Networking All-in-One For Dummies. Doug LoweЧитать онлайн книгу.
important than technical skills. The network administrator needs to know how to do various maintenance tasks. Although this knowledge requires at least a little technical know-how, the organizational skills are more important.
Because network administration is such an important job, all the chapters in Book 9 is devoted to it.
Chapter 2
Network Infrastructure
IN THIS CHAPTER
In this chapter, I cover the key concepts of local area networks — that is, networks that are contained within a single location. Although this chapter may seem a little abstract, you’ll be much better prepared to design and implement a solid local area network if you have a good understanding of these concepts from the very beginning.
I go into more depth on many of the concepts presented in this chapter in Book 2, which dives deeper into the various networking standards and protocols.
Introducing Infrastructure
As I mention in the preceding chapter, a local area network (LAN) is a network that connects computers and other devices that are located in relatively close proximity to one another. Most LANs are contained to a single building, although it’s possible to create LANs that span several buildings at a single site, provided the buildings are close to one another. For the purposes of this chapter, I stick to LANs that operate within a single building and support anywhere from a few dozen to a few hundred users.
LANs exist to connect computing devices such as workstation computers, servers, printers, scanners, cameras, and so on, together. The essence of a network is the physical infrastructure that enables the connections. The infrastructure is similar to the infrastructure of a city. A city’s infrastructure has many physical elements, including roads, stop signs and stop lights, water supply lines, storm water drains, sewage lines and treatment plants, electrical distribution cables, transformers, and much more.
Similarly, the infrastructure of a network consists of physical elements:
Cables: These run through walls and ceiling spaces, through conduits, between floors, and wherever else they need to go to reach their destinations.
Patch panels: These allow cables to be organized at a central location.
Network switches: A switch is an intermediate device that sits between the networked devices that allows those devices to communicate with each other. In a real way, switches are the core of the network; without switches, computers wouldn’t be able to talk.
Wireless access points: A wireless access point (or WAP and sometimes just AP) lets devices connect wirelessly to the network. Depending on the size of your network and the physical space your users occupy, you may need more than one WAP. Each WAP needs to be connected to the LAN via a cabled switch connection.
At least one router: A router enables the network to the outside world. The most common use of a router is to connect the LAN to the Internet. However, routers can also be used to connect one LAN to another. I tell you more about routers in Chapter 3 of this minibook.
Understanding Network Protocols and Standards
To operate efficiently, the infrastructure of a network consists of devices that conform to well-known standards and protocols. A protocol provides a precise sequence of steps that each element of a network must follow to enable communications. Protocols also define the precise format of all data that is exchanged in a network. For example, the Internet Protocol (IP) defines the format of IP addresses: four eight-bit numbers called octets whose decimal values range from 0 to 255, as in 10.0.101.155.
A standard is a detailed definition of a protocol that has been established by a standards organization and that vendors follow when they create products. Without standards, it would be impossible for one vendor’s products to work with another vendor’s. Because of standards, you can instead purchase equipment from different vendors with the assurance that they’ll work together.
Network standards are organized into a framework called the Open Systems Interconnection (OSI) Reference Model. The OSI Reference Model establishes a hierarchy for protocols so that each protocol can deal with just one part of the overall task of data communications. The OSI Reference Model identifies seven distinct layers at which a protocol may operate:
Physical (layer 1): Describes the mechanical and electrical details of network components such as cables, connectors, and network interfaces.
Data link (layer 2): Describes the basic techniques that networks use to uniquely identify devices on the network (typically via a MAC address) and the means for one device to send information over the physical layer to another device, in the form of data packets. Switches operate at the data link layer, which means that they manage the efficient transmission of data packets from one device to another.
Network (layer 3): Handles the routing of data across networks. Routers operate at the network layer.
Transport (layer 4): Provides for reliable delivery of packets.
Session (layer 5): Establishes sessions between network applications.
Presentation (layer 6): Converts data so that systems that use different data formats can exchange information.
Application (layer 7): Allows applications to request network services.
Although the upper layers of the OSI model (layers 4 through 7) are equally important, in this chapter and the next, I focus on the first three layers of the OSI model — physical, data link, and network. These layers are the ones where the most common types of networking hardware such as cables, interfaces, switches, and routers operate.
Although