MAC address table question

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May 8th, 2009
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Doing some testing, a question came up asking me to consider each multiple choice and decide which one(s) will have the end result of PC2 and PC3 being in SW2's MAC address table.



The diagram which also includes the exhibit (show's output) are found here (public URL/no login):



http://www.facebook.com/photo.php?pid=2652380&l=d56dea0cf3&id=502714417



I understand both B and D are correct answers, but I also thought that C would be a correct answer.



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Jon Marshall Fri, 05/08/2009 - 06:29
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Erik


C is not a correct answer because a switch learns which mac-address is tied to which port based on the source mac-address in the frame. So in C all SW2 would learn is that R1's mac-address is on fa0/4.


Jon

godinerik Fri, 05/08/2009 - 06:43
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But since the router communicates with those two PCs, wouldn't it have to at some point send an ARP broadcast using their IP to find out their MAC address before it can deliver an ethernet frame to each of those hosts?

Jon Marshall Fri, 05/08/2009 - 06:50
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Erik


I don't disagree with what you are saying but whereas 2 & 4 will result in SW2 learning the mac-addresses of PC2 & PC3 answer 3 does not result in this, rather you have to assume that something else has happened first.


What if for example you entered static entries in the arp table on R1 ?


Jon

godinerik Fri, 05/08/2009 - 07:07
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I see now, I wasn't paying enough attention on the keywords. I said it myself, the question is "which situation WILL RESULT" and perhaps those were the two key words.



Thanks,



Erik

Jon Marshall Fri, 05/08/2009 - 07:17
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Erik


No problem. A lot of Cisco questions are like this, a bit ambiguous.


Jon

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