In the design of contemporary core routers, table maintenance and packet
processing are discrete functions.
The maintenance of comprehensive routing information that includes a superset of
best paths is common practice, with proven benefits. However, it is neither
necessary nor desirable to consult this database for a forwarding decision.
Instead, the fastpath need only have knowledge of the best next hop matching a
DA prefix.
Whatever changes we believe to be in store for the table population, this is
unlikely to affect the typical number of adjacencies for a core router. Assuming
also that we continue to use IPv4 for a while, the "input length" of composite
information for the FIB could be less than 7 bytes for unicast routes. For the
2.5E5 best paths discussed, this equates to approximately 1.4MB.
Also, since the matching (ideally) yields a singular, exclusive result, this
matching operation is easily "parallelized" , in hardware or otherwise; observed
work need not even be linear with FIB size.
In short, the technical obstacles presented by high table / route population are
no greater for forwarding logic than for the control plane.
Regards,
Andrew Bender
Total Network Solutions, Inc.