CCENT Question 102: Switch MAC Learning

 In CCENT-OLD, Q&A

Here’s another #CCENT question that kicks up a small notch. PC1 successfully connects to a web server. What MAC address table entries are learned? To answer, you have to think about not just layer 2, but also layer 3, and even a tad bit about layer 4.

The Scenario: Question 102

I’ve numbered some of these questions just for my own long-term self-defense of keeping track of what’s what. This question, numbered 102, uses the same figure as the previous question. However, to focus on the ideas, instead of trivia, it shows each device’s MAC address as a pseudo-MAC address (eg, PC1-MAC for PC1’s MAC address).

Figure 102: Network Used for Question 102

Question

The user at PC1 opens a web browser and successfully connects to the web server hosted at PC4. None of the switches use port security, and none of the switches have statically configured any entries in their MAC address tables. All switch ports are configured to be in the default VLAN 1. Which of the following answers is true regarding the MAC table entries that should exist immediately after PC1 connects to the PC4 web server? (More than 1 correct answer may exist.)

a)     SW1: PC4-MAC, Port Fa0/1

b)     SW2: PC4-MAC, Port Fa0/5

c)     SW4: PC1-MAC, Port Gi0/2

d)     SW2: PC1-MAC, Port Fa0/4

 

Q101 Answer: Combining Protocols
CCENT Answer 102: Switch MAC Learning
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John B

If I type the command show mac address-table interface FastEthernet0/1 at SW1, I should see the MAC Address of PC1, in the real world lol

Scott Murphy

I believe the correct answers are: B,C,D

Michel

Yep B,C,D are the correct answers.

Oussama B

D

xcieja

A and D –
Why ?
PC1 and PC4 are in two different networks.

PC1 in order to send packet to PC4 sends frame to Def GW (R1).

PC1 sends frame to R1 -it arrives at SW1 -SW1 saves source MAC address.
Next it forwards frame to SW2 -> SW2 saves source MAC of PC1 and forwards frame to R1.

Please note that it doesn`t matter if SW1 and SW2 have already in MAC table MAC of R1 or they don`t have….

lyjo

Hi folks – nice comments! I’ll post answers Monday.

wertz

B,C,D

B – when PC1 initially try to connects to PC4, the switch realizes it can go out port 0/5 to get to PC4

C – To get back to PC1, the switches knows that it needs to go back out Port Gi0/2 to get back to PC1

D – Lastly SW2 knows to go out port 0/4 to get back to pc 1

A – The answer should be port 0/3

Hope im correct lol

J Want

My answer would be ‘D’

The other three in my opinion are wrong as they reference layer 2 addresses outside of the LAN (ie beyond a router). So PC4’s mac would never make it into the left side LAN and PC1’s mac wouldn’t make it into the right side LAN

I think…

[…] Today’ post gives the letter answer, and explains why, for this latest #CCENT question. The question focuses on switch learning, with a little layer 3 weaved in. Don’t read here until you try the question! […]

lyjo

Hi all – thanks for the discussions – Answer post is now available here!
http://www.certskills.com/ccent/ccent-answer-102-switch-mac-learning/

Wendell

Jim

Link to the answer page is not found –

404
We seem to have lost You in the clouds
The page You’re looking for is not here.
Maybe You should go home or try a search:

lyjo

Hi Jim,
Fixed. Thanks, W

[…] Today’ post gives the letter answer, and explains why, for this latest #CCENT question. The question focuses on switch learning, with a little layer 3 weaved in. Don’t read here until you try the question! […]

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