CHAPTER 2

Communicating over the Network

The Study Guide portion of this chapter uses a combination of multiple-choice, matching, fill-in-the-blank, and open-ended questions to test your knowledge of how devices communicate over the network.

The Labs and Activities portion of this chapter includes all the online curriculum activities and labs to further reinforce that you have mastered the practical, hands-on skills needed to use some critical tools to help evaluate network communications.

As you work through this chapter, use Chapter 2 in the Network Fundamentals CCNA Exploration online curriculum or use the corresponding Chapter 2 in the Networking Fundamentals, CCNA Exploration Companion Guide, for assistance.

Study Guide

The Platform for Communications

Communication begins with a message, or information, that must be sent from one individual or device to another. People exchange ideas using many different communication methods. All of these methods have three elements in common.

Concept Questions

1.What are the three elements of communication?

  1. What is the process of breaking large messages, or flow of data, into smaller, easier-to-manage pieces

called?

S

  1. What is the process used to allow many different conversations to be interleaved on a network called? M
  2. Modern networks primarily use three types of media to interconnect devices. What are these three

types?

W

F

W

Vocabulary Exercise: Matching

In Table 2-1, match the definition on the right with a term on the left.

Table 2-1Components of the Network

TermDefinition

  1. Devices____. Cat5 cable, wireless connection, fiber-optic cable
  2. Media____. Computer, switch, router
  3. Services____. E-mail, web browser

In Table 2-2, identify the definition on the left with either end devices or intermediary devices on the right.

Table 2-2End or Intermediary Device

DefinitionDevice Type

Computers (work stations, laptops, file servers, web servers) devices

Mobile handheld devices (such as wireless barcode scanners, PDAs) devices

Network access devices (hubs, switches, and wireless access points) device

Network printers devices

Internetworking devices (routers) device

VoIP phones devices

Communication servers and modems device

Security cameras devices

Security devices (firewalls) device

LANs, WANs, and Internetworks

Network infrastructures can vary greatly in terms of the following:

The size of the area covered

The number of users connected

The number and types of services available

This section tests your knowledge of the differences between LANs, WANs, and internetworks.

Vocabulary Exercise: Completion

Fill in the blanks for the following statements.

1. The term I is often used to refer to a private connection of LANs and WANs that belongs to an organization, and is designed to be accessible only by the organization’s members, employees, or others with authorization.

  1. A L is usually administered by a single organization.
  2. W use specifically designed network devices to make the interconnections between L .
  3. The media connecting the PC to the networking device plugs directly into the N .

Vocabulary Exercise: Matching

In Table 2-3, match the definition on the right with a term on the left.

Table 2-3LANs, WANs, and Internetworks

TermDefinition

  1. LANs____. When a company or organization has locations that are separated by large geographic distances, it might be necessary to use a telecommunications service provider (TSP) to interconnect the LANs at the different locations.
  2. WANs_____. An individual network usually spans a single geographic area, providing services and applications to people within a common organizational structure, such as a single business, campus, or region.
  3. Internetworks_____. A global mesh of interconnected networks.

In Table 2-4, match the term on the left with the correct symbol number from Figure 2-1.

Table 2-4LANs, WANs, and Internetworks
Device / Number
Router
Firewall
Wireless access point
LAN hub
LAN switch
IP phone
Wireless router
Wireless media
Server
Laptop
LAN media
Desktop computer
WAN media

Figure 2-1 Common Data Network Symbols

Protocols

All communication, whether face to face or over a network, is governed by predetermined rules called protocols. These protocols are specific to the characteristics of the conversation.

Vocabulary Exercise: Completion

Fill in the blanks for the following statements.

  1. Successful communication between hosts on a network requires the interaction of many different protocols. A group of interrelated protocols that are necessary to perform a communication function is called a p .
  2. All communication, whether face to face or over a network, is governed by predetermined rules called p .
  3. A s is a process or protocol that has been endorsed by the networking industry and ratified by a standards organization.
  4. The most common internetwork protocol is I .

Concept Questions

1. What processes do networking protocol suites describe?

2. What are some benefits to using a layered model to describe network protocols and operations?

Using Layered Models

To visualize the interaction between various protocols, it is common to use a layered model. A layered model depicts the operation of the protocols occurring within each layer, and the interaction with the layers above and below it.

Vocabulary Exercise: Matching

In Table 2-5, match the definition on the right with a term on the left.

Table 2-5 TCP/IP Model

TermDefinition

  1. Application layer___. Uses packet sequencing and application mapping through port numbers
  1. Transport layer___. Represents data to the user plus encoding and dialog control
  2. Internet layer____. Controls the hardware devices and media that make up the network
  1. Network access layer _____. Determines the best path through the network

In Table 2-6, match the definition on the right with a term on the left.

Table 2-6OSI Model

TermDefinition

  1. Application layer___. Protocols describe methods for exchanging data frames between devices over a common media.
  2. Presentation layer___. Provides the means for end-to-end connectivity between individuals in the human network using data networks.
  3. Session layer____. Describes the mechanical, electrical, functional, and procedural means to activate, maintain, and deactivate physical connections for bit transmission to and from a network device.
  4. Transport layer ____. Provides services to the presentation layer to organize its dialogue and to manage data exchange. Ensures that loss of connection can be recovered and reset if data flow is interrupted before all data is received.
  5. Network layer____. Provides for common representation of the data transferred between application layer services.

Table 2-6OSI Model continued

TermDefinition

  1. Data link layer___. Provides connectivity services that route packets from source network to destination network.
  2. Physical layer___. Defines services to segment, transfer, and reassemble the data for individual communications between the end devices.

Network Addressing

Various types of addresses must be included in a packet to successfully deliver the data from a source application running on one host to the correct destination application running on another. Using the OSI model as a guide, you can see the different addresses and identifiers that are necessary at each layer.

Vocabulary Exercise: Completion

Fill in the blanks for the following statements.

  1. The first identifier, the host physical address, is contained in the header of the Layer 2 protocol data unit (PDU), called a f .Layer 2 is concerned with the delivery of messages on a single local network. The Layer 2 address is unique on the local network and represents the address of the end device on the physical media. In a LAN using Ethernet, this address is called the M _ )address.
  2. A unique dialogue between devices is identified with a pair of Layer 4 source and destination p______that are representative of the two communicating applications.

Multiple-Choice Questions

Choose the best answer for each of the questions that follow.

  1. What kind of protocols are primarily designed to move data from one local network to another local network within an internetwork?
  1. Layer 1
  2. Layer 2
  3. Layer 3
  4. Layer 4
  1. Which devices make Layer 3 decisions?
  1. Routers
  2. Switches
  3. Hubs
  4. Servers

Labs and Activities

Activity 2-1: Using NeoTrace to View Internetworks (2.2.5.1)

Upon completion of this activity, you will be able to do the following:

Explain the use of route tracing programs, such as tracert and NeoTrace.

Use tracert and NeoTrace to trace a route from its PC to a distant server.

Describe the interconnected and global nature of the Internet with respect to data flow.

Background

Route-tracing software is a utility that lists the networks data has to traverse from the user’s originating device to a distant destination network device.

This network tool is typically executed in UNIX and similar systems at the command line as follows:

traceroute destination network name or end device address

This network tool is typically executed in Microsoft Windows systems at the command line as follows:

tracert destination network name or end device address

This tool determines the route taken by packets across an IP network.

The traceroute (or tracert) tool is often used for network troubleshooting. By showing a list of routers traversed, it enables the user to identify the path taken to reach a particular destination on the network or across internetworks. Each router represents a point where one network connects to another network and the packet was forwarded through. The number of routers is known as the number of “hops” the data traveled from source to destination.

The displayed list can help identify data-flow problems when trying to access a service such as a web-site. It can also be useful when performing tasks such as downloading data. If multiple websites (mirrors) are available for the same file of data, one can trace each mirror to get a good idea of which mirror would be the fastest to use.

Note, however, that because of the “meshed” nature of the interconnected networks that make up the Internet and IP’s capability to select different pathways over which to send packets, two trace routes between the same source and destination conducted some time apart might produce different results.

Tools such as traceroute/tracert are usually embedded within the operating system of the end device.

Others such as NeoTrace are proprietary programs that provide extra information. NeoTrace uses available online information to graphically display the route traced on a global map, for example.

Scenario

Using an Internet connection, you use two route-tracing programs to examine the Internet pathway to destination networks.

You should perform this activity on a computer that has Internet access and access to a command line. First, you use the Windows embedded tracert utility, and then the more enhanced NeoTrace program. This lab assumes the installation of NeoTrace. Remember, some computers running Windows XP might have firewall programs enabled that might prevent tracert and NeoTrace from operating; you might have to turn your firewalls off for this lab.

Task 1: Trace Route to Remote Server

Step 1.Trace the route to a distant network.

To trace the route to a distant network, the PC being used must have a working connection to the class/lab network.

Step 2. At the command-line prompt, enter tracert .

The first output line should show the fully qualified domain name (FQDN) followed by the IP address. The lab Domain Name Service (DNS) server was able to resolve the name to an IP address. Without this name resolution, the tracert would have failed, because this tool operates at the TCP/IP layers, which understand valid IP addresses only.

If DNS is not available, the IP address of the destination device rather than the server name has to be entered after the tracert command.

Step 3. Examine the output displayed.

How many hops between the source and destination? Answer varies based on location

Example 2-1 shows the successful result when running tracert from a location in Bavaria, Germany.

Example 2-1tracert Output

The first output line shows the FQDN, followed by the IP address. Therefore, a DNS server was able to resolve the name to an IP address. Then, there are listings of all routers through which the tracert requests had to pass to get to the destination.

Step 4. Try the same trace route on a PC connected to the Internet and examine your output: Number of hops to Answer varies based on location

Step 5. Try another trace route on the same PC, and examine your output.

Destination URL: Answer varies based on URL

Destination IP address: Answer varies based on URL

Task 2: Trace Route Using NeoTrace

Step 1. Launch the NeoTrace program.

Step 2. On the View menu, choose Options. Click the Map tab, and in the Home Location section click the Set Home Location button.

Step 3. Follow the instructions to select your country and location within your country.

Alternatively, you can click the Advanced button, which enables you to enter the precise latitude and longitude of your location.

Step 4. Enter in the Target field and click Go.

Step 5. From the View menu, List View displays the list of routers similar to tracert.

Node View from the View menu displays the connections graphically with symbols.

Map View from the View menu displays the links and routers in their geographic location on a global map.

Step 6.Select each view in turn and note the differences and similarities.

Step 7. Try a number of different URLs and view the routes to those destinations.

Task 3: Reflection

Review the purpose and usefulness of route-tracing programs.

Relate the displays of the output of NeoTrace to the concept of interconnected networks and the glob-al nature of the Internet.

Task 4: Challenge

Consider and discuss possible network security issues that could arise from the use of programs such as traceroute and NeoTrace. Consider which technical details are revealed and how this information could perhaps be misused.

Task 5: Clean Up

Exit the NeoTrace program. Unless instructed otherwise by your instructor, properly shut down the computer.

Lab 2-1: Topology Orientation and Building a Small Network (2.6.1.1)

Upon completion of this lab, you will be able to do the following:

Correctly identify cables for use in the network.

Physically cable a peer-to-peer and switched network.

Verify basic connectivity on each network.

Background

Many network problems can be fixed at the physical layer of a network. Therefore, you need to under-stand clearly which cables to use for your network connections.

At the physical layer (Layer 1) of the OSI model, end devices must be connected by media (cables). The type of media required depends on the type of device being connected. In the basic portion of this lab, you use straight-through or patch cables to connect workstations and switches.

In addition, two or more devices communicate through an address. The network layer (Layer 3) requires a unique address (also known as a logical address or IP address), which allows the data to reach the appropriate destination device.

Addressing for this lab is applied to the workstations and is used to enable communication between the devices.

Scenario

This lab starts with the simplest form of networking (peer to peer) and ends with the lab connecting through a switch, as shown in Figure 2-2.

Figure 2-2 Topology for Lab 2-1

Peer-to-Peer Network

Task 1: Create a Peer-to-Peer Network

Step 1.Select a lab partner.

Step 2. Obtain the following equipment and resources for the lab:

Two workstations

Two straight-through (patch) cables

One crossover cable

One switch (or hub)

Task 2: Identify the Cables Used in a Network

Before the devices can be cabled, you must identify the types of media you intend to use. The cables used in this lab are crossover and straight-through.

Use a crossover cable to connect two workstations to each other through their network interface card (NIC) Ethernet port. This is an Ethernet cable. Notice when you look at the plug that the orange and green wires are in opposite positions on each end of the cable.

Use a straight-through cable to connect the router’s Ethernet port to a switch port or a workstation to a switch port. This is also an Ethernet cable. Notice when you look at the plug that both ends of the cable are exactly the same in each pin position.

Task 3: Cable the Peer-to-Peer Network

Step 1. Connect two workstations.

Using the correct Ethernet cable, connect two workstations together, as shown in Figure 2-3. Connect one end of the cable to the NIC port on PC1 and the other end of the cable to PC2.

Figure 2-3 Peer-to-Peer Cabling

Which cable did you use? Crossover cable

Step 2. Apply a Layer 3 address to the workstations.

To complete this task, use the following step-by-step instructions.

Note: These steps must be completed on each workstation. The instructions are for Windows XP. Steps may differ slightly if you are using a different operating system.

a. On your computer, click Start, right-click My Network Places, and then click Properties. The Network Connections window should appear, with icons showing the different network connections. See Figure 2-4.