1. A router for interconnecting external devices coupled to said router, said router comprising: a switch fabric; a plurality of routing nodes coupled to said switch fabric, wherein each of said plurality of routing nodes is capable of transmitting data packets to, and receiving data packets from, said external devices and is further capable of transmitting data packets to, and receiving data packets from, other ones of said plurality of routing nodes via said switch fabric; and a control processor capable of comparing the N most significant bits of a first subnet address associated with a first external port of a first routing node with the N most significant bits of a second subnet address associated with a second external port of said first routing node and, in response to the comparison, determining a P-bit prefix of similar leading bits in said first and second subnet addresses, wherein said control processor distributes said P-bit prefix to other ones of said plurality of routing nodes.