Networking 1

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timer Asked: Nov 27th, 2016

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1. IP Fragmentation (5 pt.) (show all the details/work) Consider sending a 2400-byte datagram into a link that has an MTU of 700 bytes. Suppose the original datagram is stamped with the identification number 422. a. How many fragments are generated? b. What would be the identification number for each fragment? 2. HOL Blocking (4 pt.) (show all the details/work) What is HOL blocking? Does it occur in input ports or output ports? 3. Error Detection Code (10 pt., 5 pt. each) (show all the details/work) Suppose the information portion of a packet (D in Figure 5.3) contains 10 bytes as follows: D: 01001100 01101001 01101110 01101011 00100000 01001100 01100001 01111001 01100101 01110010 a. Suppose an even parity scheme is being used. Comment on how this parity is computed and then compute a parity bit for each row. b. Now consider an odd parity scheme, comment on how this parity is computed and compute the 2D parity bits for D. What would the value of the field containing the parity bits be for the case of a two-dimensional parity scheme? Assume the bits in D are divided into 10 rows and 8 columns (i.e., each byte is a row). 4. CRC (8 pt.) (show all the details/work) Consider the 7-bit generator, G=10011, and suppose that D has the value 1010101010 (10 bits). What is the value of R? 5. LAN Addressing (24 pt.) (show all the details/work) Consider the following three (3) LANs interconnected by two routers, with assigned IP/MAC addresses for hosts and routers in the network. C E 00-00-00-00-00-00 192.168.2.001 44-44-44-44-44-44 192.168.3.001 77-77-77-77-77-77 LAN Router 1 LAN Router 2 LAN 88-88-88-88-88-88 11-11-11-11-11-11 192.168.3.003 F 99-99-99-99-99-99 Suppose Host A sends a datagram to Host F. a. Provide MAC addresses and IP addresses for the interfaces at Host A, both routers, and Host F. Give the source and destination MAC addresses in the frame encapsulating this IP datagram as the frame is transmitted (Also give the source and destination IP addresses in the IP datagram encapsulated within the frame at each of these points in time.) (show all the details/work): (i) from A to the left router: Source MAC address: Destination MAC address: Source IP: Destination IP: (ii) from the left router to the right router: Source MAC address: Destination MAC address: Source IP: Destination IP: (iii) from the right router to F: Source MAC address: Destination MAC address: Source IP: Destination IP: b. Suppose now that the leftmost router in Figure above is replaced by a switch. Hosts A, B, C, and D and the right router are all star-connected into this switch. Give the source and destination MAC addresses in the frame encapsulating this IP datagram as the frame is transmitted (Also give the source and destination IP addresses in the IP datagram encapsulated within the frame at each of these points in time.) (show all the details/work): i) from A to switch: Source MAC address: Destination MAC address: Source IP: Destination IP: ii) from switch to right router: Source MAC address: Destination MAC address: Source IP: Destination IP: iii) from right router to F: Source MAC address: Destination MAC address: Source IP: Destination IP: 6. Switch Table (8 pt.) (show all the details/work along with the table) Let’s consider the operation of a learning switch in the context of a network in which 6 nodes labeled A through F are star connected into an Ethernet switch. Suppose that (i) B sends a frame to E, (ii) E replies with a frame to B, (iii) A sends a frame to B, (iv) B replies with a frame to A. The switch table is initially empty. Show the state of the switch table before and after each of these events. For each of these events, identify the link(s) on which the transmitted frame will be forwarded, and briefly justify your answers using the table below. Action Switch Table State Link(s) packet is forwarded to Explanation 7. Link State Routing (21 pt.) (show all the details/work along with the table) Consider the following network. With the indicated link costs, use Dijkstra’s shortest-path algorithm to compute the shortest path from “x” to all network nodes. Show how the algorithm works by computing the table below. Note: If there exists any tie in each step, choose the left-most column first. Step N’ D(t),p(t) D(u),p(u) D(v),p(v) D(w),p(w) D(y),p(y) D(z),p(z) 0 1 2 3 4 5 6 8. Network Address Translation (10 pt.) (show all the details/assumptions/work along with the table) Consider the following network setup. Suppose that the ISP instead assigns the router the address 24.34.112.235 and that the network address of the home network is 192.168.1/24. Assume IP addresses in the home network as follows: 192.168.1.1, 192.168.1.2, 192.168.1.3 with the router interface being 192.168.1.4 Suppose each host has two ongoing TCP connections (i.e., 6 connections for three hosts in the figure), all to port 80 at host 128.119.40.86. Provide the six corresponding entries in the NAT translation table. Assume that the router assigns the WAN side port number from 4000 and increments, and that each host assigns a source port number incrementally from 3345 to 65535. Refer to Figure 4.22 in the textbook and slide 4-61. NAT translation table WAN side address LAN side address 9. Hand-on Practice: WireShark (10 pt., 5 pt. each) a. Capture packets and choose one. Show the Ethernet information and attach the screenshot with the submission document as your answer to this part. What are the source address, destination address, and type? Explicitly report the information. b. Capture a screen shot for a DHCP packet. Give a brief explanation of the DHCP packet you captured.

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