Efficient FIB caching using minimal non-overlapping prefixes

The size of the global Routing Information Base (RIB) has been increasing at an alarming rate. As a direct effect, the size of the global Forwarding Information Base (FIB) has experienced rapid growth. This increase raises serious concerns for Internet Service Providers (ISPs) as the FIB memory in line cards is much more expensive than regular memory modules, so frequently increasing this memory capacity for all the routers is prohibitively costly to an ISP. Previous research on Internet traffic indicates that a very small number of popular prefixes receive most of the Internet's traffic, making "caching" a possible solution to reduce the FIB size. However, FIB caching may cause a cache-hiding problem where a packet's longest-prefix match in the cache differs from that in the full FIB, and thus the packet will be forwarded to the wrong next hop. Motivated by these observations, we propose an efficient FIB caching scheme that stores only non-overlapping FIB entries into the fast memory (i.e., a FIB cache), while storing the complete FIB in slow memory. Our caching scheme achieves a considerably higher hit ratio than previous approaches while preventing the cache-hiding problem. It can also handle cache misses, cache replacement, and routing updates efficiently. Moreover, we have implemented the proposed caching scheme using the OpenFlow platform, which allows a local or remote route controller to manage routes in the cache. We use real traffic of a regional ISP and a Tier1 ISP to carry out our experiments. Our simulation results show that with only 20K prefixes in the cache (5.28% of the actual FIB size), the hit ratio of our scheme is higher than 99.95%. Our OpenFlow implementation achieves a hit ratio near 99.94%, which approaches the performance of the simulated results.