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+                      v19
 . To see messages go between your switch and your controller, open a new ssh window to your controller node and run tcpdump on the `eth1` interface and on the tcp port that your controller is listening on usually 6653.  (You can also run `tcpdump` on the `OVS` control interface if you desire.)
 {{{
 sudo tcpdump -i eth1 tcp port 6653
+sudo tcpdump -i eth0 tcp port 6653
 }}}
   You will see (1) periodic keepalive messages being exchanged by the switch and the controller, (2) messages from the switch to the controller (e.g. when there is a table miss) and an ICMP Echo message in, and (3) messages from the controller to the switch (e.g. to install new flow entries).
 …
 When the wireshark window pops up, you might still have to choose eth0 for a live capture.  And you will want to use a filter to cut down on the chatter in the wireshark window.   One such filter might be just seeing what shows up on port 6633. To do that type ''tcp.port eq 6633'' in the filter window, assuming that 6633 is the port that the controller is
 listening on.   And once you have lines, you can choose one of the lines and choose "Decode as ...." and choose the ''OFP protocol''.
+[[Image(GENIExperimenter/Tutorials/Graphics:4NotesIcon_512x512.png, 5%, nolink)]]
+Make sure that you have a suitable '''X.org''' software component such as [https://www.xquartz.org/ XQuartz] on your local machine for Wireshark to work.
 === 4e. Web GUI ===