wiki:GIMI-GEC16-Tutorials/GIMI-GEC16-TutorialA

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Combined ExoGENI/GIMI Tutorial at GEC 16

Victor J. Orlikowski, Duke - vjo@duke.edu
Mike Zink, U. Mass. Amherst - zink@ecs.umass.edu

Tutorial is based on initial research and materials provided by Rajesh Gopidi (rajesh@renci.org)

For GIMI related questions send email to: geni-gimi-users@googlegroups.com

Description

In this tutorial experimenters will perform SDN/OpenFlow (OF) experiments based on provisioned Layer 2 topologies in ExoGENI and VMs running OVS (which implements OF 1.0, 1.2 and 1.3) that mimic the behavior of hardware-based OF switches. The goal is to learn how to provision a topology, how to attach a controller to it, demonstrate basic packet manipulation capabilities using most likely gui-based tools that use north-bound APIs on floodlight (as an exemplar controller). As an additional goal, experimenters will learn how to obtain statistics from measurements on this slice and how these statistics can be used to change flows with the aid of GIMI tools.

Back to GEC16 GIMI tutorials main page

Openflow Tutorial

1.0 Getting Started

To get started ensure that you have flukes up and running on your system. If do not know how to install flukes please take a look at this page: Flukes.

For this tutorial you will need an image with OVS pre-installed in it. Don't panic, RENCI provides you an image that has OVS installed in it. To use that, all you need to do is, open the “.flukes.properties” file in your home directory and add the following lines at the bottom of it.

image2.name=gimi-ovs
image2.url=http://emmy9.casa.umass.edu/Disk_Images/ExoGENI/exogeni-umass-ovs-1.0.2.xml
image2.hash=de35e71b31771870bcdfcccb4dee11657ba145b8

Now, to check if flukes is able to read the image option, open flukes and create a node by left clicking in the request view pane. After creating the node, right click and select edit properties. You should be able to find an option in the images section with the name “gimi-ovs”.


Figure (1)

With that you have successfully completed the first step. In the next step, you need to run an Openflow controller and ensure that it is reachable via Internet. You can run any Openflow controller that is available, but we will be using floodlight controller for this tutorial.

If you don't have access to a system with a public IP, you can create a sliver on your slice with a separate node to run floodlight controller. You can get the public IP of a node in Flukes by going to 'Resource View' , right clicking on the node and checking under 'Properties'.

We have also created a video that demonstrate how to create the ExoGENI slice we are using in this tutorial!

2.0 Running an Openflow Controller

You can download floodlight by clicking on this link Floodlight.
Download the jar file as well as the floodlightdefault.properties file.

In the properties file, delete the line “net.floodlightcontroller.forwarding.Forwarding,\“ and save the file. Now, open a new terminal on the box where you are planning to run the controller and type the following line.

“java -jar <floodlight jar file name including “.jar”> -cf <path to the modified properties file>"

If you find the output on your console similar to the ones in the screen shot below then you are done with setting up the controller.


Figure(2)

Final missing piece is “Avior”, a GUI based tool which is used to manipulate flow entries in the switches via user friendly interface rather than rest API. Click on the link below to download the jar file and start running the tool.

OpenFlow : Getting Started
For the tutorial VM, you will need the 32-bit Linux Avior.

For smooth operation, run this tool on the same box where the controller is running. When you type “java -jar <path to the Avior jar file>” you should be getting a prompt similar to the one show below.

Enter <public IP of node> as the IP and click on launch button.


Figure(3)

NOTE: Ensure that the controller is running and is reachable from this box.

After clicking on the launch button, a new GUI appears on the screen similar to the one shown below.

Figure(4)

Now you are all set for your first Openflow experiment on ExoGeni.

3.0 Running a simple experiment

3.1 Life of an ICMP packet in an Openflow network:

3.1.0 Creating a topology

First, we are going to create a simple six node topology with four nodes acting as switches and rest of them as hosts.


Figure (5)

Here, nodes 0 and 5 are the hosts and rest of them are switches.

Now we need to configure each node before we submit the request for resource allocation. This can be done by editing the properties of each node [right click and select edit properties].

Configure each switch [nodes 1,2,3,4] using the screen shots below as a reference. Configure IP addresses on each node in such a way that you can tell which node is on the other side of the link by looking at the IP. For example: link 3 connects nodes 2 and 0, hence IP address on node 2 is configured as 192.168.1.20 to indicate that node 0 is on the other end of the link. Also, select ovs_image as the image to be used.
Lastly, in the post boot script, copy and paste the commands shown below:

#!/bin/bash
ovs-vsctl add-br test
ovs-vsctl add-port test eth1
ovs-vsctl add-port test eth2
ovs-vsctl add-port test eth3
ovs-vsctl set-controller test tcp:<controller ip address>:6633
ovs-vsctl set-fail-mode test secure

Note:This step has already been performed for the requests you will be using in the tutorial.

The above commands are used to create a data path or a switch [named as test] and add interfaces to it.

The last command configures the controller's IP and port number details using the set-controller command.

Note: Do not forget to add the controller's IP address in the set-controller command.


Figure (6)

The above steps have to be repeated on the remaining three switches.

After we finish configuring switches, we need to configure the hosts. Except for the step where we add the OVS commands to the post boot script all the other steps described above are to be followed. To distinguish the hosts from switches, configure the interfaces with IP address from a different sub-net, say 192.168.2.0/24.
Once you are done configuring the nodes, go ahead and submit the slice by giving it a name. You can check the status of your request in the manifest view by specifying the name of the slice in the text box and clicking on the “Query for manifest” button.

When you notice status of all the nodes as active, switch to the controller's terminal and you should be able to see logs similar to the ones in the below screen shot.


Figure(7)

3.1.1 Mapping Nodes to their DPIDs

Now, switch over to the Avior’s control panel. You should be able to see four switches listed along with their DPIDs'.


Figure(8)

Since we cannot modify DPIDs to a more readable format, we need to manually map the nodes to their DPIDs. To do that, we need to login into each switch/node and type the below command.

“ovs-ofctl show test”


Figure(9)

As you can see in the above screen shot, DPID is displayed in the first line of the output. Carefully map each node/switch to its DPID so that you can follow the rest of tutorial with out any issues. Below is the mapping used while writing this tutorial.


Figure(10)

The following figure shows an example configuration of the ExoGENI slice.
Note: The IP addresses and the interface names will always be as shown in Figure 11 but the OpenFlow (OF) ports are assigned dynamically and can be different in the case of your specific slice! This video explains how the OF port numbers can be determined.


Figure(11)

3.1.2 Configure static ARP entries on the hosts

To make our life easier we are going to configure static ARP entries on both the hosts. If you plan to move forward without configuring static ARP entries then you need to install flow rules specific to ARP packets, which will double the work. [FYI: we have disabled learning switch on the controller as well as in OVS]. You can configure static ARP entries using the command “arp -s <ip> <mac>”. For example: "arp -s 192.168.2.6 fe:16:3e:00:57:b3 -i eth1” is used to specify that host with IP address “192.168.2.6” and MAC address “fe:16:3e:00:57:b3” can be reached via interface eth1.

Similarly, configure the static ARP entry on the other host (node 5).

3.1.3 Configure flows

In this experiment, we are going to route the ICMP request packets from the node0 via “node1 → node3 → node5” path and ICMP replies from node5 along the path “node3 → node4 → node2 → node1 → node0”. To do that, we need to know the Openflow port numbers of interfaces on each switch.

One way to find out is to use the command “ovs-ofctl show test” on each switch (refer to figure[9]) and make a note of them.

To configure a flow, switch to Avior's control panel [do not panic if it gets struck while you are in middle of something. Restart it and start over from the beginning] and click on the drop down arrow beside tools. You will be able to find “flow manager” option. Switch to the flow manager window and select the switch [using the mapping created] to inset a flow entry and then click on new flow.


Figure(12)

As you can see in the screen shot below, you will be asked to configure four fields. First, enter a name for the flow, say “ICMP request flow_<dest ip>”. Next, click on actions and select output from the drop down box and enter the port number [look into mapping between the interfaces and ports] you want the packet to exit the switch from and click on save.


Figure (13)


Figure (14)

Now, click on match option and enter appropriate values for different fields as show in Figure [13].
Ensure that you enter the right input port value and also data layer type.

Lastly, save the match information and click on push. You should get a status message indicating that your flow was pushed successfully.


Figure(15)

Carefully follow the same procedure and insert flows accordingly in all the switches. The procedure is same for both ICMP requests as well as ICMP replies. All you need to do is type in the right input port and output port values and the destination IP.

After you have configured all the four switches, nodes 1 & 3 should end up with two flow entries and the other two switches [2 & 4] with one entry each. Verify your flow entries with the entries shown in the below screen shots.


Figure(16): node1 flow entries


Figure(17): node3 flow entries


Figure(18): node4 flow entries


Figure(19): node2 flow entries

3.1.4 Run experiment - The PING test

After verifying all the flow entries, start sending ping packets from node0 to node5. Ensure that ping packets originate from the right interface i.e. the source IP should be 192.168.2.2. One way to do that is using the -I option of ping command. For example: if interface eth1 is configured with IP “192.168.2.2” then we need to use the command “ping 192.168.2.6 -I eth1” for the ping to pass.

In case you don't see any ping replies then you can debug the packet path using packet counters, which indicate whether packets were hitting the TCAM entry [see the “packets column of the flow entry in the above screen shot”]. If the counter doesn't increment then cross check the flow entry on that switch as well as the flow entries on other switches to ensure that packets are being forwarded on the right path. You can also use “tcpdump” tool to monitor packets on an interface. Moreover, OVS provides a way to monitor packets being forwarded by a switch using “ovs-vsctl snoop <bridge name>” command. [replace bridge name with test for this experiment].

Now, that we have successfully completed the ping test. Lets try to break it. There are many ways to do it. One can delete one of the flow entries or remove the static ARP entries on one of the hosts. Lets do the later one by removing the ARP entry on node5 using the command “arp -d 192.168.2.2”. Now, the packet counters increase along the flow path “node1 → node3 → node5” and remain constant along the flow path “node5 → node3 → node4 → node2 → node1 → node0”.



Figure(20): Flow entries on node 1

I hope you found the tutorial useful. Keep experimenting with different topologies and configurations.

LabWiki

After the ExoGENI slice has been created and the flows in the topology are appropriately configured we will now use the GIMI tools to perform a measurement on top of this slice.

To Perform this measurement we will make use of LabWiki.

A tutorial on how to use LabWiki. for measurements can be found here. In addition, we have created a video that demonstrates the usage of LabWiki.

The slides that were presented during the GIMI part of the tutorial can be found here.

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