Teaching Computer
Networking with Mininet
Te-Yuan Huang, Vimalkumar Jeyakumar
Bob Lantz, Brian O'Connor
Nick Feamster
Keith Winstein, Anirudh Sivaraman
Wi-Fi: HHonors, SGC2014
Tutorial Goals
Learn how Mininet (and network emulation in
general) works, and how it can be used in
computer networking courses
Gain hands-on experience using Mininet for a
network lab exercise
Find out what we've learned from using Mininet
in on-campus courses and MOOCs
Tutorial Agenda
1. Introduction to Mininet
presentation, demos, short break
2. Hands-on Lab
presentation, lab, coffee break
3. Teaching with Mininet
presentations, discussion, done!
Teaching Computer
Networking with Mininet
Session 1: Introduction to Mininet
Bob Lantz
Open Networking Laboratory
Introduction to Mininet
Platforms for Network/Systems Teaching
Network Emulator Architecture
Mininet: Basic Usage, CLI, API
Example Demos: Network Security
Conclusion and Questions
Experiential Learning for Networking
"Learning by doing" is memorable and leads
to mastery.
In computer systems courses, this means
building, modifying, using, and experimenting
with working systems.
Networking (and distributed systems) courses
require complicated testbeds including multiple
servers and switches.
Platforms for Network/Systems
Teaching (and Research)
Platform Advantages Disadvantages
Hardware Testbed fast
accurate: "ground truth"
expensive
shared resource?
hard to reconfigure
hard to change
hard to download
Simulator inexpensive, flexible
detailed (or abstract!)
easy to download
virtual time (can be
"faster" than reality)
may require app changes
might not run OS code
detail != accuracy
may not be "believable"
may be slow/non-interactive
Emulator inexpensive, flexible
real code
reasonably accurate
easy to download
fast/interactive usage
slower than hardware
experiments may not fit
possible inaccuracy from
multiplexing
Introduction to Mininet
Platforms for Network/Systems Teaching
Network Emulator Architecture
Mininet: Basic Usage, CLI, API
Example Demos: Network Security
Conclusion and Questions
To start with,
a Very Simple Network
Host
Switch
Host
firefox
httpd
VM Server
Very Simple Network using
Full System Virtualization
ovs-vswitchd
Linux Kernel
openvswitch kernel module
Host VM
cupsd
Linux Kernel
init
bash
firefox
eth0
tap0
eth0
tap1
Host VM
cupsd
Linux Kernel
init
bash
httpd
eth0
10.0.0.1 10.0.0.2
Server (or VM!)
Very Simple Network using
Lightweight Virtualization
ovs-vswitchd
Linux Kernel
openvswitch kernel module
Network Namespace 1
firefox
veth1
eth0
veth2
Network Namespace 2
httpd
eth0eth0
10.0.0.1 10.0.0.2
Root Namespace
Mechanism: Network Namespaces
and Virtual Ethernet Pairs
Network Namespace 1
firefox
veth1
eth0
veth2
Network Namespace 2
httpd
eth0eth0
Software
Switch
virtual Ethernet pairs
10.0.0.1 10.0.0.2
Creating it with Linux
sudo bash
# Create host namespaces
ip netns add h1
ip netns add h2
# Create switch
ovs-vsctl add-br s1
# Create links
ip link add h1-eth0 type veth peer name s1-eth1
ip link add h2-eth0 type veth peer name s1-eth2
ip link show
# Move host ports into namespaces
ip link set h1-eth0 netns h1
ip link set h2-eth0 netns h2
ip netns exec h1 ip link show
ip netns exec h2 ip link show
# Connect switch ports to OVS
ovs-vsctl add-port s1 s1-eth1
ovs-vsctl add-port s1 s1-eth2
ovs-vsctl show
# Set up OpenFlow controller
ovs-vsctl set-controller s1 tcp:127.0.0.1
ovs-controller ptcp: &
ovs-vsctl show
# Configure network
ip netns exec h1 ifconfig h1-eth0 10.1
ip netns exec h1 ifconfig lo up
ip netns exec h2 ifconfig h2-eth0 10.2
ip netns exec h1 ifconfig lo up
ifconfig s1-eth1 up
ifconfig s1-eth2 up
# Test network
ip netns exec h1 ping -c1 10.2
s1
h1
10.0.0.1
h2
10.0.0.2
ctrl’er
Wouldn’t it be great if...
We had a simple command-line tool and/or API
that did this for us automatically?
It allowed us to easily create topologies of
varying size, up to hundreds of nodes, and run
tests on them?
It was already included in Ubuntu?
Introduction to Mininet
Platforms for Network/Systems Teaching
Network Emulator Architecture
Mininet: Basic Usage, CLI, API
Example Demos: Network Security
Conclusion and Questions
Mininet command line tool and CLI
demo
# mn
# mn --topo tree,depth=3,fanout=3 --
link=tc,bw=10
mininet> xterm h1 h2
h1# wireshark &
h2# python -m SimpleHTTPServer 80 &
h1# firefox &
# mn --topo linear,100
# mn --custom custom.py --topo mytopo
Mininet API basics
net = Mininet() # net is a Mininet() object
h1 = net.addHost( 'h1' ) # h1 is a Host() object
h2 = net.addHost( 'h2' ) # h2 is a Host()
s1 = net.addSwitch( 's1' ) # s1 is a Switch() object
c0 = net.addController( 'c0' ) # c0 is a Controller()
net.addLink( h1, s1 ) # creates a Link() object
net.addLink( h2, s1 )
net.start()
h2.cmd( 'python -m SimpleHTTPServer 80 &' )
sleep( 2 )
h1.cmd( 'curl', h2.IP() )
CLI( net )
h2.cmd('kill %python')
net.stop()
s1
h1
10.0.0.1
h2
10.0.0.2
c0
Performance modeling in Mininet
# Use performance-modeling link and host classes
net = Mininet(link=TCLink, host=CPULimitedHost)
# Limit link bandwidth and add delay
net.addLink(h2, s1, bw=10, delay='50ms')
# Limit CPU bandwidth
net.addHost('h1', cpu=.2)
s1
h1
10.0.0.1
20% of CPU
h2
10.0.0.2
controller
10 Mbps, 50 ms
Low-level API: Nodes and Links
h1 = Host( 'h1' )
h2 = Host( 'h2' )
s1 = OVSSwitch( 's1', inNamespace=False )
c0 = Controller( 'c0', inNamespace=False )
Link( h1, s1 )
Link( h2, s1 )
h1.setIP( '10.1/8' )
h2.setIP( '10.2/8' )
c0.start()
s1.start( [ c0 ] )
print h1.cmd( 'ping -c1', h2.IP() )
s1.stop()
c0.stop()
Mid-level API: Network object
net = Mininet()
h1 = net.addHost( 'h1' )
h2 = net.addHost( 'h2' )
s1 = net.addSwitch( 's1' )
c0 = net.addController( 'c0' )
net.addLink( h1, s1 )
net.addLink( h2, s1 )
net.start()
print h1.cmd( 'ping -c1', h2.IP() )
CLI( net )
net.stop()
High-level API: Topology templates
class SingleSwitchTopo( Topo ):
"Single Switch Topology"
def build( self, count=1):
hosts = [ self.addHost( 'h%d' % i )
for i in range( 1, count + 1 ) ]
s1 = self.addSwitch( 's1' )
for h in hosts:
self.addLink( h, s1 )
net = Mininet( topo=SingleSwitchTopo( 3 ) )
net.start()
CLI( net )
net.stop()
more examples and info available at docs.mininet.org
Custom Topology Files
# cat custom.py
from mininet.topo import Topo
class SingleSwitchTopo( Topo ):
"Single Switch Topology"
def build( self, count=1):
hosts = [ self.addHost( 'h%d' % i )
for i in range( 1, count + 1 ) ]
s1 = self.addSwitch( 's1' )
for h in hosts:
self.addLink( h, s1 )
topos = { 'mytopo': SingleSwitchTopo }
# mn --custom custom.py --topo mytopo,3
*** Creating network
*** Adding controller
*** Adding hosts:
h1 h2 h3
Introduction to Mininet
Platforms for Network/Systems Teaching
Network Emulator Architecture
Mininet: Basic Usage, CLI, API
Example Demos: Network Security
Conclusion and Questions
Security Demo #1: DHCP Attack
h1
10.0.0.10
(client/
victim)
Switch
dhcp
10.0.0.50
(good DHCP
server)
evil
10.0.0.66
(malicious
DHCP+DNS+
WWW server)
internet
slow link
(500 ms delay)
Security Demo #2: BGP
More Demos!
MiniEdit
Consoles.py
Cluster prototype
Introduction to Mininet
Platforms for Network/Systems Teaching
Network Emulator Architecture
Mininet: Basic Usage, CLI, API
Example Demos: Network Security
Conclusion and Questions
Conclusion and Questions
Network Emulators can facilitate teaching networking via realistic live
demos, interactive labs and course assignments
- inexpensive, interactive, real apps and OS, reasonably accurate
- downloadable, fast setup
Mininet is a lightweight virtualization/container based emulator
- modest hardware requirements, fast startup, hundreds of nodes
- command line tool, CLI, simple Python API
- SDN as well as Ethernet/IP networking as well as SD
- install using VM, Ubuntu package, or source
mininet.org: Tutorials, walkthroughs, API documentation and examples
teaching.mininet.org: Mininet-based course assignments and labs
open source: hosted on github, permissive BSD license
Next up: short break, then hands-on lab!
Tutorial Agenda
1. Introduction to Mininet
presentation, demos, short break
2. Hands-on Lab
presentation, lab, coffee break
3. Teaching with Mininet
presentations, discussion, done!
Backup/Supplementary
Slides
Mininet is a Network Emulator
In this talk, emulation (or running on an
emulator) means running unmodified code
interactively on virtual hardware on a regular
PC, providing convenience and realism at low
cost – with some limitations (e.g. speed, detail.)
This is in contrast to running on a hardware
testbed (fast, accurate, expensive/shared) or a
simulator (cheap, detailed, but perhaps slow
and requiring code modifications.)
Context: Platforms for Network
Experimentation and Development
Container-based emulators: CORE, virtual
Emulab, Trellis, Imunes, even ns-3 (in
emulation mode), Mininet
VM-based emulators: DieCast
UML-based emulators: NetKit
Simulators: ns-3, OPNET
Testbeds: Emulab, GENI, PlanetLab, ORBIT
All of these are fine, but we think Emulators are
particularly useful! Why? Because...
Apps move seamlessly to/from hardware
Host
Switch
Controller
Switch
Switch
Host
Host
Hardware Network
SDN App
Emulated Network
App
App
# mn
> h1 ping h2
Controller
SDN App
Appendix: Mininet
Subclassing for Fun and
Profit
Bob Lantz, Brian O'Connor
Classes in Mininet
Example
class Host( Node ):
"A host is simply a Node"
pass
What do you want to customize?
class Node( object ):
def config( self, mac=None, ip=None,
defaultRoute=None, lo='up', **_params ):
# If we were overriding this method, we would call
# the superclass config method here as follows:
# r = Parent.config( **_params )
r = {}
self.setParam( r, 'setMAC', mac=mac )
self.setParam( r, 'setIP', ip=ip )
self.setParam( r, 'setDefaultRoute', defaultRoute=defaultRoute )
self.cmd( 'ifconfig lo ' + lo )
return r
Customizing Host()
class VLANHost( Host ):
def config( self, vlan=100, **params ):
"""Configure VLANHost according to (optional) parameters:
vlan: VLAN ID for default interface"""
r = super( Host, self ).config( **params )
intf = self.defaultIntf()
self.cmd( 'ifconfig %s inet 0' % intf ) # remove IP from default, "physical" interface
self.cmd( 'vconfig add %s %d' % ( intf, vlan ) ) # create VLAN interface
self.cmd( 'ifconfig %s.%d inet %s' % ( intf, vlan, params['ip'] ) ) # assign the host's IP to
the VLAN interface
# to maintain CLI compatibility
newName = '%s.%d' % ( intf, vlan ) # update the intf name and host's intf map
intf.name = newName # update the (Mininet) interface to refer to VLAN interface name
self.nameToIntf[ newName ] = intf # add VLAN interface to host's name to intf map
return r
hosts = { 'vlan': VLANHost }
Using Custom Hosts
In Python:
def run( vlan ):
# vlan (type: int): VLAN ID to be used by all hosts
host = partial( VLANHost, vlan=vlan )
# Start a basic network using our VLANHost
topo = SingleSwitchTopo( k=2 )
net = Mininet( host=host, topo=topo )
net.start()
CLI( net )
net.stop()
From the CLI:
sudo mn --custom vlanhost.py --host vlan,vlan=1000
Customizing Switch()
class LinuxBridge( Switch ):
"Linux Bridge"
prio = 0
def __init__( self, name, stp=True, **kwargs ):
self.stp = stp
Switch.__init__( self, name, **kwargs ) # BL doesn’t care about multiple inheritance
def start( self, controllers ):
self.cmd( 'ifconfig', self, 'down' )
self.cmd( 'brctl delbr', self )
self.cmd( 'brctl addbr', self )
if self.stp:
self.cmd( 'brctl setbridgeprio', self.prio )
self.cmd( 'brctl stp', self, 'on' )
LinuxBridge.prio += 1
for i in self.intfList():
if self.name in i.name:
self.cmd( 'brctl addif', self, i )
self.cmd( 'ifconfig', self, 'up' )
def stop( self ):
self.cmd( 'ifconfig', self, 'down' )
self.cmd( 'brctl delbr', self )
switches = { 'lxbr': LinuxBridge }
Customizing Switch()
demo
openflow@ubuntu13:~$ sudo mn --custom torus3.py --switch lxbr --topo torus,3,3
…
mininet> sh brctl showstp s0x0
…
Customizing Switch()
c0 = Controller( 'c0', port=6633 )
c1 = Controller( 'c1', port=6634 )
c2 = RemoteController( 'c2', ip='127.0.0.1' )
cmap = { 's1': c0, 's2': c1, 's3': c2 }
class MultiSwitch( OVSSwitch ):
"Custom Switch() subclass that connects to different controllers"
def start( self, controllers ):
return OVSSwitch.start( self, [ cmap[ self.name ] ] )
topo = TreeTopo( depth=2, fanout=2 )
net = Mininet( topo=topo, switch=MultiSwitch )
for c in [ c0, c1 ]:
net.addController(c)
net.start()
CLI( net )
net.stop()
DEMO: controllers.py
Customizing Controller()
from mininet.node import Controller
from os import environ
POXDIR = environ[ 'HOME' ] + '/pox'
class POX( Controller ):
def __init__( self, name, cdir=POXDIR,
command='python pox.py',
cargs=( 'openflow.of_01 --port=%s '
'forwarding.l2_learning' ),
**kwargs ):
Controller.__init__( self, name, cdir=cdir, command=command, cargs=cargs, **kwargs )
controllers={ 'pox': POX }
Customizing Controller()
from mininet.node import Controller
from os import environ
from functools import partial
POXDIR = environ[ 'HOME' ] + '/pox'
POX = partial( Controller, cdir=POXDIR,
command='python pox.py',
cargs=( 'openflow.of_01 --port=%s '
'forwarding.l2_learning' ) )
controllers = { 'pox': POX }
