Merit Network This document analyzes Network Layer Reachability Information (NLRI) flow within a router with emphasis on the Forwarding Information Base(s)--FIB(s)--and the effects of currently-implemented aggregation schemes on FIB size. The conditions for reduction of FIB information before insertion into the kernel are considered, with preservation of routing a primary criteria (essentially deriving in a more structured manner the result that one wishes to remove extraneous routing information extant in the FIB(s)). Finally, aggregation algorithms consistent with these conditions are presented.