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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)

NFS File System Model and the Mount Protocol 1 Host Configuration and TCP/IP Host Configuration Protocols (BOOTP and DHCP)

Some folks study the OSI Reference Model just to pass a test and otherwise consider it “useless”. I think it's important because it shows how the different hardware and software components of an internetwork fit together. One aspect of this is that the model lets us see clearly how the functions of networks are implemented by building the higher-layer ones upon those at lower layers. We start at the bottom layers dealing primarily with hardware, and build upon them the software and protocols that make networks and internetworks in the middle layers. The highest layers of the OSI model, especially the application layer, run on top of the internetwork implemented by the layers below. It is therefore at this level that we normally talk about the protocols and applications that permit end users to perform different network communication tasks.

Of course, the users are why we create networks and internetworks in the first place. But while the application layer is indeed where we find user-oriented protocols, users are not the only ones who need to make use of network applications at this level. Network administrators have a number of functions that they must perform on a daily basis to keep networks running smoothly and efficiently, and many of these use support protocols at higher layers.

Decades ago, an administrator was probably responsible for only a small number of computers, all in the same building or even the same room. When something in the network needed to be fixed or changed, the techie would walk over to it and “administer” it. Today, a company's computers are probably not close at hand; they are likely spread out across a campus, a country or the entire world. It is no longer feasible to travel to each computer to perform various maintenance tasks. And with larger networks, trying to manually maintain thousands of computers, even if they were in the same building, would not be possible.

To make administration practical on modern networks, special application-level protocols were created that allow administrators to work with distance devices in a more automated manner over the internetwork itself. It may seem ironic to be using the internetwork to help administer the internetwork, but many tasks such as device configuration and management can be performed effectively using software protocols. Using these protocols yields significant advantages over manual processes, and is part of what keeps the internetworks we rely on running smoothly.

This section takes a look at two classes of administrative tasks that are served by application-layer protocols. The first subsection deals with host configuration, describing the concepts behind the process, and two protocols used for accomplishing automated configuration of internetwork hosts. The second describes protocols used to remotely manage, monitor and control remote hardware devices on an internetwork.

As part of this discussion, I describe in detail four TCP/IP protocols that implement host configuration and management functions. These are the TCP/IP Boot Protocol (BOOTP) and Dynamic Host Configuration Protocol (DHCP) for host configuration, and the Simple Network Management Protocol (SNMP) and Remote Network Monitoring Protocol (RMON) for network management.

NFS File System Model and the Mount Protocol 1 Host Configuration and TCP/IP Host Configuration Protocols (BOOTP and DHCP)