OpenFlow Table Basics

OpenFlow Flow Table has following three things:

Header Field, Action, Counters

Header Field:
     Each flow table header entry is made up of six components, which define the matching rules and
     other basic rules for the corresponding flow.

     Match Fields:  Used to select packets that match the values in the fields
             Ingress Port, Ethernet Source, Ethernet Destionation, Ethernet Type, VLAN ID,
             VLAN Priority, IP Source, IP Destination, IP Protocol, IP ToS Bits,
             TCP/UDP Source Ports, TCP/UDP Designation Ports


     Priority: Relative priority of table entries.
     Counters: Updated for matching packets
     Instructions:  Actions to be taken if a match occurs
     Timeouts: Maximum amount of idle time before a flow is expired by the switch
     Cookie: Opague data value chosen by the controller


Action:
     Each flow entry is associated with zero or more actions that dictate how the device handles
     matching packets. Actions in OpenFlow specification are defined as required and optional.
     Optional actions are not required to be implemented by vendors as such.

     Forward:   required actions are ALL, Controller, Local, Table, In-Port
                       optional actions are Normal, Flood
     Drop: required
     Modify Field: optional


Counters:
     Counters are maintained per-table, per-flow, per-port and per queue. There are a set of required
     counters that all the implementations should support and there are additionally optional counters.
     Here are various counters:

     Table: Active entries, Packet Lookup, Packet Matches

     Flow: Received Packets, Received Bytes, Duration (seconds), Duration(nanoseconds)

     Port: Received Packets, Transimitted Packets, Received Bytes, Transimitted Bytes,
              Receive Drops, Transmit Drops, Receive Errors, Receive Frame Alignment Errors,
              Receive Overrun Errors, Receive CRC Errors, Collisions

     Queue: Transmit Packets, Transmit Bytes, Transmit Overrun Errors
   
Examples:

     match=(eth.src[40]), action=(drop;)

a broadcast/multicast source MAC, gets dropped

     match=(vlan.present), action=(drop;)

Anything with a logical VLAN tag.