The Actual Labs
LAB 1 (20 points)
Mininet allows us to set link parameters from the command line. If we specify a link of type tc, the software can limit the bandwidth and the delay for each link. We can also run bandwidth tests for us via the iperf command.
The default mininet topology is two ‘hosts’ connected to one virtual switch:
– Start mininet without any arguments:
Then in the mininet terminal, run:
h2 iperf -s &
h1 iperf -t 10 -c 10.0.0.2 After iperf finishes, run:
h1 ping -c 3 h2
Question 1: What is the bandwidth and the average delay reported between the two hosts?
Now let’s limit the bandwidth, and increase the delay, and see what happens. Exit out of mininet with ‘quit’.
Start mininet with these arguments:
sudo mn –link tc,bw=10,delay=10ms
Then in the mininet terminal, run iperf:
h2 iperf -s &
h1 iperf -t 10 -c 10.0.0.2
After iperf finishes, run:
h1 ping -c 3 h2
Question 2: What is the bandwidth and the average delay reported between the two hosts?
By default, Mininet hosts start with randomly assigned MAC addresses. Every time the Mininet is created, the MAC addresses change, so correlating traffic with specific hosts can be a challenge. We can use –mac to set MAC and IP addresses to small, unique, easy to read values. This will come in handy in future labs.
Start mininet:
Then in the mininet terminal, run:
h1 ifconfig
Question 3: What is IP address and the MAC address of the host?
Now try the –mac option
– Start mininet with these arguments:
sudo mn –-mac
Then in the mininet terminal, run
h1 ifconfig
Question 4. Now what is the IP address and the MAC address of the host?
Hint: IP address may not change but the MAC address will change to a simpler one.
Code Help
LAB 2 (20 points)
Step 1. Start ipmininet using an example topology for Layer 2 Spanning Tree:
sudo python3 -m ipmininet.examples \
–-topo=spanning_tree_network
Step 2. Type ‘net’ to see what’s connected to what. You’ll see something similar to this:
Q1: Using your favorite drawing program, or just a pencil and paper, draw a network diagram that includes the three hosts (hs1, hs2, hs3) and the three switches (s1, s2, s3). Be sure to show all interconnections between hosts and switches. Label the interfaces.
Step 3: Using ‘ifconfig’ find the MAC address of the three hosts. For example:
hs1 ifconfig
hs2 ifconfig
hs3 ifconfig
Q2: Add the MAC address of each host’s interface to your diagram from #2.
Step 4: This lab uses Linux bridges to implement the ‘switch’. What it is actually doing is implementing three different bridges on a single container. In the mininet cli, s1, s2 and s3 “switches” are actually the same container. But they are then logically separated inside the container as three bridges, also called s1, s2 and s3. It’s the logically separated ones we care about in this lab.
Execute the command:
s1 brctl show
Q3: How many switches/bridges do you see?
Note you could type s2 brctl show and get the same output (reason given above). Step 5: Now execute the commands:
s1 brctl showmacs s1
s1 brctl showmacs s2
s1 brctl showmacs s3
Q4: What do you see? Can you figure out which MAC addresses belong to what devices? Using ‘ifconfig’ find and document where each MAC came from.
Step 6: Run the command:
Q5: This will send some traffic (an ICMP ECHO request) to and from each host. How does this change the output of ‘brctl showmacs’ for all three bridges? Why is this? Explain your answer.
Step 7: Using the mininet command:
s1 brctl showstp s1 s1 brctl showstp s2 s1 brctl showstp s3
Q6: Find which interface in the spanning tree topology is in the blocked state. which interface this is in your diagram above.
Q7: Find which bridge is the spanning tree root and document why it was elected as such.
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Step 8: Start up Wireshark on hs1. At the mininet prompt:
hs1 wireshark &
You should see this pop up on your screen:
Choose the hs1-eth0 interface to dump packets (double click on it). You will start to see packets being captured in the Wireshark interface:
In the top window, pick one of the STP packets (spanning tree protocol).
In the middle window (underneath) start to dissect the packet. In this case there are four constituent parts – Frame, Ethernet, Link Layer and Spanning Tree itself.
Answer these questions about the captured STP packet and show some annotated screen shots to validate your work:
Q8: How many bits on the wire is the total STP packet?
Q9: What is the source MAC address of the STP packet, and what is the destination MAC address? What is special about that destination MAC?
Q10: Dig into the spanning tree portion of the packet capture. Find validation that the STP root you found in the previous lab exercise is correct. Show your work (annotated screen shot) and explain.
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