Document No. 10-300077, Issue 2 1-23
Introduction
■Since layer 2 modules have no routing capability, packets that are
received by a layer 2 module and require routing are forwarded by
sending the packet to the 50-series layer 3 or 80-series supervisor
module. The routing engine on the supervisor module t hen perf orms
the routing operation for the layer 2 modules and sends the packet
back through the switching fabric to the destination port.This is
referred to as the FORE path, or Fast Ou t of Bands Routing Engine,
since the routing is accomplished i n the hardware of either
supervisor module.
Figure 1-3 shows how traffic is routed in a switch.
Figure 1-3. Layer 2 and Layer 3 Routing in a Switch