DOC PREVIEW
CMU 15441 Computer Networking - midterm

This preview shows page 1-2-3-4-5 out of 16 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 16 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 16 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 16 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 16 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 16 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 16 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

Carnegie MellonComputer Science Department15-441 Spring 2009MidtermName:Andrew ID:INSTRUCTIONS:There are ?? pages (numbered at the bottom). Make sure you have all of them.Please write your name on this cover and at the top of each page in this booklet except the last.If you find a question ambiguous, be sure to write down any assumptions you make.It is better to partially answer a question than to not attempt it at all.Be clear and concise. Limit your answers to the space provided.A B C D E F G H I Total/ 8 / 10 / 6 / 9 / 6 / 10 / 20 / 8 / 3 / 80A Multiple Choice1. This question tests your understanding of the layers in the Internet Protocol Suite. Foreach item in the list on the right, enter a letter (A–F) from the list on the left to indicatethe corresponding layer.A. applicationB. transportC. InternetD. linkE. physicalF. none of the aboveHTTPTCPUDPIRC routerIPethernetcarrier pigeonManchester encodingSolution:HTTP: (A) ApplicationTCP: (B) TransportUDP: (B) Tr ansportIRC router: (A) ApplicationIP: (C) InternetEthernet: (E) PhysicalCarrier Pigeon: (E) Physical or (F) None of the aboveManchester Encoding: (E) PhysicalB True/FalseUDP uses a 3-way handshakeSONET has a method for resolving clock skewThe cyclic redundancy check for the IP packet header is used primarily to prevent routing loopsOSPF never has ro uting loopsSometimes it is neccessary to gener ate multiple tokens in a token ringCSMA uses exponential backoffThe ethernet spanning tree protocol in guaranteed to maintain shortest paths between nodes in aswitched networkARP can be used to find the IP adresses of computers in an ethernet networkFragmented packets are reasse mbled whenever possible by routersThere are thousands of root nameserversPage 2Solution: False: UDP has no connection s e tup pha se.True: it does have a method.False: CRC is mainly used to check packet integrity.False: Loops can always occur while the network is converging.False: It is never nece ssary to do so.True: CSMA uses exponential backoff for collision reduction and fairness.False: It only maintains s hortest path to the root.False: ARP is used to go from IP to MAC.False: Fragments are only reassmbled at the destination host.False: The number of root name servers is small due to heiarchy.Page 3C Short Answer2. Give an example of a network that is configured to use DHCP, but does not perform any sort of NAT.Solution: CMU’s NetReg and Wireless Andrew systems, for example, use DHCP to provide globallyroutable addresses.Give an example of a network that is configured to use both DHCP and NAT.Solution: A standard consumer “home router” uses such an arrangement by default.What network equipment and configuration would one use to provide Internet access to several comput-ers, including one that acts as a public web server, from a home co nnectio n with a single external IPaddress?Solution: Use a consumer NAT r outer, and either reserve an address via DHCP or manually assignone for the web server. Then, config ure the router to forward the HTTP port through NAT.Page 4D DNS3. For answering the following question, consider the following name servers and the entries their translationtables contain:local name serverName Value Type Classcom ns1.nstld.com NS INns1.nstld.com 192.5.6.32 A INname server ns1.nstld.comName Value Type Classfunsite.com dns.funsite.com NS INdns.funsite.com 128.112.129.1 5 A INname server dns.funsite.comName Value Type Classlotsafun.funsite.com 128.112.136.7 2 A INmanatee.funsite.com 128. 112.155.166 A IN(a) Suppose client1 queries the local name server for lotsafun.funsite.com. The loca l name se rver willrecursively resolve the request and cache the results with a TTL of 10 minutes. Make a diagram ofwhat will happen involving the client and the three nameservers, and writing down all DNS requestsand responses.Page 5(b) DNS generally uses UDP, and each request includes a transaction ID. After issuing a request, aname server listens on the UDP socket for a response that matches the transaction ID. Danny hasnoticed that it takes so me time for the local name s e rver to resolve his requests, and can’t resistthe temptation to cause trouble. He wants to send a single re q uest for lotsafun.funsite.com to hislocal name server, and then trick it into storing (and returning to him) an incorrect translation. IfDanny is willing to spoo f a source address and blast traffic at his loca l name server, how might hepull this off?Solution: The DNS packet the isp asks for can come from Danny. He asks to resolve pa ge,befo re the websites DNS server can r e sponds, he responds as though he is that website’s DNSserver and gives an incorrect result, the actual result from the isp server is thrown out by theisp server. must send a lot of requests and responses to the isp server to get a transaction idmatch.(c) Assume for the next part that each name server can connect to the client or any other nameserverwith RTT = 1.6s and bandwidth 100Mbps. Also, let all DNS packets have size 1 Kbit. For thisproblem assume the loc al server has the result for dns.funsite.com from NS1 cached. There are65536 possible transaction IDs that can be associa ted with a request, and suppose that the localnameserver always choses from among 100 UDP ports to listen for a response. Suppose that boththe transaction ID and the UDP port ar e chosen at random. Given that Danny sends packets asfast as possible to the local name server, what is the probablity he will trick it?Solution: Danny can send at 105kb/s for 1.6 seconds so he c an send 160,000 Kb. So he has160,000 chances to compromise the server in the 1.6 seconds, 1600 00/(100 ∗ 65536) = .02.Page 6E Routing4. Switches and routers are both responsible for forwarding data between networks and network segments,but they operate on different layers and are as a result very different. Please discuss the followingdifferences:(a) How do the addresses differ?Solution: Hierarchical IP addresses versus flat (with resp ect to address look up) 48 bit IEEEaddresses.(b) How does the structure of the forwarding tables differ?Solution: Switches use a simple look up of the flat addresses, e.g. using a content addressablememory. Routers need to deal with CIDR addres s look up, which usually uses tree.(c) What is different about how the forwarding tables are filled in?Solution: Routers use full blown routing protocols such OSPF or BGP. Switches uses a spanningtree protocol.Page 75. For this problem, consider the following network


View Full Document

CMU 15441 Computer Networking - midterm

Documents in this Course
Lecture

Lecture

14 pages

Lecture

Lecture

19 pages

Lecture

Lecture

14 pages

Lecture

Lecture

78 pages

Lecture

Lecture

35 pages

Lecture

Lecture

4 pages

Lecture

Lecture

4 pages

Lecture

Lecture

29 pages

Lecture

Lecture

52 pages

Lecture

Lecture

40 pages

Lecture

Lecture

44 pages

Lecture

Lecture

41 pages

Lecture

Lecture

38 pages

Lecture

Lecture

40 pages

Lecture

Lecture

13 pages

Lecture

Lecture

47 pages

Lecture

Lecture

49 pages

Lecture

Lecture

7 pages

Lecture

Lecture

18 pages

Lecture

Lecture

15 pages

Lecture

Lecture

74 pages

Lecture

Lecture

35 pages

Lecture

Lecture

17 pages

lecture

lecture

13 pages

Lecture

Lecture

21 pages

Lecture

Lecture

14 pages

Lecture

Lecture

53 pages

Lecture

Lecture

52 pages

Lecture

Lecture

40 pages

Lecture

Lecture

11 pages

Lecture

Lecture

20 pages

Lecture

Lecture

39 pages

Lecture

Lecture

10 pages

Lecture

Lecture

40 pages

Lecture

Lecture

25 pages

lecture

lecture

11 pages

lecture

lecture

7 pages

Lecture

Lecture

10 pages

lecture

lecture

46 pages

lecture

lecture

7 pages

Lecture

Lecture

8 pages

lecture

lecture

55 pages

lecture

lecture

45 pages

lecture

lecture

47 pages

lecture

lecture

39 pages

lecture

lecture

33 pages

lecture

lecture

38 pages

lecture

lecture

9 pages

Lecture

Lecture

39 pages

Lecture

Lecture

14 pages

Lecture

Lecture

46 pages

Lecture

Lecture

8 pages

Lecture

Lecture

40 pages

Lecture

Lecture

11 pages

Lecture

Lecture

41 pages

Lecture

Lecture

38 pages

Lecture

Lecture

9 pages

Lab

Lab

3 pages

Lecture

Lecture

53 pages

Lecture

Lecture

51 pages

Lecture

Lecture

38 pages

Lecture

Lecture

42 pages

Lecture

Lecture

49 pages

Lecture

Lecture

63 pages

Lecture

Lecture

7 pages

Lecture

Lecture

51 pages

Lecture

Lecture

35 pages

Lecture

Lecture

29 pages

Lecture

Lecture

65 pages

Lecture

Lecture

47 pages

Lecture

Lecture

41 pages

Lecture

Lecture

41 pages

Lecture

Lecture

32 pages

Lecture

Lecture

35 pages

Lecture

Lecture

15 pages

Lecture

Lecture

52 pages

Lecture

Lecture

16 pages

Lecture

Lecture

4 pages

lecture

lecture

27 pages

lecture04

lecture04

46 pages

Lecture

Lecture

46 pages

Lecture

Lecture

13 pages

lecture

lecture

41 pages

lecture

lecture

38 pages

Lecture

Lecture

40 pages

Lecture

Lecture

25 pages

Lecture

Lecture

38 pages

lecture

lecture

11 pages

Lecture

Lecture

42 pages

Lecture

Lecture

12 pages

Lecture

Lecture

36 pages

Lecture

Lecture

46 pages

Lecture

Lecture

35 pages

Lecture

Lecture

34 pages

Lecture

Lecture

9 pages

lecture

lecture

49 pages

class03

class03

39 pages

Lecture

Lecture

8 pages

Lecture 8

Lecture 8

42 pages

Lecture

Lecture

20 pages

lecture

lecture

29 pages

Lecture

Lecture

9 pages

lecture

lecture

46 pages

Lecture

Lecture

12 pages

Lecture

Lecture

24 pages

Lecture

Lecture

41 pages

Lecture

Lecture

37 pages

lecture

lecture

59 pages

Lecture

Lecture

47 pages

Lecture

Lecture

34 pages

Lecture

Lecture

38 pages

Lecture

Lecture

28 pages

Exam

Exam

17 pages

Lecture

Lecture

21 pages

Lecture

Lecture

15 pages

Lecture

Lecture

9 pages

Project

Project

20 pages

Lecture

Lecture

40 pages

L13b_Exam

L13b_Exam

17 pages

Lecture

Lecture

48 pages

Lecture

Lecture

10 pages

Lecture

Lecture

52 pages

21-p2p

21-p2p

16 pages

lecture

lecture

77 pages

Lecture

Lecture

18 pages

Lecture

Lecture

62 pages

Lecture

Lecture

25 pages

Lecture

Lecture

24 pages

Project

Project

20 pages

Lecture

Lecture

47 pages

Lecture

Lecture

38 pages

Lecture

Lecture

35 pages

Roundup

Roundup

45 pages

Lecture

Lecture

47 pages

Lecture

Lecture

39 pages

Lecture

Lecture

13 pages

Midterm

Midterm

22 pages

Project

Project

26 pages

Lecture

Lecture

11 pages

Project

Project

27 pages

Lecture

Lecture

10 pages

Lecture

Lecture

50 pages

Lab

Lab

9 pages

Lecture

Lecture

30 pages

Lecture

Lecture

6 pages

r05-ruby

r05-ruby

27 pages

Lecture

Lecture

8 pages

Lecture

Lecture

28 pages

Lecture

Lecture

30 pages

Project

Project

13 pages

Lecture

Lecture

11 pages

Lecture

Lecture

12 pages

Lecture

Lecture

48 pages

Lecture

Lecture

55 pages

Lecture

Lecture

36 pages

Lecture

Lecture

17 pages

Load more
Download midterm
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view midterm and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view midterm 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?