Abstract-Snapshots of the Forwarding Information Base (FIB) in Internet routers can be compressed (or aggregated) to at least half of their original size, as shown by previous studies. However, the permanent stream of updates to the FIB due to routing updates complicates FIB aggregation in practice: keeping a (near-)optimally aggregated FIB in face of these routing updates is algorithmically challenging. A sensible trade-off has to be found between the aggregation gain and the complexity of handling routing updates. This paper investigates whether the spatial and temporal locality properties of routing updates conceal opportunities for improving this trade-off in online FIB aggregation.Our contributions include an empirical study of the locality of updates in public Internet routing data. To facilitate this study, we design the Locality-aware FIB Aggregation (LFA) algorithm. We show, that an algorithm as simple as LFA can effectively leverage the locality of FIB churn to keep low the number of updates to the aggregated FIB, as within time periods of a few seconds or minutes, routing updates affect only a limited number of regions in the FIB.
I. INTRODUCTIONAt a high level, Internet routers are built around a route processor which runs routing protocols and makes routing decisions, and a forwarding plane which forwards packets according to the decisions of the route processor. The crucial link between the two components is the Forwarding Information Base (FIB), containing the forwarding rules. The route processor inserts and deletes FIB entries according to its route computations. The forwarding plane uses the FIB to perform an IP destination lookup on each incoming packet. This requires the FIB to support very fast IP destination lookups so that packets can be forwarded at line-rate. In addition, the FIB needs to support frequent updates to the forwarding rules due to the churn in the BGP routing table. Finally, the number of forwarding rules that a FIB needs to keep is growing over time, putting extra pressure on the FIB memory capacity. 1 To fulfill all these requirements, FIB memory used in today's enterprise-grade to high-end routers is a highly specialized component, expensive, and power-hungry. It is also considered a main limiting factor in terms of a router's lifetime [12].A natural and local solution to mitigate the problembefore possible long-term solutions are deployed -is the aggregation (or compression) of the FIB, i.e., the replacement of the existing set of rules by an equivalent but smaller set. The aggregation of FIB rules has the appealing property that it is a purely local solution, in the sense that it does not affect neighboring routers and it can be realized by the route processor through only software modifications.