How do I monitor network traffic of a controller?

To monitor network traffic of a controller, you will require a switch that has support for port mirroring.  Without port mirroring, you can only see the traffic that a controller broadcasts to the network, which will often not be enough data to troubleshoot networking issues.

One low cost switch with port mirroring is the Netgear GS305E.  

To set up, plug the controller to monitor into and a connection to your regular router into Ports 1-4.  Plug your monitoring device (a laptop) into port 5.

Using the NETGEAR Switch Discovery Tool to locate your switch 

https://www.netgear.com/support/product/netgear-switch-discovery-tool.aspx

Click ADMIN PAGE, navigate to System->Monitoring->Mirroring.  Tick the boxes for ports 1-4, select Mirroring Enabled and Destination Port 5 (where your monitor device is connected).

At this point, you can now simply select your regular ethernet interface in wireshark and begin logging.