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Switching Function

After the router has determined the exit interface using the path determination function, the router needs to encapsulate the packet into the data link frame of the outgoing interface.

The switching function is the process used by a router to accept a packet on one interface and forward it out another interface. A key responsibility of the switching function is to encapsulate packets in the appropriate data link frame type for the outgoing data link.

What does a router do with a packet received from one network and destined for another network? The router performs the following three major steps:

1. Decapsulates the Layer 3 packet by removing the Layer 2 frame header and trailer.

2. Examines the destination IP address of the IP packet to find the best path in the routing table.

3. Encapsulates Layer 3 packet into a new Layer 2 frame and forwards the frame out the exit interface.