Exercises: Local Network Analysis Tools

Unix/IP Preparation Course
Summer Network Design Workshop - July 2009
Eugene, Oregon


See what services are running on your machine. You can use the
presentation as a reference:


Or, utilize "man lsof", "man netstat", "lsof -h" y "netstat -h" to see
the available options (there are a lot!). Remember to use
sudo when using lsof and netstat.

* Using lsof, what IPv4 services are listening on your machine?

* Using netstat, what IPv4 and IPv6 services are listening on your machine?


To use tcpdump you need to use sudo. To use wireshark you need to open
a terminal and use sudo as a normal user (i.e., userid

* 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 install wireshark:

  $ sudo apt-get install wireshark

* Once installed, in another terminal as a normal user ("sysadmin") open
  wireshark like this:

  $ sudo wireshark -r /tmp/tcpdump.log

  Now you can play with the wireshark interface to start and
  understand how it works. Can you figure out how to follow packets
  by protocol? Session?

  Now try something like this (note the "eth1"):

  $ sudo rm /tmp/tcpdump.log
  $ sudo tcpdump -i eth1 -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: anything you want
  ftp> exit

  And, end the tcpdump session in the other terminal (CTRL-C). Now
  view the contents of the log file:

  $ sudo wireshark -r /tmp/tcpdump.log

  Can you see your password? Sniffing passwords on wireless lans is
  very easy with a tool like this.

Use "man iperf" or "iperf -h" for help.

* First install iperf:

  $ sudo apt-get install iperf

* 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 laptops to a switch, configuring
  your eth0 interface with an IP address and doing the previous
  step again with this faster connection. How does it look?

* 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.