Understanding, Configuring, and Troubleshooting CEF
Understanding Router Pieces and Parts
Consider the following components required to switch a packet:
• Some device detects packets that the router needs to receive (pick up off the wire) and process.
• The packet needs to be stored (copied someplace in the router’s memory).
• The packet’s header must be examined (by the local packet psychologist to see whether the packet is
crazy), various options and fields within the packet (such as the Time to Live field) must be processed,
and the Layer 2 header needs to be replaced with the correct Layer 2 header for the next hop of the
packet’s journey.
• The packet must then be given to some device on the outbound interface that will transmit it onto the
correct network segment.
Each of these four steps must be performed by some piece of hardware or software within the router.
Most routers use the following fundamental pieces of hardware while switching packets: