Lab Introduction

Test Machines

We have a set of three identical test networks available for your use during the lab sessions. Each test network consist of three machines - two hosts and one dummynet router. All three machines are Intel PCs running FreeBSD.

All of the machines have connections to the SDSC networks. We call these interfaces the public interfaces, and the public IP addresses for these interfaces range from to as shown in the attached network maps.

In each group of 3 machines, the hosts both have a private 100 Mb/s connection to the dummynet router. Routing is set up so that there are a total of 6 virtual networks connecting the two hosts. These virtual networks are given IP addresses out of the private address space. The hosts have been given names as shown in the following table to make referring to them easier:

Box 1 name Box 1 IP address Box 3 name Box 3 IP address
a-10 b-20
a-11 b-21
a-12 b-22
a-13 b-23
a-14 b-24
a-15 b-25

The router IP address is always ".1", and the host IP address is always ".2". Machines in groups 4-6 and 7-9 use the same set of private IP addresses to form their virtual networks.

The router is configured with dummynet, a tool available in FreeBSD to create virtual networks. Dummynet has been used to create a number of interesting network topologies within the router. A different topology is configured for each of the first four virtual networks; the final two virtual networks are available for use by the groups in creating their own topologies.

Because we have only three test networks, students will need to share them. Labs will be done in groups of 3-4 people; each test network will have 2 groups sharing it. Because there are 6 virtual networks available within each test network, it should be possible to share without conflicting too much. Students have accounts on each of the lab machines.

You can use ssh to log into the machines from your NT workstation in the cluster. In order to use X-windows applications, you will need to run the X server on the local Windows NT workstation. You may need to authorize the lab machines to access your workstation X server, and you may also need to set your DISPLAY environment variable on the lab machines.

Tools Information

Most of the tools are installed in /usr/local/bin on the test machines. In this directory you will find both tcptrace and xplot. In addition, you will find ttcp, a tool for running TCP tests.

You will need to run tcpdump in order to collect packet traces. Tcpdump normally requires root access, but we have enabled all of the students to access it using the sudo command. In order to use tcpdump, you need to preface the command with sudo as follows:

sudo tcpdump -i xl0 -w mytcpdump.out
(Note that the network interface is "xl0", not "x10").

Sources for the tools we are using are available at