Wildcard Compression of Inter-Domain Routing Tables for OpenFlow-Based Software-Defined Networking

In this paper we consider carrier networks using only OpenFlow switches instead of IP routers. Accommodating the full forwarding information base (FIB) of IP routers in the switches is difficult because the BGP routing tables in the default-free zone currently contain about 500,000 entries and switches have only little capacity in their fast and expensive TCAM memory. The objective of this paper is the compression of the FIB in acceptable time to minimize the TCAM requirements of switches. The benchmark is simple prefix aggregation as it is common in IP networks where longest-prefix matching is applied. In contrast, OpenFlow-based switches can match general wildcard expressions with priorities. Starting from a minimum-size prefix-based FIB, we further compress that FIB by allowing general wildcard expressions utilizing the Espresso heuristic that is commonly used for logic minimization. As the computation time of Espresso is challenging for large inputs, we provide means to trade computation time against compression efficiency. Our results show that today´s FIB sizes can be reduced by 17% saving up to 40,000 entries and the compression time can be limited to 1 - 2s sacrificing only 1% -- 2% compression ratio.