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Exam 100-105 Question id=540 Routing Fundamentals

When a router makes a routing decision for a packet that is received from one network and destined to another, which portion of the packet does it replace?

A. Layer 2 frame header and trailer
B. Layer 3 IP address
C. Layer 5 session
D. Layer 4 protocol
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Explanation:
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.
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