- A. Layer 2 frame header and trailer
- B. Layer 3 IP address
- C. Layer 5 session
- D. Layer 4 protocol
Router Switching Function (18.104.22.168) A primary function of a router is to forward packets toward their destination. This is accomplished by using a switching function, which is the process used by a router to accept a packet on one interface and forward it out of 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.
In this context, the term “switching” literally means moving packets from source to destination and should not be confused with the function of a Layer 2 switch.
After the router has determined the exit interface using the path determination function, the router must encapsulate the packet into the data link frame of the outgoing interface. 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:
Step 1. De-encapsulates the Layer 3 packet by removing the Layer 2 frame header and trailer.
Step 2. Examines the destination IP address of the IP packet to find the best path in the routing table.
Step 3. If the router finds a path to the destination, it encapsulates the Layer 3 packet into a new Layer 2 frame and forwards the frame out the exit interface.