On the Aggregatability of Router Forwarding Tables

The rapid growth of global routing tables has raised concerns among many Internet Service Providers. The most immediate concern regarding routing scalability is the size of the Forwarding Information Base (FIB), which seems to be growing at a faster pace than router hardware can support. This paper focuses on one potential solution to this problem - FIB aggregation, i.e., aggregating FIB entries without affecting the forwarding paths taken by data traffic. Compared with alternative solutions to the routing scalability problem, FIB aggregation is particularly appealing because it is a purely local software optimization limited within a router, requiring no changes to routing protocols or router hardware. To understand the feasibility of using FIB aggregation to extend router lifetime, we present several FIB aggregation algorithms and evaluate their performance using routing tables and updates from tens of networks. We find that FIB aggregation can reduce the FIB table size by as much as 70% with small computational overhead. We also show that the computational overhead can be controlled through various mechanisms.