Switch Learning Vs. Switch Forwarding Question

certskills
By certskills May 2, 2014 09:05

For #CCENT and #CCNA, you need to know how switches learn, plus you need to know how switches forward frames. Sometimes, combining the two concepts (learning and forwarding) for the first time causes some mental hurdles.

In today’s post, we’ll use one of the questions from my ICND1 Cert Guide as a backdrop to work through these same concepts. The question weaves together learning and forwarding. Today’s post poses the question, while the next post works through the logic.

The Diagram

Figure 1: Diagram Used with this Question

The Question

The switch begins with no dynamically learned MAC addresses. The PC1 creates and sends a frame with a destination address of 2222.2222.2222. Then PC3 creates and sends a frame destined for PC2’s MAC address of 2222.2222.2222. Which of the following are true about this second frame? (Select all answers that are correct.)

The Possible Answers

A.      The switch discards (filters) the frame.

B.      The switch forwards the frame out of interface Fa0/1

C.      The switch forwards the frame out of interface Fa0/2

D.      The switch forwards the frame out of interface Fa0/3

Answer: Overlapping Connected and Routing Protocol Routes
Switch Learning Vs. Switch Forwarding - Analysis
certskills
By certskills May 2, 2014 09:05
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7 Comments

  1. Toigonbai May 2, 14:58

    C. The switch forwards the frame out of interface Fa0/2

    Reply to this comment
    • bars_dnb May 7, 07:46

      After PC1’s frame switch only learned PC1’s MAC (if there was no reply from PC2, which is not implied i guess). So when PC3 sends a frame destined for PC2’s MAC – switch doesn’t know where to send a frame, so it sends it out of all up interfaces except incoming. Answers: B and C.

      Reply to this comment
      • artem718 March 5, 10:59

        the answer is C because the first frame would be flooded out all the ports except the f0/1, 2nd frame will be forwarded out of f0/2 because the CAM table has learned the mac addresses of
        PC1 and PC2

        Reply to this comment
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