Confused here by this question

Jasiono

This is from Odom's book, DO I ALREADY KNOW THIS.

PC1, with MAC address 1111.1111.1111, is connected to Switch SW1’s Fa0/1 interface. PC2, with MAC address 2222.2222.2222, is connected to SW1’s Fa0/2 interface. PC3, with MAC address 3333.3333.3333, connects to SW1’s Fa0/3 interface. The switch begins with no dynamically learned MAC addresses, followed by PC1 sending a frame with a destination address of 2222.2222.2222. If the next frame to reach the switch is a frame sent by PC3, destined for PC2’s MAC address of 2222.2222.2222, which of the following are true? (Choose two answers.)

• a. The switch forwards the frame out interface Fa0/1.
• b. The switch forwards the frame out interface Fa0/2.
• c. The switch forwards the frame out interface Fa0/3.
• d. The switch discards (filters) the frame.

The book has it as answers A and B

Jasiono

From my understanding, when PC1 sends a frame destined for PC2, and the switch has no CAM table, the switch will forward the frame out on all ports with the exception of the one it received the frame from.
While it does that, it adds the MAC address of PC1 into the table.

I think I answered my own question now. I'm assuming that since PC2 did not reply back to PC1, the MAC address of PC2 is still unknown, causing the switch to send the frame sent by PC3 out on FA0/1 and FA0/2. While it does that, it adds the MAC address of PC3 into it's table.

The end result, considering PC2 has not sent anything to anyone in the form of a reply or whatever, it only knows the MAC address of PC1 and PC3.


Is this how the questions are on the exam? I really had to think about that one.

Jon_Cisco

It's not possible to say what the test questions will be but this is a good example of figuring out the logic. If you were not told to choose two than you probably would have ignored the part of the question that indicated the next frame to his the switch. It implies that PC2 has not responded so the address is not yet known.

The questions on the CD that came with the book also come with the answers. Don't read the answers until you reread the questions you got wrong. Think about it then read the answers. This will help you remember the context to the questions as well as just memorizing the answers.

When I started retaking the same questions I talked myself through why each answer was right or wrong. Because it becomes all to easy to remember what the answer was for each question. But memorizing the answers rather then the context is a mistake.

Good Luck!

Jasiono

Thanks

That's what I did. I always take the DO I ALREADY KNOW THIS and quickly compare my answers, and I attempt to figure out why I was wrong and looks for an explanation while reading the chapter. It's helped me.

I think from now on what I will do is look at every answer when taking any sort of practice exam and telling myself why an answer is either right or wrong.

Hondabuff

Jasiono wrote: »

This is from Odom's book, DO I ALREADY KNOW THIS.




The book has it as answers A and B

I'm confused by this empty post. Also your post count is 666 so you better fix it.

Jasiono

PC1, with MAC address 1111.1111.1111, is connected to Switch SW1’s Fa0/1 interface. PC2, with MAC address 2222.2222.2222, is connected to SW1’s Fa0/2 interface. PC3, with MAC address 3333.3333.3333, connects to SW1’s Fa0/3 interface. The switch begins with no dynamically learned MAC addresses, followed by PC1 sending a frame with a destination address of 2222.2222.2222. If the next frame to reach the switch is a frame sent by PC3, destined for PC2’s MAC address of 2222.2222.2222, which of the following are true? (Choose two answers.)

• a. The switch forwards the frame out interface Fa0/1.
• b. The switch forwards the frame out interface Fa0/2.
• c. The switch forwards the frame out interface Fa0/3.
• d. The switch discards (filters) the frame.

Is it visible now? And thanks for the heads up on the post count haha.

Hondabuff

I liked it better when it was blank

theodoxa

Sequence of Events --

1) PC1 Sends a Frame to PC2
2) SW1 doesn't know how to reach PC2, so it floods the frame out all ports (Fa0/2 and Fa0/3) except the port (Fa0/1) on which it was received and records the MAC Address, Port, and VLAN Assignment for PC1.
3) Before, PC2 can send a response to PC1, SW1 receives a frame from PC3 destined for PC2
4) Since PC2 has not sent any traffic yet, SW1 still doesn't know how to reach it, so it floods the frame out all ports (Fa0/1 and Fa0/2) except the port (Fa0/3) it was received on and records the MAC Address, Port, and VLAN Assignment for PC3.
5) Assuming PC2 is up and working, it should eventually respond to PC1. When SW1 receives this frame, it will know where PC1 is (since it recorded that information when it received the original packet from PC1) and will only forward that frame out the port that PC1 is on. SW1 will also finally record the MAC Address, Port, and VLAN Assignment of PC2.