Technical Field
The present invention relates generally to information processing and, in particular, to improving the management of unreachable OpenFlow (OF) rules. 
Description of the Related Art
OpenFlow is a communications protocol that gives access to the forwarding plane of a network switch or router over a network.  Physical switches supporting OpenFlow typically have limited ternary content addressable memories.  For example, one particular switch that supports OpenFlow supports 750 OF rules. 
Small TCAMs mean that the software defined network (SDN) controller needs to manage the space accordingly to reduce the rate of packet_in and rule re-installation.  This adds complexity to the SDN controller since the SDN controller needs to add new rules and also determine what current rules will become unreachable and remove them. 
In an SDN environment with a variety of services (even within the same controller), often different services (waypoint, L3, replication) may install rules of different priority that mask rules of lesser priority which then essentially become unreachable rules.  These unreachable rules take up space in the ternary content addressable memory (TCAM) unless they are removed.  The existence of unreachable rules in the TCAM makes debugging and diagnostics more complex since this means more rules must be examined.