To start a tftp server use the lab server below the table. The files will be stored in the /var/lib/tftpboot directory. Starting and stopping is done via

sudo service tftpd-hpa status
sudo service tftpd-hpa start
sudo service tftpd-hpa stop

The tftp server will listen on port 69 for connections. You can test the setup on the localhost by opening a new shell and doing

echo "Hallo hier bin ich!!!" > hallo.txt
tftp localhost
trace
> put hallo.txt
> quit

This will create a new file “hallo.txt”. This file is then transferred to server and is visible in the /var/lib/tftpboot directory.

In order to create a zero filled file “neu.txt” with 50MByte size you can use

dd if=/dev/zero of=neu.txt bs=1M count=50

Now start the server on the lab pc and the client on your laptop. Test the tftp connection by transferring “hallo.txt” from the client to the server. Run wireshark on the client and on the server to observe the packets which are transferred. Sketch a message sequence chart.

Now do the big thing:

1. Create a file with a size of 50 MByte
2. Use ping to estimate the round trip time between the two computers
3. Estimate the expected transfer time for the file
4. Transfer the file and compare the measurement data with your calculation.

Modify the ethernet speed to 10 MBit/s and measure again. Set the ethernet speed back to 100MBit/s after the measurement.

Configure the lab pc on the top shelf with the two network cards as bridge.

sudo brctl addbr my bridge
sudo brctl addif mybridge eth2
sudo brctl show
sudo brctl addif mybridge eth3
sudo ifconfig eth2 0.0.0.0
sudo ifconfig eth3 0.0.0.0
sudo ifconfig mybridge up

The bridge should now be up and running. Cable the pc as bridge between lab pc and laptop and test the connection.

In order to add 50 ms delay to the outgoing traffic on the bridge.

sudo tc qdisc add dev eth2 root netem delay 50 ms

To modify the delay setting use

sudo tc qdisc change dev eth2 root netem delay 10 ms

To add a packet loss, you can do

sudo tc qdisc change dev eth2 root netem delay 10 ms loss 10.0%

• Create a file with 1 MByte size
• Configure the bridge with no delay
• Measure the tftp transfer time over the bridge
• Do a ping RTT analysis. What is RTT according to ping?
• Add a delay of 20 ms to each ethernet device on the bridge computer
• Measure ping RTT again.
• Measure the tftp transfer time again.
• Set the delay to 30 ms and to 40 ms and measure again.

Analyze and compile the tcp client and server programs “client.c” and “server.c”.

• Run the server on one PC and the client on the laptop
• Run wireshark to analyze the tcp connection. Sketch a message sequence diagram
• Modify the server and client code to transfer about 1 MByte of data as fast as possible
• Measure the transfer time over the tcp connection over the bridge with no delay.
• Measure the speed with iperf
• Add a delay of 10ms to each ethernet device in the bridge and do the measurement again.
• Measure with 20ms, 30ms and 40ms