protocol.

• RFC 1122 – Defines host requirements of the TCP/IP suite of protocols covering the link, network (IP), and transport (TCP, UDP) layers.
• RFC 1123 – The companion RFC to 1122 covering requirements for internet hosts at the application layer
• RFC 1812 – Defines requirements for internet gateways which are IPv4 Routers