CPSC 4240/6240 Spring 2017 HW # 3 v1 Last update: 3/22/2017

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1 CPSC 4240/6240 Spring 2017 HW # 3 v1 Last update: 3/22/2017 You can work individually or with a partner (we won t allow groups > 2). Note that the grading will be identical if you work on your own or with a partner. Just one submission is required per team. Make sure to clearly write both names on all material. Submission instructions: Please submit a PDF that includes all of your answers to turnitin. Question 1- Network Concepts and Analysis The objective of this problem is to deepen your understanding of the following networking concepts (refer to the paragraphs below and material in the attached Appendix A1-A3 for further information): -Network access methods: FDM, TDM, STDM -Traffic models and traffic generators: constant bit rate (CBR), On/Off traffic sources -Traffic shaping and rate control, Network access protocols typically involve one or more of the following methods. We will use the example of a 6 MHz channel that can be accessed using one of the following methods: 1. Frequency division multiplexing (FDM) - allocate to each Host a dedicated subchannel of 2 MHz. 2. Time Division Multiplexing (TDM) - each Host is granted periodic, fixed time intervals to access the 6 MHz channel. Hosts can send data during assigned intervals at the maximum data rate. Hosts are synchronized such that transmissions between different flows never overlap. This requires a scheduler that enforces the TDM structure. 3. Statistical TDM - A Host can access the channel whenever it has data to send. This requires a scheduling component that multiplexes traffic from different Hosts over a shared network resource. In some networks, the access protocol must deal with collisions that can happen when two or more Hosts attempt to transmit at the same time. There are well established approaches to modeling traffic. Implementations of these models can be used as traffic generators. The following are some well known traffic models. The first two are deterministic, the last two are stochastic (i.e., incorporate randomness). 1. Constant packet rate (emulates well known constant bit rate or CBR traffic generator): A Host sends a packet at a fixed rate. 2. Constant burst rate : A Host sends a burst of packets at the maximum data rate and then is idle of a specific amount of time. The cycle repeats forming on/off behavior. 3. Exponential traffic generator : There are different ways to implement this, with the most general method referred to as a Poisson traffic model. In brief, an exponential traffic generator bursts a random amount of data during the On time (the amount is based on an exponential random variable) and with an idle time that is also based on an exponential random variable. 4. Heavy tailed traffic generator - Many specific forms of this, the most notable referred to as a Pareto Traffic Model. A simplified concept is that it is similar to the exponential traffic generator except the distributions are heavy tailed rather than exponential. This means the probability of the random variables being very large is small but the tail of the distribution extends orders of magnitude greater than one based on an exponential distribution. Token bucket rate control. A token bucket filter can be applied at a different levels in a network (link, network, transport, application levels). It can be applied to a single application traffic flow or it can operate on aggregated traffic flows. At can smooth arriving traffic, and shape outbound traffic to a desired average 1

2 rate and with a desired level of On/Off characteristics. Broadband service providers implement services using mechanisms that are likely based on token bucket filters. The perftool client implements a token bucket to control the sending behavior. The config params related to the perftool s token bucket are: avgsendrate : the target sending rate in bits per second tokenbucketsize : maximum size of the bucket in bytes tokensize : the size of each token in bytes msgsize : the amount of application data sent with each message. This question considers the following scenario : Host H1 Host H R Host D1 Host H3 Net 1 Net 2 Token bucket rate control Figure 1.1 Network Scenario (rate control at the application) Net1 is a shared medium network and Net 2 is a point-to-point link. The channel capacity of Net2 is 1 Gbps. Net 1 has a total bandwidth of 6 MHz. The transmission method over Net 1 supports a maximum data rate of 6 Mbps. We consider applications that implement a token bucket rate control mechanism. The output of the rate control from all Hosts (H1, H2, H3) represents the total traffic that is sent over Net 1. Let s assume Net 1 is a shared medium network that handles the case when multiple Hosts send at the same time. Each of the three hosts H1, H2, H3 runs one instance of perfclient (the client side of the perftool). Each client interacts with a single instance of the perfserver. This question considers how the different access network methods might perform subject to different traffic patterns. We identify three experimentalal scenarios that could be applied to the network illustrated in Figure 1.1. Experiment 1: Each Host runs an instance of perfclient interacting with the server at D1. This models a constant packet rate traffic pattern../perfclient D (used by all 3 hosts) Experiment 2: : Each Host runs an instance of perfclient interacting with the server at D1. This models a constant burst rate pattern../perfclient D (used by all 3 hosts) Experiment 3: Each Host runs an instance of perfclient but each is configured slightly differently. This models a constant burst rate pattern but with each Host set with different demands (the avg send rate is different)../perfclient D /perfClient D /perfClient D Question 1a. Explain the tradeoffs between the three network access methods using the above discussion of traffic models and if helpful using the three experiments to help illustrate your answer. HINT: What are the traffic patterns that might cause FDM, TDM, or stdm to not be efficient, fair, or lead to overall good system performance? Specifically, for each Experiment, what is the expected perfclient result (just indicate the avg throughput and possible loss rate the perfclient/server sessions might experience. 2

3 Question 1b. You are to approximate the network illustrated in Figure 1.1 using your VM system (see Figure 1.2). And then you are to run the three experiments. However instead of three separate Hosts (H1, H2, H3), you will simply run three separate instances of perfclient on VM1. You are to use the tc capability of Linux to rate shape aggregate traffic (VM1 to VM2) to a rate of 6 Mbps. Campus network -----Host OS ---- VM1(Ubuntu) ---- VM2(Kali) perfclient perfserver token bucket rate control Figure 1.2 VM Network Setup (with rate control) You are to approximate the network illustrated in Figure 1.1 using your VM system. And then you are to run the three experiments. However instead of three separate Hosts (H1, H2, H3), you will simply run three separate instances of perfclient on VM1 concurrently. You are to use the tc capability of Linux to rate shape aggregate traffic (VM1 to VM2) to a rate of 6 Mbps. Campus network -----Host OS ---- VM1(Ubuntu) ---- VM2(Kali) perfclient perfserver token bucket rate control Figure 1.2 VM Network Setup (with rate control) This will generate 9 perfclient results. Record the avg Throughput and loss rate observed by the server, and the RTT observed by the client. Explain if these experiments reflect a network access method of FDM, TDM, or stdm. Comment on your results in the context of the network access methods and the traffic models presented above. 3

4 Question 2. Assuming your VM setup is similar to Figure 1.2, from VM2, find two different hosts (from different networks) on the Internet that respond to pings. The two choices should reflect to very different paths. Try to find one path that exhibits an average path RTT greater than 60ms (and/or a loss rate of at least 1%). The second path should exhibit a lower average RTT of around 20 ms. We refer to these paths as path #1 and path #2. Once you have found appropriate hosts, perform the following experiments: Run ping for 1 hour to generate 3600 data points for each path. Using matlab (plotdatapdf.m), awk, or excel (or any tool you like) o find the summary statistics (mean RTT and average loss rate). o plot the distribution of the ping RTT data set. On VM2, Issue traceroute to each of the two Internet Hosts. You may need to use ICMP rather than UDP mode. Or you may need to issue the traceroute from your HostOS rather than from your VM2. The objective is to identify the number of routers between VM2 and each of the two Internet Hosts. 4

5 Question 3 following: Issue an ifconfig on an department linux machine. Based on what you see answer the a. What is the subnetwork address in extended network prefix format? b. What is the subnetwork address that this host is directly connected with? c. What is the subnet number? d. Assuming this subnetworking scheme is deployed throughout campus, how many usable subnetworks can be defined? e. How many hosts can exist on the subnetwork that this host is directly connected with? f. Identify the range of host IP addresses (just indicate the first and last address of the block of valid IP host addresses) that can exist on this subnetwork. g. What is the directed broadcast for this subnet? Question 4 Find the aggregate address of a contiguous block of 8 class C network addresses beginning with /24. Do not worry about all 1 or all 0 network prefixes or host ids. So the first IP address in this aggregate block would be Question 5 On your VM (assuming you have SocNetwork-----VM1--- VM2, do this from VM2), ping a nonexistent host by issuing ping -c Using tcpdump, capture all packets that are sent and received as a result of this invocation of ping. You should see one arp frame. Note: you might see some extraneous arp frames just ignore. You might also capture other packets that we are not interested in. To capture just icmp and arp, and to make sure to capture ALL the data in the packets, issue tcpdump as follows: sudo tcpdump -s w trace.dmp 'arp or icmp' To create a readable version of the trace: sudo tcpdump X s 1500 r trace.dmp > trace.trace a. Before issuing the ping, issue an arp to see the contents of the arp cache. After you issue the ping, recheck the arp cache. Explain what you see in the context of this problem. Keep this simple.one very brief sentence should be sufficient. b. Print (and include in your submission) the tcpdump ascii formatted trace of the arp frame. c Identify the sender s MAC address in the trace. Print on your submission the MAC address in hex format. Make sure you state your answer in proper network byte order. d. Repeat, but now add a bogus arp table entry in your VM (destination IP address of and use a bogus MAC). Use tcpdump and capture the network flows when you issue the same ping. Show the tcpdump readable result (any ICMP and ARP frames) and provide a one sentence explanation for what you find. 5

6 Question 6 DNS On your VM, issue a host v and use tcpdump to trace the data. Make sure the tcpdump trace includes the data contained in the packets. Note: Feel free to use dig instead of host. Also, feel free to use any other valid domain name. sudo tcpdump X s 1500 r dns.dmp > dns.trace Include the ascii formatted tcpdump text trace. Identify the name (IP address and domain name) of the DNS server that your DNS client directly interacts with. Please identify the octets that give the IP address associated with the answer. Please identify the TTL value that is associated with this answer (circle the octets and give the timeout as an integer number of seconds). Please indicate if the answer was authoritative or not (identify the data in the trace that shows this). Question 7 for 6240 students only (4240 students can do this and earn up to 5 extra credit points for this homework) Add IP V6 support to the currnet UDPEchoV1-2.tar.gz tool. Add a optional parameter to the client to specify IP v4 or IP v6. For the server, add the same parameter but include a third option which is either. For the client, IP v4 should be the default. For the server, the either IP v4 or IP v6 option should be the default. At the server side, please use a select to deal with handling two different sockets (one for IP V4, one for IP V6). Do basic testing and in one page document several test cases and copy/paste the results. Submit this with your HW3 pdf submission to turnitin. Submit your updated UDPEchoV1-2 using handin. 6

7 Appendix 1. Additional Material Figure A1. Excerpt from Tanenbaum s Computer Networks : TDM, STDM Figure A2. Excerpt from Tanenbaum s Computer Networks : Nyquist and Shannon s thm 7

8 Figure A3. Token Bucket Algorithm 8