The main device that is discussed at the Network
layer is the router. Routers actually operate at
Layer 1 (bits on the medium at
router interfaces), Layer 2 (frames switched from one interface to another), based on packet information and
Layer 3 (routing decisions).
Packet flow
through routers
(i.e. selection of best path and actual switching to the proper output port) involves the use of Layer 3 network addresses. After the proper port has been selected, the router encapsulates the packet in a frame again to send the packet to its next destination. This process happens for every router in the path from the source host to the destination host.
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