Networking I Name: Fall 1997 Final Exam w/ answers (ID): Short Answer (2 pts each): 1. IEEE 802.3 and ethernet are very similar types of networks in that they both use CSMA/CD. Describe the functionality of CSMA/CD. Nodes on the network are able to sense if another node is transmitting. If no one else is talking, the node will send its transmission. Nodes are also able to detect a "collision," which occurs when two (or more) nodes transmit at the same time. When this happens, each transmitter waits a random period of time before restarting the process (see if someone is transmitting, then transmit when all is clear). 2. IEEE 802.3 and ethernet differ slightly in what way? Although IEEE 802.3 and ethernet both use the same frame size and CSMA/CD for data transmission, IEEE 802.3 (which was defined after ethernet had been in existence for a number of years) includes more header information within the frame. This means that the space available for the data payload is smaller in an 802.3 frame than in an ethernet frame. 3. Describe the function of a "token" in a token ring network. The token is the mechanism by which nodes are able to determine which system is able to transmit data on the network. A node which holds the token can transmit a certain amount of data, after which it passes the token to the next-in-line node. This node then has the opportunity to transmit before passing the token. In this way, only one node will transmit data at a time. 4. Describe the differences between star, ring, and bus topologies. In a star topology, all connections are point-to-point connections. This is usually implemented through the use of a hub (such as a 10Base-T hub). In a ring topology, each computer is connected to a shared medium (cable), which in turn connects to itself (a self-terminating "ring"). In a bus topology, each node is connected to a shared medium (cable) which is terminated at each end (for example, with a 50-Ohm resister). 5. There are many kinds of physical media over which network traffic can travel. Name three kinds of network physical media. Copper wire: twisted pair, coaxial Fiber optic cabling Wireless: infrared, laser, microwave, radio transmission 6. Define a data communications protocol. a set of rules for interpreting electronic transmissions, defining a common "language" which can permit two network entities to communicate meaningfully 7. Describe the differences between baseband and broadband signalling. Baseband is a kind of digital signalling wherein each medium carries only one channel (signal) of communication. Broadband signalling is typically an analog transmission wherein each medium is capable of carrying multiple channels at a time. 8. Describe the function of a router and why it is important. A router is used to join two networks of the same type. It operates in the network layer and is used to isolate traffic across the entire network, forwarding only the traffic which needs to be forwarded. In this way, a router is able to enhance network performance by reducing network traffic. 9. Explain at least one functional difference between a router and a bridge. A router works in the network layer; a bridge works in the link layer. This means that a bridge is able to join different types of networks, while a router cannot. It also means that a router has the ability to use more complex rules for forwarding traffic--it uses higher level, more complex services. This makes a router more functional, but slower. 10. Name three services provided by the OSI link layer. framing collision detection rudimentary error recovery (retransmission) 11. Name two services provided by the OSI network layer. routing unified addressing scheme node-to-node transmission 12. Name three services provided by the OSI transport layer. process-to-process transmission connection management flow control and buffering resource utilization: multiplexing and parallelization 13. What is the maximum segment length in a 10Base-T network? 100m 14. Name an important funcional difference between the UDP and TCP transport services. UDP is "best effort" delivery--no guarantee TCP attempts to ensure transmission success by trying until recipient's successful response is received 15. Define a multihomed system. a system with multiple network interfaces 16. Name three differences between the SLIP and PPP protocols. PPP permits the use of multiple protocols over the same link PPP uses CRC (cyclic redundancy checks) on every frame for better error detection PPP uses a link control protocol to negotiate many data link options (e.g. dynamic ip address assignment) SLIP is older, more common, slightly faster, and less functional 17. What function does ARP serve? It translates between IP addresses and MAC addresses 18. What function does Proxy ARP serve? It allows host A to impersonate host B and thus answer ARP requests on behalf of host B. The original intention for Proxy ARP was to permit a router to answer an ARP request from a host on one of its networks to a host on another of its networks. 19. Explain the concept of a default route. Default route is a "next-hop" router that the datagram is forwarded to if no other route can be found. 20 Describe the differences between multiplexing and parallelization. Multiplexing means allowing multiple connections to use the same transmission. Parallelization means splitting one connection up to use multiple transmissions. This can result in better (faster) performance for that connection. 21. Describe the differences between passive and active hubs. Passive hubs rebroadcast transmissions to every port automatically. Active hubs are able to rebroadcast transmissions selectively, based on one or more criteria (such as MAC address). 22. 140.129.13.34 is an example of what class IP network address? class B 23. Given the IP address 140.129.13.34 and the netmask of 255.255.255.224, what is the network address for the subnet containing this host? 1000 1100 . 1000 0001 . 0000 1101 . 0010 0010 host address 1111 1111 . 1111 1111 . 1111 1111 . 1110 0000 netmask AND --------------------------------------------- 1000 1100 . 1000 0001 . 0000 1101 . 0010 0000 = 140.129.13.32 24. Given 19.55.7.139/20, how many subnets exist? 0001 0011 . 0011 0111 . 0000 0111 . 1000 1011 host address 1111 1111 . 1111 1111 . 1111 0000 . 0000 0000 netmask (/20) (NETWORK) . ^^^^ ^^^^ . ^^^^ subnet bits 2^(# subnet bits) = # subnets = 2^12 = 4096 25. Given 19.55.7.139/20, how many host addresses exist on each subnet? 1111 1111 . 1111 1111 . 1111 0000 . 0000 0000 netmask (/20) (NETWORK) . ( SUBNET ) ^^^^ . ^^^^ ^^^^ host bits 2^(# host bits) - 2 = # hosts/subnet = 2^12 - 2 = 4094 26. Given the following directory listing: [mshibla@gryphon test]$ ls -l total 7 -rw-rw-r-- 1 mshibla mshibla 47 Jan 25 16:26 exam -rw-rw-r-- 1 mshibla mshibla 29 Jan 25 16:26 file1 -rw-rw-r-- 1 mshibla mshibla 24 Jan 25 16:27 file2 drwxrwxr-x 2 mshibla mshibla 1024 Jan 25 16:25 files -rw-rw-r-- 1 mshibla mshibla 50 Jan 25 16:27 final -rw-rw-r-- 1 mshibla mshibla 18 Jan 25 16:27 grades drwxrwxr-x 2 mshibla mshibla 1024 Jan 25 16:25 trash What is the output after all of the following commands have been executed? [mshibla@gryphon test]$ cat file1 This isn't very interesting. [mshibla@gryphon test]$ cat file2 Unix is cool. I use vi. [mshibla@gryphon test]$ cat file2 >> file1 [mshibla@gryphon test]$ cat file1 [mshibla@gryphon test]$ cat file1 This isn't very interesting. Unix is cool. I use vi. 27. Given the following directory listing: [mshibla@gryphon test]$ ls -l total 7 -rw-rw-r-- 1 mshibla mshibla 47 Jan 25 16:26 exam -rw-rw-r-- 1 mshibla mshibla 53 Jan 25 16:29 file1 -rw-rw-r-- 1 mshibla mshibla 24 Jan 25 16:27 file2 drwxrwxr-x 2 mshibla mshibla 1024 Jan 25 16:25 files -rw-rw-r-- 1 mshibla mshibla 50 Jan 25 16:27 final -rw-rw-r-- 1 mshibla mshibla 18 Jan 25 16:27 grades drwxrwxr-x 2 mshibla mshibla 1024 Jan 25 16:31 trash A. What is the output after all of the following commands have been executed? [mshibla@gryphon test]$ mv final trash [mshibla@gryphon test]$ mv file1 exam [mshibla@gryphon test]$ cp file2 files [mshibla@gryphon test]$ cp grades tests [mshibla@gryphon test]$ rm grades [mshibla@gryphon test]$ rm trash [mshibla@gryphon test]$ rm trash rm: trash: is a directory B. What is the output of the following command? [mshibla@gryphon test]$ ls -l [mshibla@sledge test]$ ls -l total 5 -rw-rw-r-- 1 mshibla mshibla 53 Jan 27 13:08 exam -rw-rw-r-- 1 mshibla mshibla 24 Jan 27 13:05 file2 drwxrwxr-x 2 mshibla mshibla 1024 Jan 27 13:08 files -rw-rw-r-- 1 mshibla mshibla 18 Jan 27 13:09 tests drwxrwxr-x 2 mshibla mshibla 1024 Jan 27 13:08 trash C. What is the output of the following command? [mshibla@gryphon test]$ ls | sort [mshibla@sledge test]$ ls | sort exam file2 files tests trash 28. What is IETF? What is it's function? The Internet Engineering Task Force (IETF) is a large open international community of network designers, operators, vendors, and researchers concerned with the evolution of the Internet architecture and the smooth operation of the Internet. Its mission includes: identifying, and proposing solutions to, pressing operational and technical problems in the Internet; specifying the development or usage of protocols and the near-term architecture to solve such technical problems for the Internet; making recommendations to the Internet Engineering Steering Group (IESG) regarding the standardization of protocols and protocol usage in the Internet; facilitating technology transfer from the Internet Research Task Force (IRTF) to the wider Internet community; and providing a forum for the exchange of information within the Internet community between vendors, users, researchers, agency contractors and network managers. Essay: Answer five of the following (10 pts each): 1. Comprehensively describe the factors which affect the decision of what kind of physical medium to use in a given network segment. 2. Data security is often a concern of network administrators. Describe at least three different kinds of threats to data security and discuss at least two methods designed to address one or more of these problems. 3. The Domain Name System (DNS) plays an integral part in the functionality of the Internet. Describe the functionality of DNS and its component parts. 4. A company has a TCP/IP network which consists of five database servers, eight machines which generate reports on the databases, and six hundred client machines on user's desktops. All of the machines are on 10Base-T networks (with passive hubs), with one subnet containing the servers and the report generators, and three subnets containing the six hundred client machines (two with 254 machines each, and one with the remaining). Management has decided that the network performance (which hasn't been upgraded to keep pace with the company's growth) no longer meets the company's needs. Describe the options available to improve the network's performance, as you would present them to the management. 5. Describe the funcionality of ATM, including its design, its performance, and its common applications and implementations. 6. Traditional computing technologies are increasingly being updated to include network-enabled services. An example of such a network-enabled technology is one of the various implementations of the CORBA specification. Describe the purpose and functionality of CORBA and explain its relationship to earlier object-oriented programming models.