Update Cost-Aware Cache Replacement for Wildcard Rules in Software-Defined Networking

In Software-Defined Networking (SDN), Ternary Content Addressable Memory (TCAM) enables fast lookup with flexible wildcard rule patterns for flow tables, however, the scarcity and expensiveness of TCAM dramatically limit the number of rules that switches can support. Rule caching for TCAM breaks the flow table size constraint by appropriate combinations of hardware and software processing. Nevertheless, previous literatures, from the viewpoint of maximizing cache hit ratio, ignore the TCAM update operations incurred by cache replacement, which is severely time-consuming. In this paper, we solve the TCAM cache replacement problem from a standpoint of reducing update cost. Upon comprehensively analyze and measure on cache hit ratio and update cost while sticking to the rule dependency constraints, we propose an effective cache replacement algorithm that can dynamically and adaptively adjust TCAM rules on a switch. Our experimental results show that our proposed algorithm can effectively eliminate over 60% update operations with less than 5% cache hit loss.