Adding flows in OpenDaylight using Python and REST API

Building on my last post I’ve put together a small script that will find the shortest path between two switches, then install some flows to create a path between them. I’m leveraging some tools from the NetworkX library in Python and the Northbound REST API on the OpenDaylight controller.

I’m using Mininet as my test network, and the built-in tree topology that was used previously. When loaded into the controller the topology looks like this:

Mininet creates two hosts off each leaf node. The end goal here is to ping between H1 and H8, which are connected to S3 (port 1) and S7 (port 2). First I want to get the shortest path between S3 and S7. To do that I load the nodes(switches) and edges(links) into a NetworkX Graph object:

I wrote a helper function to make building the URLs for the REST calls a little easier. The URL path to get the edges is:/controller/nb/v2/topology/default/

This returns a list of ‘edgeProperties’. An edge has a headNodeConnector and a tailNodeConnector, which are the ports on either end of the edge (each edge is unidirectional, so there will be two entries for each link). These NodeConnectors have nodes associated with them that I use to create tuple to signify an edge. For example, the edge between S4 and S2 has a headNodeConnector of:

            "edge": {
                "tailNodeConnector": {
                    "@type": "OF",
                    "@id": "2",
                    "node": {
                        "@type": "OF",
                        "@id": "00:00:00:00:00:00:00:02"
                    }
                },
                "headNodeConnector": {
                    "@type": "OF",
                    "@id": "3",
                    "node": {
                        "@type": "OF",
                        "@id": "00:00:00:00:00:00:00:04"
                    }
                }

From which I extract the node id’s (i.e. OpenFlow IDs) to create a tuple:
(00:00:00:00:00:00:00:04, 00:00:00:00:00:00:00:02)
And then add that as an edge to my Graph object. You’ll also see the ID of the NodeConnector itself as one of the attributes, which we’ll use later when defining ingress and output ports for our flows. Here’s code:

# Get all the edges/links
resp, content = h.request(build_url(baseUrl, 'topology', containerName), "GET")
edgeProperties = json.loads(content)
odlEdges = edgeProperties['edgeProperties']

# Put nodes and edges into a graph
graph = nx.Graph()
for edge in odlEdges:
  e = (edge['edge']['headNodeConnector']['node']['@id'], edge['edge']['tailNodeConnector']['node']['@id'])
  graph.add_edge(*e)

I do something similar with the nodes, using the URL path: /controller/nb/v2/switch/default/nodes
That returns a list of all the switches in the network, and I add them as nodes to the graph.

# Get all the nodes/switches
resp, content = h.request(build_url(baseUrl, 'switch', containerName) + '/nodes/', "GET")
nodeProperties = json.loads(content)
odlNodes = nodeProperties['nodeProperties']
for node in odlNodes:
  graph.add_node(node['node']['@id'])

Now I run Djikstra’s algorithm provided by the shortest_path method. This returns a list of nodes along the shortest path.

shortest_path = nx.shortest_path(graph, "00:00:00:00:00:00:00:03", "00:00:00:00:00:00:00:07")

In this case the list is:
[00:00:00:00:00:00:00:03, 00:00:00:00:00:00:00:02, 00:00:00:00:00:00:00:01, 00:00:00:00:00:00:00:05, 00:00:00:00:00:00:00:07]

Now I can build a series of flow entries for each switch along the path, not counting the ones directly connected to the hosts. To do this I created a couple functions. find_edge will look for an edge that has a particular head node and tail node. push_path takes a path and the edges from the API call and pushes the appropriate flows to the switches. To create a flow on the switch I use an HTTP POST and send over a JSON object that describes the flow. An example JSON flow entry object:

{"installInHw":"false","name":"test2","node":{"@id":"00:00:00:00:00:00:00:07","@type":"OF"}, "ingressPort":"1","priority":"500","etherType":"0x800","nwSrc":"10.0.0.7","nwDst":"10.0.0.3", "actions":"OUTPUT=2"}

And the code:

def find_edge(edges, headNode, tailNode):
  for edge in odlEdges:
    if edge['edge']['headNodeConnector']['node']['@id'] == headNode and edge['edge']['tailNodeConnector']['node']['@id'] == tailNode:
      return edge
  return None

def push_path(path, odlEdges, srcIP, dstIP, baseUrl):
  for i, node in enumerate(path[1:-1]):
    flowName = "fromIP" + srcIP[-1:] + "Po" + str(i)
    ingressEdge = find_edge(odlEdges, shortest_path[i], node)
    egressEdge = find_edge(odlEdges, node, shortest_path[i+2])
    newFlow = build_flow_entry(flowName, ingressEdge, egressEdge, node, srcIP, dstIP)
    switchType = newFlow['node']['@type']
    postUrl = build_flow_url(baseUrl, 'default', switchType, node, flowName)
    # post the flow to the controller
    resp, content = post_dict(h, postUrl, newFlow)

def build_flow_entry(flowName, ingressEdge, egressEdge, node, srcIP, dstIP):
  # Since I don't specify the EtherType, it looks like the IP field is ignored
  # Alternatively I could add a second flow with 0x806 for ARP then 0x800 for IP
  defaultPriority = "500"
  newFlow = {"installInHw":"false"}
  ingressPort = ingressEdge['edge']['tailNodeConnector']['@id']
  egressPort = egressEdge['edge']['headNodeConnector']['@id']
  switchType = egressEdge['edge']['headNodeConnector']['node']['@type']
  newFlow.update({"name":flowName})
  newFlow.update({"node":ingressEdge['edge']['tailNodeConnector']['node']})
  newFlow.update({"ingressPort":ingressPort, "priority":defaultPriority})
  newFlow.update({"nwSrc":srcIP, "nwDst":dstIP})  # This can probably be ignored for this example
  newFlow.update({"actions":"OUTPUT=" + egressPort})
  return newFlow

def post_dict(h, url, d):
  resp, content = h.request(
      uri = url,
      method = 'POST',
      headers={'Content-Type' : 'application/json'},
      body=json.dumps(d),
      )
  return resp, content

A few things to note:

• I didn’t specify an EtherType so that it will send any packet over the links. I needed to do this so that ARP messages would make it across. But in doing so, the IP addresses are ignored. This works fine for my simple example, but I think I may revise this later to handle both ARP and IP separately so that there are not such broad flow entries installed. Then I could specify IP match criteria.
• I chose to not install the flow to the switch immediately so that I can take a look at them before actually putting them to work (InstallInHw : false)
• I’m not yet error checking on the response, but you should get an HTTP 201 for successful flow entries.

After pushing these flows, I reverse the path, and push the reverse path onto the switches:

shortest_path.reverse()
push_path(shortest_path, odlEdges, dstIP, srcIP, baseUrl)

Finally I add the entries for the leaf nodes connected to the hosts. There is probably a way to do this with host tracker to make this dynamic, but I just hardcoded it for now:

node3FlowFromHost = {"installInHw":"false","name":"node3from","node":{"@id":"00:00:00:00:00:00:00:03","@type":"OF"},"ingressPort":"1","priority":"500","nwSrc":"10.0.0.1","actions":"OUTPUT=3"}
node7FlowFromHost = {"installInHw":"false","name":"node7from","node":{"@id":"00:00:00:00:00:00:00:07","@type":"OF"},"ingressPort":"2","priority":"500","nwSrc":"10.0.0.8","actions":"OUTPUT=3"}
node3FlowToHost = {"installInHw":"false","name":"node3to","node":{"@id":"00:00:00:00:00:00:00:03","@type":"OF"},"ingressPort":"3","priority":"500","nwDst":"10.0.0.1","actions":"OUTPUT=1"}
node7FlowToHost = {"installInHw":"false","name":"node7to","node":{"@id":"00:00:00:00:00:00:00:07","@type":"OF"},"ingressPort":"3","priority":"500","nwDst":"10.0.0.8","actions":"OUTPUT=2"}
postUrl = build_flow_url(baseUrl, 'default', "OF", "00:00:00:00:00:00:00:03", "node3from")
resp, content = post_dict(h, postUrl, node3FlowFromHost)
postUrl = build_flow_url(baseUrl, 'default', "OF", "00:00:00:00:00:00:00:07", "node7from")
resp, content = post_dict(h, postUrl, node7FlowFromHost)
postUrl = build_flow_url(baseUrl, 'default', "OF", "00:00:00:00:00:00:00:03", "node3to")
resp, content = post_dict(h, postUrl, node3FlowToHost)
postUrl = build_flow_url(baseUrl, 'default', "OF", "00:00:00:00:00:00:00:07", "node7to")
resp, content = post_dict(h, postUrl, node7FlowToHost)

Ok, after all that, I can run my script and then go to the controller to see all the flows added.

Now I install them into the switches by clicking on a flow and then ‘Install Flow’.

After the flows have all been installed, I can then try out my pings in mininet:

And just for good measure I can go over to the Troubleshooting tab on the controller to see the stats of these flows, and see how packets are matching on my flow entries.

You can find the complete script on Github: https://github.com/fredhsu/odl-scripts/tree/master/python/addflow