Why must a MAC address be unique for every NIC produced?

April 21, 2015 at 05:17:21
Specs: Windows 7
Why must a MAC address be unique for every NIC produced? What effect will it have on the network if two devices from two different manufacturers share the last 24 bits of their MAC addresses?

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April 21, 2015 at 06:16:47
You can test that easily. Setup 2 VM's with identical MAC addresses and see what happens. Every time MAC addresses is send-out, the 2 NIC's will try to answer. This will result in lots of collisions with retries till one NIC get's to answer first. The Frame may not be intended for the one receiving it so lots of retries etc.. It looks like you have a very bad internet (Ethernet) connection.

If you have identical MAC in DIFFERENT (local LAN) networks, there is no problem.

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April 21, 2015 at 07:14:48
Question asked Sounds like its more of a homework question.


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April 21, 2015 at 17:33:12
Imagine it this way. Try delivering a package to an address where there is the same number twice on the same street.


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May 13, 2015 at 23:29:04
MAC addresses are the Layer 2 addresses of networking hardware. Similar to how Layer 3 addresses (IP addresses) work.

They are unique to the device from the manufacture - The first 6 characters of the MAC can identify the manufacture and the last 6 of the MAC is individual to the hardware.

If two devices have the same MAC address, a very similar issue would occur as if there were two computers that have the same IP address. Except you wouldn't notice this error at first, it is handled at the switch level (Layer 2) and would not present itself to the operating system. There would be lost packets/network connectivity to one or both computers.

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July 4, 2015 at 08:06:48
In a local network, hosts need to know the physical (MAC) addresses of the devices they want to communicate with. When your computer wants to communicate with another computer on the network, it first needs to run the Address Resolution Protocol (ARP) process in order to determine the MAC address of the device with the destination IP. If two devices have the same MAC address, both will inform your host that they have that MAC address, which can of course lead to unwanted consequences. More info: http://ccna-study-guide.com/address...

message edited by ShouldAt3

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July 17, 2015 at 08:29:38
I agree with XPuser, go to Wikipedia or just google your question. Every network card, or networked device has a unique MAC address for identification. Consider the MAC address as a house address. When information is sent (in packets), then it is directed to the correct device. If not, then devices would communicate with the wrong device. This creates a mess. Consider this simple example. Imagine you are talking with two people and both have the same name. One of them is going to think your are talking to them, when you are actually talking to the other person.

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