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
  

  1. Create a new match object.
  2. Add the source MAC address to match on, and turn the wildcard bit for source MAC field (OFPFW_DL_SRC)
  3. set the FlowMod match to the one you just created.

• compiling oflops (cbench Controller Benchmarker). This requires an additional package, libconfig8-dev, in addition to the dependencies listed, so the list becomes:

  autoconf automake libtool libsnmp-dev libpcap-dev libconfig8-dev
  

• creating arbitrary protocol data in Floodlight Ethernet class. You need to
  1. Have a zero-argument constructor, and
  2. add your class and Ethertype to the etherTypeClassMap HashMap

the former is needed for the payload to be de-serialized properly, as class Ethernet calls getInstance() on the class being used as payload. The latter, or else it won't be parsed and casted properly. In addition point 2. implies that your class needs to implement IPacket. The best way to do this is by extending the provided abstract BasePacket class.