= 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
   }}}