OpenFlow Miscellany

This page documents various odds-and-ends regarding OpenFlow and related platforms, tools, and whatnot.

• Using xterm with mininet hosts. You can background then by doing:

  mininet> h1 xterm &
  

  this allows you to spawn a terminal for a switch, from which you can, say, sniff packets using wireshark.

• A good way to track packets and transactions between datapath and controller is via buffer Id for switch-initiated conversations, and by XID for controller-initiated transactions. A caveat is that the buffer ID is only applicable to a subset of messages e.g. PacketIns and PacketOuts. A -1 buffer ID indicates a controller-generated packet (e.g. by a flow pushing tool or via a REST API for static flows).

• making FlowMods. If not building a match object from a PacketIn, make sure to not forget to invert the wildcard bit for the field you are setting. The default match is wildcarded to all. For example, to make a match object that only inspects source MAC address of an Ethernet header:

   (1)    OFMatch m1 = new OFMatch();
   (2)    m1.setDataLayerSource(hwaddr);
  	   m1.setWildcards(OFMatch.OFPFW_ALL & ~OFMatch.OFPFW_DL_SRC);
  
   (3)    flowmod.setmatch(m1);   //and other params as necessary