SDN and Mininet

Where will it be used?

Definitely here

image source: backblaze.com

Very likely here

image source: computerbase.de

Maybe here

image source: heise.de

Not here

image source: avm.de

So … should I care as an end user?

-

No

What are the differences to classical networking?

image source: engeniustech.com

• Operate on the ethernet layer
• Nodes form a broadcast group
• Node addresses are learned
• Addresses don't form a hierarchy

image source: networkscreen.com

• Broadcast groups don't scale
• Use hierarchically asigned addresses
• Routing table has to come from somewhere

• Do not know anything about a network by default
• Can be fed rules proactively or reactively
• Relies on a SDN controller

Data forwarding and rule-making are part of the same device

image source: David Mahler via Youtube

Data forwarding and rule-making are decoupled

image source: David Mahler via Youtube

How are SDN controllers written?

• … is a protocol on top of TCP
• can be implemented whenerver TCP is available
• Python, Java, Ruby, C … on Linux, BSD, Windows …

SDN controller frameworks simplify writing controllers

1 from ryu.base import app_manager
2 
3 class L2Switch(app_manager.RyuApp):
4     def __init__(self, *args, **kwargs):
5         super(L2Switch, self).__init__(*args, **kwargs)

source: http://ryu.readthedocs.io

How are SDN controllers tested?

Mininet

Mininet is a python-based network simulation tool

Using mininet one can test …

• … SDN controllers
• … the performance of distributed computer systems
• … fault behaviours in networks
• … application behaviour in slow/intermittend networks

and more

(fujitsu.com)

Mininet uses container based virtualization to emulate network hosts

Containers are an alternative to classical full-OS virtualization

Applications in a Container are isolated from the other containers by the operating system kernel

Pros:

• Lower ressource utilization
• Faster startup

Cons

• Less secure isolation
• Highly operation system dependant

Mininet uses the Linux container virtualization features
⇒ Only runs on Linux

It can be installed using …

• … a pre-made virtual machine image
• … from source on a linux system
• … using a distribution packet

Mininet workflow

The virtual machine image provided by the mininet community has all of the required tool for running mininet pre-installed and pre-configured.

It is based on the Ubuntu Linux distribution so installing additional software is relatively easy.

…

The network topology is configured as a python script that is read by mininet.

It sets up the hosts to simulate and the forwarding devices connecting these hosts.

…

The openflow controller is responsible for analyzing packets entering the forwarding devices and for installing forwarding rules into the device.

Once the openflow controller is started is listens on a TCP port for connections from forwarding devices.

On the previous slide mininet was instructed to run the network topology written earlier and to connect to the custom openflow controller.

The example simulates three hosts connected to a single central switch.

In order to validate the behaviour of the openflow controller the packets flowing into and out of the simulated hosts is monitored.

This is done using the wireshark network analyzer.

The simulated hosts in the mininet topology are implemented using Linux container virtualization.

Any command available for execution on the mininet VM can also be used in the simulated hosts.

In the example at hand the ip addr command is used on the first host to find its IP address and the ping command is used to send packets from the second host to the first one.

If the test was successful the wireshark instances should show packets flowing between the two hosts.

The previous slide shows the setup I used while developing my openflow controllers.

The tools used are (in clockwise order): Text editor for editing the controllers, Wireshark network analyzer, documentation/source code of the framework I used, debug output of the controller, mininet shell.

What I implemented so far:

• An ethernet switch
• An IPv4 router