Infinite CacheFlow in software-defined networks

Software-Defined Networking (SDN) enables fine-grained policies for firewalls, load balancers, routers, traffic monitoring, and other functionality. While Ternary Content Addressable Memory (TCAM) enables OpenFlow switches to process packets at high speed based on multiple header fields, today's commodity switches support just thousands to tens of thousands of rules. To realize the potential of SDN on this hardware, we need efficient ways to support the abstraction of a switch with arbitrarily large rule tables. To do so, we define a hardware-software hybrid switch design that relies on rule caching to provide large rule tables at low cost. Unlike traditional caching solutions, we neither cache individual rules (to respect rule dependencies) nor compress rules (to preserve the per-rule traffic counts). Instead we ''splice'' long dependency chains to cache smaller groups of rules while preserving the semantics of the network policy. Our design satisfies four core criteria: (1) elasticity (combining the best of hardware and software switches), (2) transparency (faithfully supporting native OpenFlow semantics, including traffic counters), (3) fine-grained rule caching (placing popular rules in the TCAM, despite dependencies on less-popular rules), and (4) adaptability (to enable incremental changes to the rule caching as the policy changes).