Switch, MAC Addresses, ARP
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I am really baffled by this question. Shouldn't the answer be B. The destination MAC address is already listed in the MAC address table, so it shouldn't have any problems forwarding it onto its destination. Why is the answer D? Wouldn't the switch only do this if the destination MAC address is not on the MAC address table yet?
^^^image removed by moderator^^^ (image was posted of a mac address table) -
Jamie,
Let's ignore the specific question and focus on the fundamentals which you know. I'll tell you why after we go over the fundamentals first. So before I begin your understanding of the fundamentals is where they need to be.
Remember, that a switch will either forward, flood or filter the frame based on MAC address, specifically the destination MAC address. Three rules then:
1. If a switchport receives a frame, it compares the destination MAC on the frame to the MAC address table. If it finds the matching MAC, it forwards it to the port associated with the MAC address in the table.
2. If the switchport receives a frame, it compares the destination MAC on the frame to the MAC address table. If the MAC address is either: a broadcast MAC (ff-ff-ff-ff-ff-ff) or an unknown unicast (not yet in the address table) then the switch has to flood the received frame out every other port except the one it arrived on. This gives it the best chance of getting the frame to the destination if the destination hasn't yet reported a MAC to the switch.
3. If the switchport receives a frame, it compares the destination MAC on the frame to the MAC address table. If the MAC address on that frame matches a MAC address in the table AND the destination port is the same as the port it was received on, the switch will filter it because a switch cannot forward the data out of the port it arrived on.
Ok, so why am I on purpose ignoring the specific question. Firstly, according to Cisco the usage of brain dumps is prohibited, even for study purposes. If you're wondering how I knew, well it's the word 'brain dump' watermarked on the pic! Your logic, in what you explained, was correct. Do the same without the brain dump on the exam, and do it quickly, the exam will not be problem for you...but you must do it quickly. Secondly, this shows you the hazards that you run into. Some of these "study materials" are not correct. In other words, it may lead you to have to verify that the answer is correct and this leads to more frustration.
So I cannot really answer this question directly in this way because that would be violating Cisco's policy. Also, this is not to say you're not allowed to post here; you are. But we cannot answer brain dump questions. I'm also going to edit your post of the picture so that we are not violating Cisco policy! Please feel free to post questions here though, that we welcome!
Cordially,
Ronnie Wong
Host, ITProTV -
Hey Ronnie,
Sorry about all that. I didn't know Brain Dumps was a violation of Cisco policy. Brother-in-law recommended it as good study material. I'm finding that not to be the case though. It's making me question stuff I learned from you and Don that I know is true! Anyways, thanks for the reply. Sorry once again. -
Jamie,
No need for apologies. We understand.
We know that a way to pass the exam is to use brain dumps. The exam though doesn't prove you know what to do or how to do it. It proves you know the exam. When an employer assigns you work on the technology and you don't understand it even though you passed the certification, this is the problem. This is when the certification loses value.
There is no better moment than when you earn your CCNA because you know the technology. It's worth the time you put into it!
Cordially,
Ronnie Wong
Host, ITProTV