Chapter 1

Looking at the Cisco Network World

IN THIS CHAPTER

Meeting the OSI model (It's mostly harmless.)

Working with switches, routers, and firewalls

Going wireless

Getting your network voice

Checking out the Cisco product lines

If you are reading this book, you likely either have a network that is made up of Cisco networking products or you want to introduce the Cisco network products into your network. Although this book focuses its attention on Cisco products, you do not have to have Cisco network devices on your network to receive a benefit from reading this book. Although you examine many features that are specific to Cisco products, you also gain a wide range of networking knowledge that applies to all networking hardware, regardless of the vendor.

This chapter performs a quick overview of all the devices that exist on your network, allowing your computers, servers, and other user-related network devices to communicate with each other. I start with the network devices that your computer connects to and move further into the depths of the network from there, through routers and firewalls, and then through wireless and network-connected phone hardware. After you read about these general hardware devices, you receive an overview of the classes of Cisco networking devices, such as enterprise, small business, and home devices.

After you read this chapter, you will have a rough grasp of network devices and how they all fit together on the network and an idea of the type of products that Cisco networking involves.

The rest of this book looks at most of these products and shows you how to configure, manage, and support them. Although some Home products are in this mix, I spend most of the time showing you the products you use on your office network (be it small or large).

Although I do cover the whole network model in this chapter, I do not go very deep on the individual layers. If you want detailed knowledge of the ins and outs of these devices operating at different layers of the network model, you may want to review Book 1, Chapter 4.

Glazing Over the OSI Network Layer Model

Well, much as I hate to do this to you so early (mwa ha ha ha), before I discuss the actual devices, you need to understand how the standards-setter in the networking industry, the International Organization for Standardization (ISO), defines how network devices should be designed to communicate with each other. The ISO has proposed a network model that allows for this communication to take place, and although this is good from a theoretical level, it is not always followed, especially since it was published after many networking protocols and methods had been created.

The network model that I describe is the Open System Interconnection (OSI) model, which has seven layers and defines what types of activities should be conducted at each layer. Figure 1-1 shows the seven layers graphically.

FIGURE 1-1: The OSI network model.

The order of the layers, as they are defined, go from the physical components at the lowest layer (which are used to attach a computer to the network) up to applications at the highest layer that are used on that computer. Some people find that it makes sense to be introduced to the layers in this bottom-up order; while others find the reverse or top-down order is easier to follow. I introduce the layers in the top-down order (highest to lowest as you follow Figure 1-1 from top to bottom), so if you find it confusing, read them from the bottom to the top. The seven layers are

• Layer 7 - Application: The role of the application layer in the OSI model is to interface with you on your computer or data on a server. For example, if you want to load a page of data from a website, your web browser uses the Hypertext Transport Protocol (HTTP) application layer protocol. To develop a new web browser or web server software, you need only to understand that one application layer protocol. Your HTTP data request travels down through the layers on your computer, over the data network, and up through the network layers on the server, which retrieves the Hypertext Markup Language (HTML) file and returns it to your computer in the same manner.
• Layer 6 - Presentation: The presentation layer is responsible for data formatting. This may be character formatting, such as ASCII or Unicode data formats, or compression and data encryption. Think of the presentation layer as the formatting layer in the OSI model. For example, many web servers can compress data that is sent to the web browsers. This compression is the presentation layer component, and it needs to be understood by the presentation layer on the receiving computers.

• Layer 5 - Session: The session layer establishes a communication dialogue between the two participants in the communication process; that is, two computers over a network. After you have a piece of data that is formatted properly, the session layer ensures that it is ready to be sent over the network. Video conference connections between devices make use of sessions, as do Remote Procedure Calls (RPC).

  For example, if the OSI model was used by the post office, the application layer identifies the data on a sheet of paper, the presentation layer defines that the paper must be in an envelope, and the session layer defines that the envelope must have a properly formatted address on it - including a name, street number, street name, city, state, and zip code - and preferably, a return address as well.

• Layer 4 - Transport: The transport layer defines what type of checks may be performed to validate the data's delivery as either reliable or unreliable. Reliable delivery ensures that the data packets get to where they are supposed to go and that they arrive in the same order they were sent. Unreliable delivery does not guarantee that the data packets arrive in any specific order, and in fact, does not even ensure that the data packets arrives where it is supposed to go, at all.

  Staying with the post office example, reliable delivery allows you to request a signature of the recipient and get a tracking number, whereas unreliable delivery just gives you a stamp and a post office box. Although most unreliable delivery does arrive where it is supposed to, you are never really sure whether it has, until you somehow confirm with the other party.

  On your data network, some data is sent unreliably, such as a request for an Internet Protocol (IP) address from a network server. Other data is sent reliably, such as saving a file to a server.

• Layer 3 - Network: The network layer uses logical address and routing. Logical address applies an address that means something to the communication protocol that you are using, such as an Internet Protocol (IP) address, but may not mean anything to the physical delivery process, which makes use of a Layer 2 address. Routing the data delivers it to the required destination, which may be nearby or very far away. The network layer also splits large pieces of data into smaller pieces for delivery.

  To continue the post office example from the Layer 5 discussion, you had to provide a properly formatted address to get your letter to a building or office for delivery by the postal service. Each part of the address has a zone (or place) where it is used, such as the zip code used by the postal sorting and routing department; the street address used by the mail carrier; and the name by people at the destination address. Depending on how mail delivery starts in your organization, some of this required information for the address may have originally been missing from the envelope. The mail delivery process may have started by dropping a letter addressed to John Smith, New York Office in your desk's outbox. That letter is picked up by your mail clerk who appended John's office number and the street address of the New York office. He then delivered (or routed) it to the postal service or courier company.

  On your data network, this logical address is likely your IP address, which is used as a unique identifier on the internet to determine the endpoint for communication. IP routing moves the data through a series of interconnected networks until the data arrives at the targeted computer or device.

• Layer 2 - Data Link: The data link layer assigns or makes use of physical addressing as well as controlling access to the physical medium. If you are dealing with standard Ethernet network cards, the manufacturer assigns a globally unique address to each card. This address is the Media Access Control (MAC)address, and it is used at that data link layer to establish communication between two locally attached devices.

  The data link layer also controls how the data is interchanged between these two locally attached devices or network cards. Think of this layer as a physical language or a set of communication processes. When dealing with your network, two of the main communication processes would be either Carrier Sense Multiple Access with Collision Detection (CSMA/CD) or Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). In the case of standard Ethernet networks, CSMA/CD is used, while CSMA/CA is used for AppleTalk and most 802.11 wireless networks. With this defined, the data link layer formats a stream of zeros and ones...