CCNA Guide to Cisco Networking, Fourth EditionChapter 3 Solutions

Chapter 3 Solutions

Review Questions1. Which of the following is a reliable communications protocol?a. UDPb. TCPc. IPd. ICMP

2. Which of the following is used by the TFTP protocol?a. UDPb. TCPc. ICMPd. Telnet

3. Which of the following is a layer in the TCP/IP protocol stack? (Choose all that apply.)a. Applicationb. Presentationc. Physicald. Data Linke. Internetwork4. Which of the following is a TCP/IP Application layer protocol? (Choose all that apply.)a. DNSb. FTPc. UDPd. IPe. ICMP

5. Which of the following is a TCP/IP Internetwork layer protocol? (Choose all that apply.)a. ICMPb. FTPc. DNSd. ARPe. IP6. Which of the following is a TCP/IP Transport layer protocol? (Choose all that apply.)a. ARPb. RARPc. IPd. UDPe. TCP7. What are the Well-Known port numbers?a. 1024 - 49151b. 49152 - 65535c. 0 - 1021d. 1 - 10238. What is the purpose of the three-way handshake?a. to establish a reliable connection between two pointsb. to establish an unreliable connection between two pointsc. to establish a relationship at the Application layer between two pointsd. to establish a relationship at the Internetwork layer between two points

9. What is in an ARP table?a. destination and source MAC addressesb. MAC and corresponding IP addresses

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CCNA Guide to Cisco Networking, Fourth EditionChapter 3 Solutions

c. destination and source IP addressesd. routes to networks

10. What do computers do with the information in an ARP request when they are not the destination IP?

a. update their ARP caches with the destination informationb. update their ARP caches with the source informationc. update their routing tables with the ARP informationd. none of the above

11. Routers pass ARP broadcasts to find MAC addresses on other networks. True or False?

12. An ARP request is a ____________a. multicastb. unicastc. broadcastd. anycast

13. An ARP reply is a ________a. multicastb. unicastc. broadcastd. anycast

14. RARP has largely been replaced by ______________a. BOOTPb. ARPc. DHCPd. DNS

15. Ping and Trace both rely on what protocol?a. SMTPb. DNSc. ICMPd. TFTP

16. When sending packets to remote segments, routers rely on information in _____________ .a. ARP tablesb. routing tablesc. switching tablesd. ROM

17. Distance-vector algorithms and link-state algorithms are used in _____________________.a. DHCP b. ARPc. static routingd. dynamic routing18. All computers on the local segment process an ARP request at layer four of the OSI model.

True or False?

19. Each interface on a router represents an IP address on a different network. True or False?

20. The TCP acknowledgment process is ______________.a. expectationalb. sequentialc. exceptional

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CCNA Guide to Cisco Networking, Fourth EditionChapter 3 Solutions

d. sesquicentennial

21. Which of the following are NOT ICMP message types?a. Echo & destination unreachableb. Source quench & redirectc. Relay and rerouted. Parameter problem & informatione. Timestamp & time exceeded

22. Which layer of Cisco’s Three-Layer Hierarchical model provides services such as traffic control and security to the network?

a. Access layerb. Distribution layerc. Core layerd. all layers can provide these functionse. traffic control and security are not addressed by this model

Case ProjectsCase Project 1One: Resulted from a coordinated effort by the United States Department of Defense (DOD) in the late 1960sTwo: ARPA was charged with creating a wide area network (WAN). One of the results of the initial research was the TCP/IP protocol suite.Three: ARPA chose four university sites to help formulate the initial network: UCSB, UCLA, SRI, and the University of Utah. Initially, these sites were connected with 50-Kbps leased lines, which formed the Advanced Research Projects Agency Network. The name was later shortened to ARPANET.Four: Academic researchers found the network to be a great way to communicate with one another. Because the U.S. government never classified or restricted the technology used to create the network, researchers at other organizations used the information gained from the project to create their own TCP/IP networks. This furthered the development of the protocol stack as various groups developed more protocols for the TCP/IP suite.Five: The DOD funded two more related projects. The first was the adaptation of TCP/IP to work with the UNIX operating system. The second was the inclusion of the TCP/IP protocol with Berkeley UNIX (Berkeley Software Distribution UNIX [BSD UNIX]). At the time, 90% of the university science departments in the United States used BSD UNIX, so TCP/IP quickly increased in popularity and use.Six: Eventually, this network interconnected so many different organizations and sites that it became known as the Internet. Because taxpayer money funded the project and the government did not classify it, it was considered to be in the public domain. This opened the Internet to everyone, organizations and individuals alike.

Case Project 2The purpose of sliding windows is to provide flow control at layer 4 between communicating hosts when TCP is the transport protocol in use. It allows more than one packet to be sent at once to the receiving host. In essence, the source computer lets the destination computer know how many data packets it is willing to send before it requires an acknowledgement (ACK) that the data has been received. Large data transfers require large windows; otherwise, there would be a lot of additional network traffic generated by ACKs for each communication. Smaller networks that send small amounts of data can use smaller windows. Using large windows with small data transfers can force the sending computer to wait a disproportionate time for an ACK. It may then retransmit the data, which could result in getting an ACK for both the original, and the retransmitted data. Devices can dynamically adjust their window size.

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CCNA Guide to Cisco Networking, Fourth EditionChapter 3 Solutions

Case Project 3TCP/IP hosts examine frame headers of packets being transmitted on the network and learn which IP addresses are associated with which MAC addresses. They put these IP to MAC mappings in their ARP table in RAM. If a host wants to send data, it first must determine if the destination host is on the same network as it is. It does this by ANDING the IP addresses with their respective subnet masks. Next, the source puts its own IP and the destination's IP in the network layer header. At the data link layer both the source and destination MAC addresses are required. While the source computer knows its own MAC it may not know the destination's MAC. It looks in its ARP table for the correct mapping. If it is not there, the source host will send an ARP request which is a broadcast. All hosts on the local network (plus the router) will accept the broadcast at the data link layer, but only the host with the matching destination MAC address will answer with an ARP reply, which is a unicast frame. All hosts will use the ARP request information to update their ARP tables with the source IP and MAC information. Once it gets an ARP reply, the source host can send a unicast frame with the data correctly addressed to the destination. If the destination is determined not to be on the same network in the ANDING process, the source will send the frame to the default gateway. It will need an IP and MAC address for the default gateway and will ARP for the MAC address if necessary. Source hosts do not ARP for the final destination host if the destination host is determined to be on a different network. This is because broadcasts are not forwarded through a router and ARP requests are broadcasts.

Case Project 4Sometimes companies want to use diskless workstations rather than typical PCs that have hard drives in them. Usually, security is the reason for not using hard drives. Because IP configuration information is stored on hard drives, diskless workstations cannot retain this configuration information. Since a source host must have both an IP and MAC address to send data on a TCP/IP network, the diskless workstation must have some way to obtain its IP address. A device on the network can serve as a RARP server. A RARP server maintains a table with IP to MAC address mappings. When they boot, RARP clients broadcast a RARP request in order to obtain an IP address. The RARP server sends a RARP reply back to the client with the desired information. A workstation holds this IP information in RAM and it remains there until the workstation is shut off. Diskless workstations already know their MAC address because it is physically burned into the NIC card. The DHCP protocol is based on RARP but it is more sophisticated. RARP servers rely on a table of IP to MAC mappings so the given computer will always receive the same IP address. DHCP servers have a range of IP addresses they can assign to any host so a given computer may not always receive the same IP address. Also, DHCP can assign additional configuration parameters besides IP.

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