CCNA 1. Networking Basics v3.1.1 Student Lab Manual (796248), страница 23
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First thing that should be noted on the example computer isthat it is configured for Static addressing.5-7CCNA 1: Networking Basics v 3.1 - Lab 9.3.5Copyright 2003, Cisco Systems, Inc.Step 5 Enable DHCPTo enable DHCP, select Obtain an IP address automatically and typically select Obtain DNSserver address automatically.
The various settings will blank out as these options are selected. Ifthe computer had Static addressing and it needs to be restored, click on the Cancel button. To keepthe changed settings click OK.Older versions of Windows have multiple tabs and require selecting Obtain an IP addressautomatically on this tab and then going to the DNS Configuration tab to select Obtain DNSserver address automatically.If this computer was really being converted from static to DHCP, any entries in the Gateway andWINS Configuration tabs would need to be removed.If the computer had Static addressing and it needs to be restored, click on the Cancel button.To keep these settings click OK.6-7CCNA 1: Networking Basics v 3.1 - Lab 9.3.5Copyright 2003, Cisco Systems, Inc.Older versions of Windows will say that it is necessary to restart the computer. Windows 2000 andXP typically do not require a restart.Windows 95 might even ask for the installation CD-ROM to complete the process.If the computer was really being changed over to DHCP, Step 3 would be repeated to confirm thevalid set of configurations.ReflectionWhy might a network administrator prefer that various network profiles be used to hide the aboveoptions and screens, thereby preventing users from making any changes?_____________________________________________As a network administrator what would be some of the potential benefits of using a DHCP serverwithin a network?_____________________________________________________________________Note: Many small routers that are supplied for cable, DSL, or ISDN connections have DHCPconfigured by default.
This allows additional computers to share the network connectionthrough the use of a hub or switch. Each computer would need to be configured like in thelab. Typically, DHCP will assign addresses using one of the private networks, such as192.168.1.0, that are set-aside for this purpose. While it is common to allow these settings tobe changed, read and understand the instruction manual first.
Learn where the ResetDefaults button is located.7-7CCNA 1: Networking Basics v 3.1 - Lab 9.3.5Copyright 2003, Cisco Systems, Inc.Lab 9.3.7 Workstation ARPObjective•Introduce Address Resolution Protocol (ARP) and the arp –a workstation command.•Explore the arp command help feature using the -? option.Background / PreparationARP is used as a tool for confirming that a computer is successfully resolving network Layer 3addresses to Media Access Control (MAC) Layer 2 addresses. The TCP/IP network protocol relieson IP addresses like 192.168.14.211 to identify individual devices and to assist in navigating datapackets between networks.
While the IP address is essential to move data from one LAN to another,it cannot deliver the data in the destination LAN by itself. Local network protocols, like Ethernet orToken Ring, use the MAC, or Layer 2, address to identify local devices and deliver all data. Acomputer MAC address has been seen in prior labs.This is an example of a MAC address:•00-02-A5-9A-63-5CA MAC address is a 48-bit address displayed in Hexadecimal (HEX) format as six sets of two HEXcharacters separated by dashes. In this format each hex symbol represents 4 bits. With somedevices, the 12 hex characters may be displayed as three sets of four characters separated byperiods or colons (0002.A59A.635C).ARP maintains a table in the computer of IP and MAC address combinations. In other words, itkeeps track of which MAC address is associated with an IP address.
If ARP does not know the MACaddress of a local device, it issues a broadcast using the IP address. This broadcast searches for theMAC address that corresponds to the IP address. If the IP address is active on the LAN, it will send areply from which ARP will extract the MAC address. ARP will then add the address combination tothe local ARP table of the requesting computer.MAC addresses and therefore ARP are only used within the LAN. When a computer prepares apacket for transmission, it checks the destination IP address to see if it is part of the local network. Itdoes this by checking to see if the network portion of the IP address is the same as the localnetwork.
If it is, the ARP process is consulted to get the MAC address of the destination device usingthe IP address. The MAC address is then applied to the data packet and used for delivery.If the destination IP address is not local, the computer will need the MAC address of the defaultgateway. The default gateway is the router interface that the local network is connected to in order toprovide connectivity with other networks. The gateway MAC address is used because the packet willbe delivered there and the router will then forward it to the network it is intended for.If the computer does not receive any packets from an IP address after a few minutes, it will drop theMAC/IP entry from the ARP table assuming the device has logged off. Later attempts to access thatIP address will cause ARP to do another broadcast and update the table.This lab assumes the use of any version of Windows.
This is a non-destructive lab and can beperformed with a home machine without concern of changing the system configuration. Ideally, thislab will be done in a classroom or other LAN connected to the Internet. It can be done from a singleremote connection via a modem or DSL-type connection.1-4CCNA 1: Networking Basics v 3.1 - Lab 9.3.7Copyright 2003, Cisco Systems, Inc.Step 1 Establish a network connectionIf the connection to the Internet is dial-up, connect to the ISP to ensure that the computer has an IPaddress. In a TCP/IP LAN with a Dynamic Host Configuration Protocol (DHCP) server it should notbe necessary to do this step.Step 2 Access a command promptWindows NT / 2000 / XP users:Use the Start menu to open the Command Prompt window.
This window is similar to the MS-DOSwindow on older Windows versions:Start > Programs > Accessories > Command Prompt or Start > Programs > Command PromptWindows 95 / 98 / ME users:Use the Start menu to open the MS-DOS Prompt window:Start > Programs > Accessories > MS-DOS Prompt or Start > Programs > MS-DOS PromptStep 3 Display the ARP tablea.
In the window type arp -a and press Enter. Do not be surprised if there are no entries. Themessage displayed will probably be, ‘No ARP Entries Found’. Windows computers remove anyaddresses that are unused after a couple minutes.b. Try pinging a couple local addresses and a website URL. Then re-run the command. The figurebelow shows a possible result of the arp -a command. The MAC address for the website willbe listed because it is not local, but that will cause the default gateway to be listed. In theexample below 10.36.13.1 is the default gateway while the 10.36.13.92 and 10.36.13.101 areother network computers.
Notice that for each IP address there is a physical address, or MAC,and type, indicating how the address was learned.c.From the figure below, it might be logically concluded that the network is 10.36.13.0 and the hostcomputers are represented by 22, 1, 92, and 101.Step 4 Ping several URLsa.
Ping the following URLs and note the IP address of each. Also select one additional URL to pingand record it below:www.cisco.com: _____________________________www.msn.de: _____________________________________________: ____________________________b. Now run the arp –a command again and record the MAC addresses for each of the above nextto their IP addresses. Can it be done? ___________________________c.Why or why not? _____________________________________________________________________________________________________________________2-4CCNA 1: Networking Basics v 3.1 - Lab 9.3.7Copyright 2003, Cisco Systems, Inc.d.
What MAC address was used in delivering each of the pings to the URLs? _____________________________ Why? _____________________________________Step 4 Use the ARP help featureTry the command arp -? to see the help feature and look over the options.The purpose of this step is not so much the ARP command options but to demonstrate using the ? toaccess help, if available. Help is not always implemented uniformly. Some commands use /?instead of -?.Step 5 Use help with tracert and pingTry tracert -? and then ping -? to see the options available for the commands used previously.3-4CCNA 1: Networking Basics v 3.1 - Lab 9.3.7Copyright 2003, Cisco Systems, Inc.In looking at the help for ping, notice the –t option, which will send continuous pings, not just four.More importantly, notice the two commands to stop it:•Control-Break•Control-CThese two-key commands are common for stopping runaway activities. Try pinging a neighboringcomputer with the -t option and then try the Control-Break and Control-C features.
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