OpenFlow protocol was proposed to enable research in campus networks. 
As open Flow specification states, today, there is almost no practical way 
to experiment with new network protocols (e.g., new routing protocols, or 
alternatives to IP) in sufficiently realistic settings (e.g., at scale 
carrying real traffic) to gain the confidence needed for their widespread
deployment. Hence most new ideas from the networking research community
go untried and untested. The solution is to have networks designed in
such a way that it follows the two major design principles: modularity
and abstraction. Hence to support this, open Flow protocol is used which
helps in following ways as given in Section 1.

The openFlow protocol is basically a protocol which is used for
communication between an SDN controller and a switch. This protocol lets
the switch talk to the controller about processing of a packet and also
lets the controller alter the switch's flow table. The OpenFlow protocol
is layered on top of TCP, and prescribes the use of TLS. Controllers
should listen on TCP port 6653 for switches that want to set up a
connection.

Open flow switches are categorised into:
1. Dedicated Openflow switches : These forward packets between ports, as 
defined by a controller. 

2. OpenFlow enabled switches : As mentioned earlier, open Flow protocol 
achieves separation of production traffic from experimental traffic.