This tutorial is an introduction to how SDN-IP runs in practice. We'll go through starting up a simple emulated network, and we'll see how SDN-IP controls this network to move data from place to place.
If you haven't done so already, it's highly recommended that you go through the ONOS Tutorial first. This will give you some familiarity with the basic functionality of ONOS. In addition, you should read through the SDN-IP Architecture <LINK> document to get an overview of how SDN-IP works.
Hopefully you've already done the ONOS tutorial, so you already have the ONOS tutorial VM available. If not, check out the Setup your environment <LINK> section of the ONOS tutorial to get the VM ready.
The network topology
We've prepared a simple emulated Mininet topology, which contains 6 OpenFlow switches. Connected around the edges of the SDN network are 4 emulated routers. The routers run Quagga, which is an open-source routing suite. In our case we run the BGP part of Quagga on them, to simulate external BGP routers belonging to other administrative domains. The goal of SDN-IP is to be able to talk BGP with these routers in order to exchange traffic between the different external ASes.
This figure shows the topology as observed by ONOS. We can see 6 blue OpenFlow switches, and 5 hosts around the edge.
- The host labelled "bgp" is our Internal BGP Speaker. It sits inside our SDN network, and its job is to peer with all the External BGP Routers, learn BGP routes from them, and relay those routes to the SDN-IP application running on ONOS.
- The other four hosts, labelled r1 through r4, are the External BGP Routers. They are the border routers that reside in other networks that want to exchange traffic with us.
- Behind each router is a host, and these are labelled h1 through h4 in Mininet. ONOS can't see these hosts, because they reside in other networks that are not controlled by ONOS.
Start up the network
Double-click the "SDN-IP Mininet" icon on the desktop to start up the network.
We can look at the configuration of the hosts in the Mininet terminal.
Each host is in a different IP subnet. When SDN-IP is up and running, these hosts will be able to communicate with one another despite being in different networks. This is because the SDN network is able to route traffic based on BGP routes.
Also, double-click the "ONOS" icon on the desktop to start up the ONOS console. If you run the "devices" command, you should see the network has started up and connected to ONOS.
Running SDN-IP for the first time
If you try and ping between any two hosts right now, you'll notice nothing is working.
Even though ONOS is running and connected to switches, there are no applications loaded so there is nothing to tell ONOS how to control the network. We can also use the summary command to verify there are no flows or intents in the network.
Install the application
First we need to install some helper applications that SDN-IP relies on. These features let ONOS read in various configuration files and respond to ARP requests on behalf of hosts.
Now lets install the SDN-IP application so we can get some traffic flowing between our networks.
A lot happens as soon as we install the SDN-IP application. The first thing it does is install point-to-point intents to allow the external BGP peers to communicate with our internal BGP speaker. This allows the external BGP routers to relay the routes they are capable of forwarding through to SDN-IP.
We can see the routes that SDN-IP has learnt with the "routes" command.
Don't worry if you don't see all of the routes straight away - sometimes it takes a minute or so for the BGP sessions to establish and advertise the routes to ONOS.
Now that ONOS has learnt some routes, it has programmed those routes into the switches using the intent API. If we look at the intent summary, we can see the different intents that SDN-IP is using.
We see a total of 28 intents. The 24 PointToPointIntents are simple end-to-end flows which allow the external BGP routers to communicate with our internal BGP speaker. The three MultiPointToSinglePoint intents are the forwarding rules for the routes that we've learnt through BGP. Each route is translated into one MultiPointToSinglePoint intent which matches the traffic for that route at the ingress ports of the network, and forwards it along to the router who advertised the route to us. This is how we use routing information learnt from BGP to enable traffic to transit our network on these routes.
Now that the intents are installed, we can ping through the network. Go back to the Mininet console and try ping between a pair of hosts.
The ping succeeds! You can try pinging between some of the other hosts such as h1, h2 and h3. We can't ping h4 yet, but we'll address that in the next section.
Advertising a new route
Now that we've got a the system up and running, let's see what happens when there's a change in the BGP routes. We're going to make one of the external routers advertise a new route, which will allow us to talk to a new host. Right now r4 is not advertising any routes, and so we can't talk to h4. Let's verify this by trying to ping h4.
Yep, looks like we can't reach h4 yet.
To make r4 advertise a new route, we have to change the configuration of the BGP router. In our case, the BGP router is a Quagga process, so we'll connect to the Quagga CLI and configure r4 to advertise a new route. (The Quagga CLI is complex and includes lots of options, but considering this is not a Quagga tutorial we don't have the time to explain too much about Quagga. If you're interested, there's material online that will help you understand Quagga).
First, from the Mininet CLI we can start up an xterm so we can connect to the Quagga CLI.
A little xterm window will pop up. The next few commands will by typed into this xterm window.
We can use telnet to connect to the Quagga BGP CLI.
It will prompt for a password, which is sdnip. Once the password is entered, we'll drop into a prompt
Now we can begin to configure the router to advertise a new network.
Now our external router r4 has advertised a new route to our SDN network. We're done with the xterm window, so you can close it. Let's go back to our ONOS terminal and see if ONOS has received the new route.
We see the new route to 192.168.4.0/24 has appeared in the list. Also, when SDN-IP received the route it installed a new MultiPointToSinglePoint intent into the network.
Our number of MultiPointToSinglePoint intents has increased to 4. Now let's see if we can ping to our new network.
Great! Now we can ping to h4 which is in the network we just received through BGP. This shows that whenever the routes learnt through BGP are updated, SDN-IP reacts to the update and programs the dataplane accordingly.
Thanks for completing the SDN-IP tutorial. Now that you've had a glimpse of how SDN-IP works, feel free to poke around and explore the system further. If you're looking to run SDN-IP in your own network, head over to the Users Guild <LINK> to learn more about configuring and deploying the application.
In addition, the scripts used to create the network are in the ONOS repository. The Mininet topology is in
tools/test/topos/sdnip/tutorial.py. The router configurations are in
tools/test/topos/sdnip/configs/. Feel free to take a look and see how the network is put together if you're interested.