Assignment 4: Software Defined Networking

CS640 Fall 2019

Due: Friday, November 22 at 11:59pm


For this project you will implement two control application for a software defined network (SDN). A layer-3 routing application will install rules in SDN switches to forward traffic to hosts using the shortest, valid path through the network. A distributed load balancer application will redirect new TCP connections to hosts in a round-robin order.

Part 1: Getting Started

Part 2: Layer-3 Routing Application

Part 3: Distributed Load Balancer Application

Submission Instructions

Please find the FAQs of this assignment in the link

Learning Objectives

After completing this programming assignment, students should be able to:

Part 1: Getting Started

Your SDN applications will be written in Java and run atop the Floodlight OpenFlow controller. You will use Mininet to emulate a variety of network topologies consisting of OpenFlow switches and hosts. You should continue to use your assigned Mininet virtual machine (VM) for this project.

Preparing Your Environment

Before beginning this project, there are some additional steps you need to complete to prepare your VM:

  1. Install required packages

sudo apt-get update
sudo apt-get install -y curl traceroute ant openjdk-7-jdk git iputils-arping

  1. Download Floodlight:
    cd ~
            git clone
  2. Download the starter code:

cd ~
tar xzvf assign4.tgz

  1. Symlink Floodlight
            cd ~/assign4/
            ln -s ../floodlight-plus
  2. Patch Floodlight
            cd ~/assign4/floodlight-plus
            patch -p1 < ~/assign4/floodlight.patch
  3. Install new version of Mininet and patch it

cd ~/assign4


If you want to use Eclipse (on a machine other than your VM) for development, you should do the following:

  1. cd floodlight-plus
    ant eclipse
  2. Open Eclipse and create a new workspace. Do not choose the floodlight-plus or assign4 folders as the location for your workspace.
  3. Select File → Import → General → Existing Projects into Workspace. Click Next.
  4. From Select root directory click Browse. Select the parent folder containing your floodlight-plus and assign4 folders.
  5. Check the boxes for floodlight-plus and assign4. Click Finish.
  6. Exclude the src/test/java folder from the build path:
  1. Right click on this folder in the Project Explorer pane.
  2. Select Build Path →Remove from Build Path.
  1. Add the floodlight-plus project to the build path of assign4:
  1. Right click assign4 in the Project Explorer pane.
  2. Select Build Path →Configure Build Path.
  3. Under the Projects tab; click Add.
  4. Check the floodlight-plus project; click OK.

Running Your Control Applications

  1. Compile Floodlight and your applications:

  cd ~/assign4/

This will produce a jar file FloodlightWithApps.jar that includes the compiled code for Floodlight and your SDN applications.

  1. Start Floodlight and your SDN applications:
      java -jar FloodlightWithApps.jar -cf l3routing.prop
    The above command will start Floodlight and only your layer-3 routing application. You can start both your layer-3 routing and load balancer applications by using
    loadbalancer.prop for the -cf (configuration file) argument.

When Floodlight starts, you should see output like the following:

19:15:37.239 INFO [n.f.c.m.FloodlightModuleLoader:main] Loading modules from file l3routing.prop

19:15:37.666 INFO [n.f.c.i.Controller:main] Controller role set to MASTER

19:15:37.676 INFO [n.f.c.i.Controller:main] Flush switches on reconnect -- Disabled

19:15:37.697 INFO [ArpServer:main] Initializing ArpServer...

19:15:37.697 INFO [L3Routing:main] Initializing L3Routing...

19:15:38.835 INFO [n.f.l.i.LinkDiscoveryManager:main] Setting autoportfast feature to OFF

19:15:38.891 INFO [ArpServer:main] Starting ArpServer...

19:15:38.892 INFO [L3Routing:main] Starting L3Routing...

19:15:39.122 INFO [o.s.s.i.c.FallbackCCProvider:main] Cluster not yet configured; using fallback local configuration

19:15:39.122 INFO [o.s.s.i.SyncManager:main] [32767] Updating sync configuration ClusterConfig [allNodes={32767=Node [hostname=localhost, port=6642, nodeId=32767, domainId=32767]}, authScheme=NO_AUTH, keyStorePath=null, keyStorePassword is unset]

19:15:39.185 INFO [o.s.s.i.r.RPCService:main] Listening for internal floodlight RPC on localhost/

19:15:39.421 INFO [n.f.c.i.Controller:main] Listening for switch connections on

Keep the terminal with Floodlight open, as you will need to see the output for debugging. Use another terminal for the next step. Now is a time to use screen. You can install screen in your VM by running: sudo apt-get install screen.

  1. Start Mininet:
      sudo ./ single,3
    The above command will create a topology with a single SDN switch (
    s1) and three hosts (h1 - h3) directly connected to the switch:

    You can change the number of hosts by changing the numeric value included in the arguments to the script. You can also start Mininet with six other topologies:

Once mininet has started, you should see Floodlight produce output like the following:

11:04:44.960 INFO [n.f.c.i.OFChannelHandler:New I/O server worker #2-1] New switch connection from /

11:04:44.999 INFO [n.f.c.i.OFChannelHandler:New I/O server worker #2-1] Disconnected switch [/ DPID[?]]

11:04:46.278 INFO [n.f.c.i.OFChannelHandler:New I/O server worker #2-2] New switch connection from /

11:04:46.355 INFO [n.f.c.i.OFChannelHandler:New I/O server worker #2-2] Switch OFSwitchBase [/ DPID[00:00:00:00:00:00:00:01]] bound to class class net.floodlightcontroller.core.internal.OFSwitchImpl, writeThrottle=false, description OFDescriptionStatistics [Vendor: Nicira, Inc., Model: Open vSwitch, Make: None, Version: 2.0.1, S/N: None]

11:04:46.364 INFO [n.f.c.OFSwitchBase:New I/O server worker #2-2] Clearing all flows on switch OFSwitchBase [/ DPID[00:00:00:00:00:00:00:01]]

11:04:46.377 WARN [n.f.c.i.C.s.notification:main] Switch 00:00:00:00:00:00:00:01 connected.

11:04:46.383 INFO [L3Routing:main] Switch s1 added

11:04:46.432 INFO [L3Routing:Topology Updates] Link s1:0 -> host updated

11:04:46.484 INFO [L3Routing:Topology Updates] Link s1:2 -> host updated

11:04:46.489 WARN [n.f.c.i.C.s.notification:main] Switch 00:00:00:00:00:00:00:01 port s1-eth1 changed: UP

11:04:46.585 INFO [L3Routing:Topology Updates] Link s1:1 -> host updated

  1. You can now run commands (e.g., ping) in mininet like you did for the previous assignments. However, until you complete Part 2, no packets will be forwarded.

You should always start Floodlight and your SDN applications before starting mininet. Also, we recommend that you restart Floodlight and your SDN applications whenever you restart mininet.


If you have questions about SDN, OpenFlow, or Floodlight you may want to consult:

Part 2: Layer-3 Routing Application


In Assignment 3, you wrote a router control plane that used RIP to construct a route table. The route table was then used by your router’s data plane to determine where (i.e., out which interface) a packet should be forwarded.

Your first SDN application will also construct route tables. However, rather than exchanging RIP messages between routers, your application will construct route tables based on a global view of the network topology. The appropriate route table will be installed in each SDN switch by your application, and each SDN switch will forward packets according to the installed route table.

It is important to note that SDN switches do not directly support the route table structure used in the last programming assignment. Rather, SDN switches use a more general flow table structure, which can accommodate route tables (used in traditional layer-3 routers), MAC learning tables (used in traditional layer-2 switches), and many other constructs. Each entry, or rule, in a flow table has match criteria that defines (on the basis of fields in Ethernet, IP, TCP, UDP, and other headers) which packets the rule applies to. Each entry also has one or more instructions/actions which should be taken for each packet that matches the rule.

Your layer-3 routing application will install entries that match packets based on their destination IP address (and Ethernet type), and execute an output action to send the packet out a specific port on the SDN switch.

(You’ll use other match criteria and additional instructions/actions for the other SDN application you write, which is described in Part 3.) The match criteria serves the same purpose as the destination and mask fields in a traditional route table, and the output action servers the same purpose as the interface field in a traditional route table. There is no concept of a gateway in SDN flow tables, but that’s okay—your router only used the gateway to determine how to rewrite a packet’s destination MAC address to ensure correct layer-2 forwarding, and we aren’t using traditional layer-2 forwarding in SDN.

Code Overview

The code for your layer-3 routing application will reside in in the edu.wisc.cs.sdn.apps.l3routing package. The file we provided already contains code to:

We have also provided code in the edu.wisc.cs.sdn.apps.utils package for:


You need to complete the TODOs in to install and remove flow table entries from SDN switches such that traffic is forwarded to a host using the shortest path. Note that Floodlight creates only one instance (i.e., object) of the L3Routing class; this instances handles all switches.

Computing Shortest Paths

You should use the Bellman-Ford algorithm to compute the shortest paths to reach a host h from every other host h’ ∈ H, h ≠ h’ (H is the set of all hosts). You can use the getHosts(), getSwitches(), and getLinks() methods to get the topology information that you need to provide as input to the Bellman-Ford algorithm. (Note: You can use other all pair shortest path algorithms as well)

There will be two link objects between pairs of switches, one in each direction. Due to the way links are discovered, there may be a short period of time (tens of milliseconds) where the controller has a link object only in one direction. If you have a link object in one direction, you can assume the physical link is bidirectional.

When a host joins the network, both the deviceAdded(...) and linkDiscoveryUpdate(...) event handlers will be called. There are no guarantees on which order these event handlers are called.  Thus, a host may be added but we may not yet know which switch it is linked to. The isAttachedToSwitch() method in the Host class will return true if we know the switch to which a host is connected, otherwise it will return false. If the method returns false, then you do not need to install any rules to route traffic to this host.

You can assume the following will always hold true in the network:

Installing Rules

Once you have determined the shortest path to reach host h from h’, you must install a rule in the flow table in every switch in the path. The rule should match IP packets (i.e., Ethernet type is IPv4) whose destination IP is the IP address assigned to host h. You can specify this in Floodlight by creating a new OFMatch object and calling the set methods for the appropriate fields; you must set the Ethernet Type before you set the destination IP. The rule’s action should be to output packets on the appropriate port in order to reach the next switch in the path. You can specify this in Floodlight by creating an OFInstructionApplyActions object whose set of actions consists of a single OFActionOutput object with the appropriate port number.

SDN switches have multiple flow tables—we discuss this more in Part 3. For now, you should install rules in the table specified in the table class variable in the L3Routing class. Also, your rules should never timeout and have a default priority (both defined as constants in the SwitchCommands class).

Testing and Debugging

You should test your code by sending traffic between various hosts in the network topology—mininet’s built-in pingall command is very useful for this.

To help you debug, you can view the contents of an SDN switch’s flow tables by running the following command in your mininet VM (not in mininet itself):

sudo ovs-ofctl -O OpenFlow13 dump-flows s1

This will output the contents of s1’s flow tables. Change the last argument to output the flow tables from a different switch.

Triggering Event Handlers

Part 3: Distributed Load Balancer Application


Networks employ load balancing to distribute client requests among a collection of hosts running a specific service (e.g., a web server).

A hardware load balancer is placed in the network and configured with an IP address (e.g., and a set of hosts among which it should distribute requests (e.g., and Clients wanting to communicate with a service (e.g., a web server) running on those hosts are provided with the IP address of the load balancer, not the IP address of a specific host. Clients initiate a TCP connection to the IP address of the load balancer ( and the TCP port associated with the service (e.g., port 80).

For each new TCP connection, the load balancer selects one of the specified hosts (usually in round robin order). The load balancer maintains a mapping of active connections—identified by the client’s IP and TCP port—to the assigned hosts.

For all packets sent from clients to the load balancer, the load balancer rewrites the destination IP and MAC addresses to the IP and MAC addresses of the selected host. The mapping information stored by the load balancer is used to determine the appropriate host IP and MAC addresses that should be written into a packet arriving from a client. For all packets sent from servers to clients, the load balancer rewrites the source IP and MAC addresses to the IP and MAC addresses of the load balancer.

Your second SDN application will implement the same functionality as a set of hardware load balancers. Your application will be provided with a list of virtual IPs and a set of hosts among which connections to the virtual IPs should be load balanced. (We use the term virtual IP because the IP address is not actually assigned to any node in the network.) When clients initiate TCP connections with a specific virtual IP, SDN switches will send the TCP SYN packet to the SDN controller. Your SDN application will select a host from a pre-defined set, and install rules in an SDN switch to rewrite the IP and MAC addresses of packets associated with the connection. You will also instruct the SDN switch to match the modified packets against the flow rules installed by your layer-3 routing application and apply the appropriate actions (i.e., send the packets out the appropriate ports).

Code Overview

The code for your load balancer application will reside in in the edu.wisc.cs.sdn.apps.loadbalancer package. The file we provided already contains code to:

The LoadBalancerInstance class represents a single distributed load balancer. (We use the term distributed because the load balancing is performed at many switches, rather than at a single hardware load balancer.) Each load balancer instance has a virtual IP address, virtual MAC address, and set of hosts among which TCP connections should be distributed. The instances class variable in the LoadBalancer class maps a virtual IP address to a specific load balancer instance.


You need to complete the TODOs in to:

Connection-specific rules should match packets on the basis of Ethernet type, source IP address, destination IP address, protocol, TCP source port, and TCP destination port. Connection-specific rules should take precedence over the rules that send TCP packets to the controller, otherwise every TCP packet would be sent to the controller. Therefore, these rules should have a higher priority than the rules installed when a switch joins the network.  Also, we want connection-specific rules to be removed when a TCP connection ends, so connection-specific rules should have an idle timeout of 20 seconds.

Multiple Tables

Your load balancer application should work in tandem with your layer-3 routing application. To achieve this, you will need to leverage the multiple tables feature of OpenFlow switches. When packets first arrive at an OpenFlow switch, they are matched against the rules in table 0. The actions for these rules can specify that the packets be modified, output, sent to the controller, and/or matched against the rules in a different table.

Your load balancer application should install rules in the table specified in the table class variable in the LoadBalancer class—set to table 0 in the loadbalancer.prop configuration file. The connection-specific rules that modify IP and MAC addresses should include an instruction to match the modified packets against the rules installed by your layer-3 routing application. Since your layer-3 routing application will install rules in the table class variable in the L3Routing class, this instruction should direct packets to the table defined in this class variable. The modified packet will then be matched against these rules and forwarded out the appropriate port.

All packets which are not TCP packets destined for a virtual IP, or packets associated with a connection that has already been assigned to a specific host, should be send directly the table used by your layer-3 routing application.

Sending ARP Packets

When a client wants to initiate a connection with the virtual IP, it will need to determine the MAC address associated with the virtual IP using ARP.  The client does not know the IP is virtual, and since it’s not actually assigned to any host, your SDN application must take responsibility for replying to these requests.

You can construct an ARP reply packet using the classes in the net.floodlightcontroller.packet package. You can use the sendPacket(...) method in the SwitchCommands class to send the packet.

Rule Instructions/Actions

When a rule should send a packet to the controller, the rule should include an OFInstructionApplyActions whose set of actions consists of a single OFActionOutput with OFPort.OFPP_CONTROLLER as the port number.

When a rule should rewrite the destination IP and MAC addresses of a packet, the rule should include an OFInstructionApplyActions whose set of actions consists of:

The actions for rewriting the source IP and MAC addresses of a packet are similar.

When a packet should be processed by the SDN switch based on the rules installed by your layer-3 routing application, a rule should include an OFInstructionGotoTable whose table number is the value specified in the table class variable in the L3Routing class.

Testing and Debugging

You should test your code by issuing web requests (using curl) from a client host to the virtual IPs.

You can add or remove virtual IPs and hosts by modifying the loadbalancer.prop file.

To see which packets a host is sending/recieving run:

tcpdump -v -n -i hN-eth0

replacing N with the host’s number.

Submission Instructions

You must submit a single tar file of the src directory containing the Java source files for your SDN applications.  Please submit the entire src directory; do not submit any other files or directories. To create the tar file, run the following command, replacing username1 and username2 with the WISC username (NetID) of each group member:

tar czvf username1_username2.tgz src

Upload the tar file to  Canvas. Please submit only one tar file per group.