A trie is simply a method of arranging IP addresses that assists in locating a route with a minimal number of steps.
Because IP network transactions usually result in a stream of packets, it is a reasonable assumption that after a packet to a particular destination has been switched, another is likely to arrive in the near future.
By building a cache of recently switched destinations, there are considerable savings in full route table lookups for subsequent packets to the same destinations. Moreover, other information that is required for the MAC header rewrite can be stored in the cache, rather than being recalculated. This arrangement is called fast switching; it is the default switching mechanism on all Cisco router platforms. Fast switching reduced the CPU utilization associated with packet switching and boosted the performance of the AGS to 20,000 pps.
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