Going for CCENT, need help with a practice exam

Unanswered Question
Jul 20th, 2010

I'm doing a Boson practice exam and I started out as pretty confident, but right on question 1, even the correct answer explanation doesn't make sense to me. I'm going to post questions I don't understand as I go on with the exam. Any help would be appreciated.

Question 1

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Clipboard-2.jpg

A. PC2 sends an ARP broadcast looking for PC3, and PC3 replies.

B. R1 forwards two frames ont the LAN: one with PC2's MAC address as the destination and the other with PC3 MAC address as the destination.

C. PC1 sends two ARP request, one for PC2 and one for PC3 but only PC2 replies.

D. PC3 replies to an ARP request from PC1 with an ARP reply, and PC2 sends any frame.

I chose A, but the correct answers are A and D here is the explanation from the exam.

"Addresses are added to the MAC address table based on a switch receiving a frame and the switch examining the frame's source MAC address. In any case, as long as PC2 sends a frame, SW2 learns its MAC address. When PC3 sends a frame and SW2 receives it, SW2 adds an entry in its MAC address table for PC3."

Here is my logic. Looking at the diagram, everything seems to be in the same LAN with correct mask and default gateway. Everything should be able to communicate with each other which is why I chose A and not C. For B, I suppose that if the MAC address of PC2 and PC3 are not in the CAM table of any switch, R1 probably doesn't know what their MAC address is, so I did not choose B. However, it seems to me that it is possible that R1 could somehow have PC2 and PC3's MAC addresses in its cache if for example, the network could have started with an old switch which has been replaced by those 3 switches just a nanosecond before this network was built. A quick google search tells me that an ARP cache expires in 10 mins, which is very long. B seems ambiguous. As for the D, I understand PC3 can ARP reply to PC1, but what exactly does "PC2 sends any frame" mean?

Also, the explanation doesn't make sense to me neither. I understand the whole thing about how switches forward frames, or at least I think I do. The questions asked doesn't seem to be relevant at all with concepts about switch frame forwarding.

I will surely post more questions as I go. Any help is appreciated. Thanks.

Question 14

I have to admit that this question got me fair and square. SW1 is connected to Hub1. SW2 is connected to Hub1. No other links are on Hub1. Can the communication from SW1 to Hub1 be full duplex? I answered yes since I reasoned that hubs are Layer 1 devices and simply regenerate electric signals. I thought only PCs can send jamming signals due to a collision while hubs and switches cannot. I'm not sure where I got it wrong though. Is it that switches can also send jamming signals? Is it simply another reason? On a side note, can the communication be full duplex if the hub was only a repeater? What if it was a bridge? Those devices sound like they could support full duplex, but can anyone confirm?

I have this problem too.
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jimmysands73_2 Tue, 07/20/2010 - 15:06

I never could find the question for #1!!   And also, you will get alot of support at the CCENT found on the Cisco Learning Network....I consider this fourm real world and the CLN as a labs/student fourm....those you will see both on both fourms.

Whats the question for #1?

CCENT fourm on CLN: https://learningnetwork.cisco.com/community/certifications/ccent?view=all

https://learningnetwork.cisco.com/community/certifications/ccent

feng.lian Tue, 07/20/2010 - 17:53

Okay thanks. I will try those links. I didn't know there was a forum dedicated to each exam.

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