OpenDaylight: OpenFlow FLOW_MOD messages

Question

I'm studying SDNs and using different controllers (Floodlight 1.1, OpenDaylight Lithium-SR2). I have 2 VMs which can communicate via a private network. In the first VM there is the SDN controller, while in the second VM I can setup a network topology with Mininet via a Python script.

My goal is to find out the controller behaviour: given a topology with 5 switches (with loops) and only 2 hosts, after a "ping" command, which switch does the controller select for the path between hosts?

A "ping" command in Mininet implies ARP traffic (discovering hosts' MAC addresses) and ICMP echo requests/replies. After a ARP_REPLY we see a PACKET_IN from the switch linked to the answering host and the controller sends a FLOW_MOD message to all the switches it selects for the path, according with OpenFlow 1.0 protocol. Look at this Sequence Diagram for an example.

I captured the traffic with "tcpdump" tool and studied it with Wireshark.

Using Floodlight I can see FLOW_MOD messages which include "src" and "dst" MAC addresses (to create the path), but not with OpenDaylight (there are FLOW_MOD messages, but only before ARP traffic and only with broadcast "src" and "dst" MAC addresses).

I would like to understand why I'm not able to see FLOW_MOD messages with correct MAC addresses "src" and "dst" AFTER ARP replies (and not BEFORE). I don't know if it depends on controller's code or on OpenFlow protocol.

Thanks in advance for your help.

Answer 1

I found the problem: ODL works in Proactive mode as default, so I wasn't able to see Flow_Mod messages with attached MAC addresses after ARP traffic. I set ODL in Reactive mode modifying some configuration files which are located in the [ODL-folder]/etc/opendaylight/karaf/ directory of the Controller folder:

• 54-arphandler.xml : by default, the property <is-proactive-flood-mode> is setted to true, so ODL works in Proactive mode. If you want Hybrid mode set that property to false and <is-hybrid-mode> to true. If both properties are setted to false ODL works in Reactive mode.
• 58-l2switchmain.xml : set the property <is-install-dropall-flow> to false. In this way switches send packets that don't have a match (in the switch flow table) to the controller without dropping.

Now I can see Flow_Mod messages with attached MAC addresses and check which switch is choosen by ODL to build the path between hosts.