Homework Assignment 2 Due Oct 11 3 50 PM EE122 Introduction to Communication Networks Fall 2006 Department of Electrical Engineering and Computer Sciences College of Engineering University of California Berkeley Vern Paxson Sukun Kim Dilip Antony Joseph 1 Peterson Davie Exercises 3 1 3 6 4 4 2 The Design of IP IP includes two options for including a source route that is the sender of the datagram specifies a sequence of intermediary routers that the packet should traverse on its way to the destination Both of these options have 3 bytes of meta information essentially an option header followed by a series of 4 byte IP addresses specifying the intermediary routers Given the constraints imposed by the design of the IP header what is the largest number of routers that such an option can include 3 Subnetting and Classless Interdomain Routing CIDR Your company BearsEx is assigned 4 blocks of 256 addresses from your ISP 147 17 204 0 255 147 17 205 0 255 147 17 206 0 255 and 147 17 207 0 255 a If your ISP used class A B C subnetting what would be the subnet mask and the subnet number b In this case what corresponding network prefix es appear to routers outside of the ISP c If instead your ISP uses classless interdomain routing CIDR and assigns 197 17 204 0 255 197 17 205 0 255 197 17 206 0 255 and 197 17 207 0 255 to BearsEx what are the corresponding network prefix es that appear to routers outside of the ISP 1 4 Comparison of Stop and Wait and Sliding Window You want to transfer a file from Berkeley to San Francisco For this problem assume the following The size of file is 90 000 bytes It will be transferred in 1 500 byte data packets for which 40 bytes are taken up with headers The size of acknowledgement packets is 40 bytes including header Every packet is acknowledged The communication is bidirectional and the bandwidth is 100 Mbps megabits sec in each direction Hosts can send and receive at the same time The latency from Berkeley to San Francisco is 5 ms as is the latency in the opposite direction Assume that time to process a packet is very small so the receiver can send an acknowledgement as soon as it receives a data packet but not before it receives the entire data packet Likewise for sliding window the sender can send packets back to back to the degree that the window size permits Assume no packet loss a With Stop and Wait how long will it take to transfer the file b What is the corresponding throughput total amount of user data transferred so 90 000 bytes over the total time required to transfer it c With Sliding Window with SWS RWS 3 how long will it take to transfer the file What is the throughput d If SWS and RWS are set to the bandwidth delay product bandwidth of the path times the roundtrip latency of the path then how long does it take to transfer the file and with what throughput e Extra credit if SWS and RWS are set to twice the bandwidth delay product how long does the transfer take with what throughput and why 5 DNS Repeatedly use the command dig norecurse dns server c199 eecs berkeley edu to locate the IP address of c199 eecs berkeley edu starting with a root servers net as the first dns server a Which DNS servers do you visit in the process of finding the address b What is the address c What happens if instead you look up c199 berkeley edu i e you forget to include eecs 2 6 Email In this problem you will send an email which looks like http inst eecs berkeley edu ee122 fa06 hw email content txt The file http inst eecs berkeley edu ee122 fa06 hw tracefile contains a tcpdump trace showing an SMTP client connecting to an SMTP server to send an email a Taking the actions of the client as a template use the telnet tool to send an email to binetude calmail berkeley edu not binetude eecs berkeley edu with the subject My Answer To Homework 2 Problem 4 and where your username is annotated in some obvious fashion like Golden Bear in the example When you do this record your connection with tcpdump tcpdump s 0 w tracefile host calmail eecs berkeley edu and port 25 and submit the trace as documentation along with a transcript of the commands you used to send the email including commands like HELO IMPORTANT You need to inspect tracefile to see whether it contains any activity other than your own which can happen if someone else also sent email at the same time If so you need to filter the trace using your SMTP client s ephemeral port number It will be useful to use your calmail account when you testing so you can see the resulting email b An open relay is an SMTP email server configured in such a way that it allows anyone on the Internet to relay email through it to a recipient who is not directly served by the server Repeat the exercise but when connecting specify a recipient of vern icir org to the server What response do you receive Submission Instructions 1 Make sure you are registered with the EECS instructional account system different from registration for the class You would have been prompted to register the first time you logged in to your instructional account You can check your registration status by running the command check register If you find yourself not registered run the command register 2 Log in to your instructional account 3 Create a directory called hw2 mkdir hw2 4 Change to that directory cd hw2 5 Copy all the files that you wish to submit to this directory 6 Run the submit program submit hw2 7 Make sure that no error messages are displayed If some error occurs retry If it still occurs contact the TAs 3
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