摘要：B
iologists believe that human life is limited by the number of
times cells can replicate; noncancerous cells have a kind of
internal counter that prevents them from replicating forever.
Even if humans are kept healthy in every respect, they will eventually
die simply because their cells will cease to replicate. Internet routers
also have a fnite lifetime. They are built with a fxed amount of hard-
ware memory for storing the forwarding table (the memory structure
that tells the router where to forward any IP packet, also called the
Forwarding Information Base [FIB]). As the Internet global routing
table grows, it eventually overfows the FIB, and the router ceases to
be able to hold the full routing table. Even if the router is healthy in
every respect (all of its hardware components still operate), it can no
longer function as a router in the Internet Default-Free Zone (DFZ),
where no default routes can be used.
