Network Performance Definitions and Measurement Exercises ========================================================= Notes: ------ * Commands preceded with "$" imply that you should execute the command as a general user - not as root. * Commands preceded with "#" imply that you should be working as root. * Commands with more specific command lines (e.g. "GW-RTR>" or "mysql>") imply that you are executing commands on remote equipment, or within another program. * If a command line ends with "\" this indicates that the command continues on the next line and you should treat this as a single line. Exercises Part I ================ 0. Log in to your PC/VM or open a terminal window as the sysadm user. Network Performance Metrics --------------------------- 1. ping ------- ping is a program that sends ICMP echo request packets to target hosts and waits for an ICMP response from the host. Depending on the operating system on which you are using ping you may see the minimum, maximum, and the mean round-trip times, and sometimes the standard deviation of the mean for the ICMP responses from the target host. For more details see: http://en.wikipedia.org/wiki/Ping Blocking ping is generally a bad idea. With all this in mind, try using ping in a few different ways: $ ping localhost Press ctrl-c to stop the process. Here is typical output from the above command: PING localhost (127.0.0.1) 56(84) bytes of data. 64 bytes from localhost (127.0.0.1): icmp_seq=1 ttl=64 time=0.020 ms 64 bytes from localhost (127.0.0.1): icmp_seq=2 ttl=64 time=0.006 ms 64 bytes from localhost (127.0.0.1): icmp_seq=3 ttl=64 time=0.006 ms 64 bytes from localhost (127.0.0.1): icmp_seq=4 ttl=64 time=0.006 ms 64 bytes from localhost (127.0.0.1): icmp_seq=5 ttl=64 time=0.006 ms 64 bytes from localhost (127.0.0.1): icmp_seq=6 ttl=64 time=0.009 ms 64 bytes from localhost (127.0.0.1): icmp_seq=7 ttl=64 time=0.007 ms ^C --- localhost ping statistics --- 7 packets transmitted, 7 received, 0% packet loss, time 5994ms rtt min/avg/max/mdev = 0.006/0.008/0.020/0.005 ms Question: why did the first ICMP response take 20ms while the remaining responses were much quicker? This is a type of delay. What kind is it? 2. traceroute ------------- You may have used traceroute before, but have you really looked at what it is doing? If not, read this: http://en.wikipedia.org/wiki/Traceroute Now try: $ traceroute nsrc.org Here's sample output from traceroute to nsrc.org (lines wrapped due to length): traceroute to nsrc.org (128.223.157.19), 30 hops max, 60 byte packets 1 192.168.5.129 (192.168.5.129) 4.291 ms 5.757 ms 6.725 ms 2 192.168.17.2 (192.168.17.2) 1.933 ms 1.932 ms 2.150 ms 3 192.168.0.1 (192.168.0.1) 2.140 ms 2.127 ms 2.598 ms 4 10.0.0.129 (10.0.0.129) 2.586 ms 2.576 ms 4.548 ms 5 (168.234.72.1) 4.792 ms 4.786 ms 4.750 ms 6 200.0.204.69 (200.0.204.69) 7.456 ms 5.665 ms 5.890 ms 7 panama-salvador.core.redclara.net (200.0.204.185) 64.651 ms 64.884 ms 64.870 ms 8 panama-santiago.core.redclara.net (200.0.204.22) 124.865 ms 124.853 ms 124.841 ms 9 saopaulo-santiago.core.redclara.net (200.0.204.38) 172.008 ms 171.793 ms 172.019 ms 10 ge-7-1-0.0.rtr.chic.net.internet2.edu (64.57.28.114) 172.006 ms xe-2-2-0.88.rtr.wash.net.internet2.edu (198.32.11.105) 244.441 ms 244.675 ms 11 xe-0-1-0.0.rtr.atla.net.internet2.edu (64.57.28.6) 258.151 ms 258.384 ms 258.618 ms 12 xe-0-0-0.0.rtr.salt.net.internet2.edu (64.57.28.24) 207.383 ms 207.602 ms xe-1-0-0.0.rtr.hous.net.internet2.edu (64.57.28.112) 282.040 ms 13 xe-2-0-0.0.rtr.losa.net.internet2.edu (64.57.28.96) 314.004 ms xe-1-0-0.0.rtr.seat.net.internet2.edu (64.57.28.105) 224.293 ms 224.527 ms 14 vl-101.xe-0-0-0.core0-gw.pdx.oregon-gigapop.net (198.32.165.65) 328.948 ms vl-102.xe-1-0-0.core0-gw.pdx.oregon-gigapop.net (198.32.163.69) 227.015 ms vl-101.xe-0-0-0.core0-gw.pdx.oregon-gigapop.net (198.32.165.65) 328.184 ms 15 vl-105.uonet9-gw.eug.oregon-gigapop.net (198.32.165.92) 330.660 ms 330.891 ms 229.940 ms 16 vl-3.uonet2-gw.uoregon.edu (128.223.3.2) 331.359 ms 229.748 ms 229.727 ms 17 nsrc.org (128.223.157.19) 229.458 ms 229.460 ms 330.862 ms Do you understand what each item means? If not, see the Wikipedia page and type: $ man traceroute for more information. What does it mean if you see lines like this? 15 * * * 16 * * * 17 * * * Again, read "man traceroute" for details. As you can see traceroute can be used to determine where problems are taking place between two endpoints on a network. 3. mtr ------ The mtr tool combines ping and traceroute in to a single, dynamically updating display. Give it a try: $ mtr nsrc.org The output of the command looks different on different Linux and UNIX flavors, but in general you'll see a summary of packet loss to each node on the path to the remote target host, number of ICMP echo request packets sent, last rtt (round-trip-time) to the host, average, best and worst rtt as well as the standard deviation of rtt's. By showing the percent loss of packets in this format it makes it much easier to see where you may be having network issues. 4. ping with variable packet size --------------------------------- By default, ping sends out IP datagrams of size 84 bytes: * 20 bytes IP header * 8 bytes ICMP header * 56 bytes data padding However, you can send out larger packets using the -s option. Using `-s 1472` will give you a 1500-byte IP datagram, which is the maximum for most networks before fragmentation takes place (MTU = Maximum Transmission Unit) This simple mechanism can be used to debug all sorts of problems, and even distinguish between transmission delay and propagation delay. For this exercise, first determine your default gateway, which is the first hop in a traceroute, or use `netstat -rn` for destination 0.0.0.0 Send 20 standard pings to that address: ping -c20 10.108.240.254 Make a note of the *minimum* round-trip time seen (t1). Now send 20 maximum-sized pings: ping -c20 -s1472 10.108.240.254 Again, make a note of the *minimum* round-trip time seen (t2). The propagation delay is the same in both cases, so the larger round-trip time must be due to transmission delay. You can now estimate the transmission delay and hence the bandwidth of the link. increase in transmission time = t2 - t1 increase in bits sent = (1500-84) * 8 * 2 = 22656 (x2 because the round-trip time involves sending the packet twice) Divide the bits by time to get an estimate of bits per second. Remember to convert milliseconds to seconds first. By doing this for subsequent hops, it's possible to estimate the bandwidth on each hop, even those remote from you. There is a tool available which does this automatically - it's called "pathchar" but you have to build it from source. --------------------------------------------------------------------------- Exercises Part II ================= Network Analysis ---------------- 1. lsof and netstat ------------------- See what services are running on your machine. You can use the presentation as a reference. Or, utilize "man lsof", "man netstat", "lsof -h" and "netstat -h" to see the available options (there are a lot!). Remember to use sudo when using lsof and netstat to give yourself necessary permissions to view everything. * Using lsof, what IPv4 services are listening on your machine? * Using netstat, what IPv4 and IPv6 services are listening on your machine? 2. tcpdump and tshark --------------------- To use tcpdump you need to use sudo, or be root. To use wireshark you need to open a terminal and use sudo as a normal user (i.e. userid "sysadm"): Use tcpdump like this: $ sudo tcpdump -i lo -A -s1500 -w /tmp/tcpdump.log Now, generate some traffic on your lo interface in another terminal. For example: $ ping localhost $ ssh localhost etc. Afterwords press CTRL-C to terminate the tcpdump session. Note: ssh generates much more "interesting" output. Now let's read the output from tcpdump using shark: $ sudo tshark -r /tmp/tcpdump.log | less What do you see? Can you follow the SSH session you initiated earlier? Now try something like this: $ sudo rm /tmp/tcpdump.log $ sudo tcpdump -i eth0 -A -s1500 -w /tmp/tcpdump.log In another terminal do: $ ftp limestone.uoregon.edu Connected to limestone.uoregon.edu. 220 FTP Server ready. Name (limestone.uoregon.edu:sysadmin): anonymous Password: ftp> exit End the tcpdump session in the other terminal (CTRL-C). Now view the contents of the log file: $ sudo tshark -r /tmp/tcpdump.log | less Can you see your password? If you have a lot of traffic on your network, then the tcpdump.log file may be fairly large. You can search for your FTP session by typing: "/FTP" in the output screen. Since you piped your shark command output to the "less" command using the "/" to search for strings works. Now press the "n" key for "n"ext to follow the FTP session. You should see a line with the string: "FTP Request: PASS PasswordYouTypedIn" Sniffing unencrypted passwords on wireless lans is very easy with a tool like this. 3. Using iperf -------------- Use "man iperf" or "iperf -h" for help. Ask your neighbor to run: $ iperf -s Connect to your neighbor's machine using: $ iperf -c ipNeighbor How is the throughput between your machines? Consider connecting both your PCs directly together (one cable, no switch). Use a private IP address on both machines, verify you can ping each other, then repeat the previous steps with your new connection. Has your throughput improved? If you have time continue playing with iperf options. If you have a remote PC running UNIX or Linux you might want to try installing iperf and testing your connection from the workshop lab to your remote machine. Some more things to try... * Test TCP using various window sizes (-2). * Verify TCP MSS (-m). How does this affect throughput? What is Path MTU discovery? * Test with two parallel threads (-P) and compare the totals. Is there any difference? Why? * Test with different packet sizes and the TCP_NODELAY (-N) option.