Mininet Walkthrough
جولای 14, 2019
آموزش شبیه سازی با نرم افزار r
جولای 14, 2019

مقدمات mininet

تحقیق پیاده سازی و مانیتورینگ شبکه SDN با امولاتور Mininet

Introduction to Mininet

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Lab Exercise 3 (part A) Introduction to Mininet
Learn the basic commands in Mininet
Learn how to create basic network topologies in Mininet
Learn Mininet API
This exercise forms the first part of lab exercise 3. The second part (part B) will be part of next
week’s lab. Both parts together will comprise 15 marks. Only selected exercises will be marked.
However, students must submit answers for all exercises.
Before your scheduled lab next week. So you get one week to work on this lab. For example, if you
go to the Monday 12 noon lab, then your submission is due before 12 noon on the following
Monday. You can submit as many times as you wish before the deadline. A later submission will
override the earlier submission, so make sure you submit the correct file. Do not leave until the last
moment to submit, as there may be technical or communications error and you will not have time to
rectify it.
Late Penalty:
Late penalty will be applied as follows:
1 day after deadline: 20% reduction
2 days after deadline: 40% reduction
3 days after deadline: 60% reduction
4 or more days late: NOT accepted
Note that the above penalty is applied to your final mark. For example, if you submit your lab work 2
days late and your score on the lab is 8, then your final mark will be 8-3.2 (40% penalty) = 4.8.
Submission Instructions:
Submit a PDF document lab3a.pdf with answers to all questions for all exercises. Include all
supporting documents such as topology files for Questions 5 and 6(*.py). Create a tar archive of all
files called
lab3a.tar. Submit the archive using give. Click on the submission link at the top of the
page. Max file size for submission is 3MB.
Original Work Only:
You are strongly encouraged to discuss the questions with other students in your lab. However, each
student must submit his or her own work. You may refer to the reference material and also conduct
your own research to answer the questions.

Part 1: Basic Commands in Mininet
In the first step, we start a simple network topology by running the following command:
The above command creates the default topology in Mininet (known as the
minimal topology),
which includes one OpenFlow
1 kernel switch connected to two hosts, plus the OpenFlow reference.
This topology could also be mentioned on the command line using option —
topo=minimal with the
mn command. Once you run the above command, all four entities (two hosts, one switch, and one
controller) are running in the VM and the Mininet CLI comes up. You can run the
help command to
see the list of commands in the CLI. In the rest of this section, you will practice the basic commands
in Mininet.
Display nodes:
For more detailed information about the nodes in the network, use dump.
Display topology:
Simple commands within a node:
If the first string typed into the Mininet CLI is a host, switch or controller name, the corresponding
command is executed on that node. For example, run the following command on host
h1 to show its
network interfaces.
OpenFlow is communication protocol between switches and controllers. We do not need to know the details
of the OpenFlow protocol in this course.
Notation: In the examples below, we have used the $ sign to represent Linux commands that
should be typed at the shell prompt,
mininet> to show Mininet commands that should be
typed at Mininet’s CLI (command line interface), and
# to show Linux commands that are typed
at a root shell prompt. In each case, you should only type the name of the command and then
press return. The actual prompt may look very different on your computer (e.g. it may contain
the computer’s hostname, or your username, or the current directory name). The commands
you are supposed to type are in this bold font.
$ sudo mn
mininet> nodes
mininet> net
mininet> h1 ifconfig -a
In the above command, you can replace
h1 with s1 to see the details of the switch’s interfaces. Also,
for a list of processes in a host you can run
h1 ps –a.
Note that a switch is a layer 2 packet switch (also known as a bridge). We will examine switches in
details when we study about the link layer.
Question 1: Draw the Mininet minimal topology and include the IP and MAC addresses for hosts and
the switch. To which switch ports are the hosts and controller connected?
Test connectivity between hosts:
In order to ping host 1 from host 2, run the following command:
Question 2: Examine the ping time for all five tries in the above command. What is the ping time for
each try?
Question 3: You should see that the ping time for the first try is larger than the next tries. How do
you explain this observation?
A simple way to test the connectivity of all nodes in the Mininet CLI is to run the
pingall command,
which does an all-pairs
XTerm display
To display an xterm for host h1, run the following command. This will be useful to run commands
within a host or switch.
Python Interpreter
If the first part of a command in Mininet is py, then the CLI interprets the command as a Python
command. This helps you to manipulate the network objects, such as hosts, switches, and
controllers, using the CLI. Here is an example which displays the IP address of host
Exit and clean up
For exiting from the Mininet CLI, run command exit. It is strongly recommended to clean up after
exiting by running command
sudo mn –c.
mininet> h1 ping –c5 h2
mininet> xterm h1
mininet> py h1.IP()
Part 2: Custom Topologies
Mininet supports a simple Python API to create custom network topologies. You can create your
custom topology by writing a few lines of Python code. For example, Figure 1 shows a topology with
two switches and four hosts. Figure 2 implements the topology using the Mininet Python API. The
code consists of a class, named MyFirstTopo which extends the Topo class provided by the API. We
suggest that you SSH into your mininet VM so that you can use a GUI text editor such as gedit or
emacs (see instructions in the Mininet Introduction document). Save the source code in a file,
named in your (mounted) CSE home directory. You can download the source code
from here: Change the working directory to your CSE home directory and type:
Question 4: Draw Figure 1 and label the IP and MAC address for the hosts. Also label the interface
names and MAC address of the switch ports that are connected to the hosts.

Switch1(s1) Switch2(s2)

Host 1 (h1)
Host 2 (h2)
Host 3 (h3)
Host 4 (h4)
Figure 1 A sample network topology (
Figure 2 Source code for the custom topology presented in Figure 1.
mininet> sudo mn –custom –topo myfirsttopo
1. from mininet.topo import Topo
class MyFirstTopo( Topo ):
4. “Simple topology example.”
5. def __init__( self ):
6. “Create custom topo.”
7. # Initialize topology
8. Topo.__init__( self )
9. # Add hosts and switches
10. h1 = self.addHost( ‘h1’ )
11. h2 = self.addHost( ‘h2’ )
12. h3 = self.addHost( ‘h3’ )
13. h4 = self.addHost( ‘h4’ )
14. leftSwitch = self.addSwitch( ‘s1’ )
15. rightSwitch = self.addSwitch( ‘s2’ )
16. # Add links
17. self.addLink( h1, leftSwitch )
18. self.addLink( h2, leftSwitch )
19. self.addLink( leftSwitch, rightSwitch )
20. self.addLink( rightSwitch, h3 )
21. self.addLink( rightSwitch, h4 )
topos = { ‘myfirsttopo’: ( lambda: MyFirstTopo() ) }
If you want to run a quick test without entering the CLI, you can use option
–test in Mininet, as
Now assume that we want to accomplish the following:
1. Create the topology shown in Figure 1
2. Start the network
3. Show the detailed connectivity of all nodes in the network
4. Test the connectivity by pinging all nodes
We can automate this sequence of operations by writing a Python script. This helps us to automate
network experiments. To this end, we extend the previous source code, as shown in Figure 3.
Download the source code from here:
Figure 3 Source code for an experiment on the custom topology.
mininet> sudo mn –custom –topo myfirsttopo –test pingall
1. #!/usr/bin/python
from mininet.topo import Topo
4. from import Mininet
5. from mininet.util import dumpNodeConnections
6. from mininet.log import setLogLevel
class MyFirstTopo( Topo ):
9. “Simple topology example.”
10. def __init__( self ):
11. “Create custom topo.”
12. # Initialize topology
13. Topo.__init__( self )
14. # Add hosts and switches
15. h1 = self.addHost( ‘h1’ )
16. h2 = self.addHost( ‘h2’ )
17. h3 = self.addHost( ‘h3’ )
18. h4 = self.addHost( ‘h4’ )
19. leftSwitch = self.addSwitch( ‘s1’ )
20. rightSwitch = self.addSwitch( ‘s2’ )
21. # Add links
22. self.addLink( h1, leftSwitch )
23. self.addLink( h2, leftSwitch )
24. self.addLink( leftSwitch, rightSwitch )
25. self.addLink( rightSwitch, h3 )
26. self.addLink( rightSwitch, h4 )
def runExperiment():
29. “Create and test a simple experiment”
30. topo = MyFirstTopo( )
31. net = Mininet(topo)
32. net.start()
33. print “Dumping host connections”
34. dumpNodeConnections(net.hosts)
35. print “Testing network connectivity”
36. net.pingAll()
37. net.stop()
if __name__ == ‘__main__’:
40. # Tell mininet to print useful information
41. setLogLevel(‘info’)
42. runExperiment()
Now download the source code and save it in a file named and run the following
Remember to clean up (sudo mn –c) and also to save your work in your CSE home directory before
moving forward.
Part 3: Mininet Python Classes
The Mininet Python API consists of a number of Python classes, such as Topo, Mininet, Host, Switch,
Link and their subclasses. The API is built at three primary levels which provide different level of
abstractions for customising the network topologies. Here is a brief description of the levels:
Low-level API: This API includes the base node and link classes such as Host, Switch and Link.
You can directly instantiate some objects from these classes to create a network.
Mid-level API: This API consists of the Mininet class which provides a number of methods,
such as addHost(), addSwitch(), and addLink(), for creating a network.
High-level API: This API consists of the Topo class, which provides the ability to create
reusable, parameterised topology templates. These templates can be passed to the
command (via the –custom option as in Part 2 above) and used from the command line.
Figure 2 and Figure 3 are two examples that show how to use the high-level API. As you can see, the
high-level API provides an object-oriented framework by presenting the
Topo class. Figure 4 shows
how to use the low-level API for creating the custom topology presented in Figure 1. Download the
source code from here: Observe that, with the low-level API we create all
the objects and connect the topology manually. You can test this code by typing the following:
You can find the detailed documentation of all classes provided in the Mininet Python API in
mininet> sudo python
mininet> sudo python
Figure 4 Source code for the topology presented in Figure 1 using low-level API.
Remember to clean up (sudo mn –c) and also to save your work in your CSE home directory before
moving forward.
Part 4: Simple Tree Topology
Many data centres use a tree-like network topology. End-hosts (i.e. servers) connect to top-of-rack
switches, called
edge switches and form the leaves of the tree; one or more core switches form the
root of the tree; and one or more
aggregation switches form the intermediate nodes of the tree. In
simple tree topology, there is only one core switch connected to 𝑛 aggregation switches; each
aggregation switch is connected to
𝑛 edge switches; each edges switches is connected to 𝑛 hosts
(servers). Figure 5 shows a simple tree topology where n
1. #!/usr/bin/python
from mininet.node import Host,OVSSwitch,Controller
4. from import Link
h1 = Host( ‘h1’ )
7. h2 = Host( ‘h2’ )
8. h3 = Host( ‘h3’ )
9. h4 = Host( ‘h4’ )
10. s1 = OVSSwitch( ‘s1’, inNamespace=False )
11. s2 = OVSSwitch( ‘s2’, inNamespace=False )
12. c0 = Controller( ‘c0’, inNamespace=False )
13. Link( h1, s1 )
14. Link( h2, s1 )
15. Link( h3, s2 )
16. Link( h4, s2 )
17. Link( s1, s2 )
18. h1.setIP( ‘’ )
19. h2.setIP( ‘’ )
20. h3.setIP( ‘’ )
21. h4.setIP( ‘’ )
22. c0.start()
23. s1.start( [ c0 ] )
24. s2.start( [ c0 ] )
25. print h1.IP
26. print h2.IP
27. print h3.IP
28. print h4.IP
29. print ‘Pinging …’
30. print h1.cmd( ‘ping -c3 ‘, h2.IP() )
31. print h1.cmd( ‘ping -c3 ‘, h3.IP() )
32. s1.stop()
33. s2.stop()
34. c0.stop()
Figure 5 Simple-tree topology with
𝑛 = 2.
Question 5: Write a Python program to use the high-level API and create a simple-tree data centre
topology. You must follow the naming system as shown in Figure 6. The program gets the value of
as an input. You must organise all the source code in a single source file, name it, and include this file in the submission archive.
Question 6: Repeat the previous question but now use the low-level API. You must organise all the
source code in a single source file, name it, and include this file in the
submission archive.
Question 7: Use your program (either high-level or low-level) to create a simple-tree with
𝑛 = 2, as
shown in Figure 5. Check the connectivity of all nodes in the network and write your observations.
Now stop the core switch using command
switch c1 stop, check the connectivity of all hosts and
report your observations. How do you explain your findings? Write up your answer in the report.
Part 5: Useful Resources
Introduction to Mininet:
Mininet Walkthrough:
Mininet Python API Reference Manual:

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