Final Exam for ECE671 Spring /29/18

Transcription

1 ECE67: Eam II Final Eam for ECE67 Spring 28 3/29/8 Instructions: Put our name and student number on each sheet of paper! The eam is closed book. You have 75 minutes to complete the eam. Be a smart eam taker - if ou get stuck on one problem go on to another problem. Also, don't waste our time giving irrelevant (or not requested) details. The total number of points for each question is given in parenthesis. There are points total. Show all our work. Partial credit is possible for an answer, but onl if ou show the intermediate steps in obtaining the answer. If ou make a mistake, it will also help the grader show ou where ou made a mistake. Good luck. Problem Ma. Points Points Total

2 ECE67: Second Eam 2 Problem : (Quickies 32 Points (4 each)) a. Wh is Google able to use QUIC in a large-scale in the Internet? A: For each and ever session between a chrome browser and an of its web servers it can use whatever protocol on top of UDP or TCP it wishes to implement. UDP is the obvious choice for QUIC since it gives the application protocol (QUIC in this case) more freedom. b. What rule needs to be implemented in a firewall if it should allow access to our institution web server, which has as IP address outside our institutional network? Give answers in the form of Source IP, Dest IP, Source Port, Dest Port!) A:*, , *, 8; c. Does the shortest path routing protocol represent a centralied or distributed approach? What about a routing protocol that is based on the distance vector algorithm? For each tpe of routing protocol name a version that is defined as an Internet standard A: centralied (OSPF, RFC 2328), distributed (RIP, RFC 2453). d. In the case of Internet routing eplain the difference between data and control plane! A: Data plane: regular traffic, control plane: routing information, monitoring data, error handling. e. QUIC makes use of an UUID. What s the benefit of emploing this UUID? A: In TCP a 5-tupel (Src IP, dest. IP, source port, dest port, proto) is required to identif a session. These parameters partl change if a mobile client, e.g., changes WiFi to LTE and the session cannot be easil identified. This is different if a UUID is used. The flow can still be identified even if the client s IP address has changes. f. Eplain wh there has been a recent effort to split a TCP session in one or more subflows that are routed over different paths (Multi-path TCP)? Wh was this not considered in TCP s original design? A: Mobile devices and servers in data centers have more than one network interface (multi-homing) and data can be routed via different paths. In addition, ISPs tend to route data over multiple paths. This was not the case in the beginning of the Internet where the onl devices with more than one interface were routers. g. What fields in the IP header of a packet that is transmitted the LAN to the WAN have to be changed in the case of NAT? What fields in the TCP header of a packet that is transmitted the LAN to the WAN have to be changed in the case of NAT? A: Source Address and Checksum. Source Port and Checksum. h. What two tpes of sequence numbers are used in MPTCP. What are these sequence numbers used for? A: Regular TCP sequence numbers and DSeq. The former is used as in traditional TCP sessions. DSeq is used to identif the position of a MPTCP segment s paload in the application-level bte stream.

3 ECE67: Eam II 3 Problem 2: NAT (24 Points) For this problem, make ourself familiar with Figure. 2 S: D: S: S: D: D: S: D: A B C D Figure a. (5 Points) Assign IP addresses and subnet mask to hosts A-D. A: netmask, e.g.: b. (6 Points) Fill out the blank fields in Figure b entering the appropriate IP addresses. (Note, that -4 show a sequence of a packet going the local network to a server with IP address and back.) c. (8 Points) For the communication sequence for problem b) complete Table. In addition, add an entr for a communication with an node in the network that connects to the interface of the NAT router that has IP address In both cases, port numbers can be randoml selected! Table NAT Translation Table WAN LAN A: NAT Translation Table WAN side addr, port LAN side addr, port , 5..., , 5...3, 3345

4 ECE67: Second Eam 4 f. (2 Points) Eplain wh the NAT Translation Table also needs to store the WAN side IP address in addition to the port? A: The NAT can be connect to more than one Internet provider and duplicate port number entries can be assigned for connections to different access networks. To find the matching entr on the LAN side the IP address, port number pair is required on the WAN side g. (3 Points) Describe briefl how ou would implement NAT functionalit in an SDN controller! A: An SDN controller would implement the data structure of the NAT Translation Table. In addition, it would implement the forwarding rules to send out a packet the correct interface and the rules necessar to make the required header modifications. Problem 3: Dijkstra (2 Points) a. (4 Points) Consider the following network (Figure 2). With the indicated link costs, use Djikstra s shortest-path algorithm to compute the shortest path A to all network nodes. Show how the algorithm works b computing the table below. 4 E F 7 G 5 H A B C D 5 6 Figure 2 step N D(B),p(B) D(C),p(C) D(D),p(D) D(E),p(E) D(F),p(F) D(G),p(G) D(H),p(H) A

5 ECE67: Eam II A: step N D(B),p(B) D(C),p(C) D(D),p(D) D(E),p(E) D(F),p(F) D(G),p(G) D(H),p(H) A A,E A,E,B A,E,B,C A,E,B,C,D A,E,B,C,D,F A,E,B,C,D,F,G A,E,B,C,D,F,GH b. (6 Points) For the network shown below show the information in the routing tables of nodes,, and in the second iteration of the algorithm. The initial state of the tables of all three nodes is also shown below. 2 7 node table cost to 2 7 node table cost to 2 node table cost to 7 A: cost to

6 ECE67: Second Eam 6 Problem 4: LPM and TCAM (24 Points) a. (6 points) Given the following forwarding table, create a binar tree that allows longest prefi match lookup. Interface A /4 B /2 C /3 D /4 E /2 F / Prefi Answer: F E B C A D b. (4 Points) In that binar graph ou created show how a search for the appropriate interface for address would be performed. Please indicate the individual steps in the correct order. Answer: c. ( Points) Show how a TCAM realiation for the following forwarding table would look like. Enter ou solution in Figure 3. Interface A B * C ** Prefi

7 ECE67: Eam II 7 D ** Figure 3 Answer:

8 ECE67: Second Eam 8 X X X X X d. (4Points) Consider a datagram network using 8-bit host addresses. Suppose a router uses longest prefi matching and has the following forwarding table: Prefi Match 2 otherwise 3 Interface For each of the four interfaces, give the associated range of destination host addresses and the number of addresses in the range. Answer: Destination Address Range Link Interface through (32 addresses) through (64 addresses) through (32 2 addresses) through (28 3 addresses)