Mininet and Opendaylight controller port status update messages

Question

I have a question regarding the communication between Mininet and the Opendaylight controller.

I have a virtual testbed with Mininet and Opendaylight controller. And when I tear down some links between the switches, it is immediately reflected in the ODL web interface.

So I want to know how the Controller gets to know that the network topology has changed. Is it because of the hello messages exchanged between ODL controller and mininet switches? If so, Can anyone tell at what rate the “hello” messages are exchanged between the controller and mininet nodes?

Answer 1

As specified in the OpenFlow specification (which Mininet is in compliance with, v1.1 I think), this is an asynchronous message from switch to controller. Meaning that the controller doesn't ask for updates directly

Port-status: The switch is expected to send port-status messages to the controller as port configuration state changes. These events include change in port status (for example, if it was brought down directly by a user) or a change in port status as specified by 802.1D (Spanning Tree Protocol)

The switch can also ask for this information in a symmetrical way, through Read-state messages.

Start Wireshark and look at the packets sent between controller and switch yourself. This will give you the best understanding of what is going on.

Answer 2

continuation with the question.|

As per my knowledge port status is updated in operational datastore and then a notification is triggered for the registered listeners. generally some flows-add/mod follows but my question is where/what is the mapping of data update in oper DS and flows being pushed to switch.

To answer your question, hello message will be one time message that switch will send to connect to controller then controller will be issuing echo message/request and switch will echo reply. You can capture wireshark between controller and switch to better understand this.