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In work, as in all things in life it takes a lot of professionalism, so much experience, so much flexibility, but also so much ass. With regard to ' have found two NICs with the same MAC address , someone asked me how I came to think about this problem.

I still remember, in the early 2000s, a course Cisco CCDA , the teacher spoke to us of personally experienced a similar experience where, on a complex enterprise network with hundreds of hosts had discovered, after two days of troubleshooting , a lot of network cards with the same MAC address.

He took us two days, as I only ever 20 minutes? Well, first of all my hosts were thirty and not hundreds but mostly because I had the ass and now I'll tell you how it went.

As I said call me because within this network LAN data transfer from a local computer to another goes in fits and starts.

To make the tests ask you to use two computers on the network on which to install iperf , a software that measures the performance of an IP connection between two computers. I simply place on a desk where there is a desktop computer and one laptop.

On the fixed IP address 10.100.0.100 active part of iperf server and do various tests with the laptop connecting me with the IP of the server, which is already a mnemonic address that is easy to remember, and if you repeat it several times, go to memory immediately.

Indeed, the well-known effect in fits and starts, but while I'm making several attempts to try to isolate the problem I get an employee of the company that makes me "Have you done anything to the INTERNET? Why can not I lose access to $ appViaWeb."

There I describe my face but imagine the usual to Davide Bianchi

davide_bianchi

But anyway I'm going to see. I feel the table that actually reaches the gateway. Ok, we see that the IP address of the computer has this nice employee. 10.100.0.100! Hey, it's the same computer that I was using as a server iperf.

Here we cat breeding. One of the two PCs set a static address? No, both of them have the configuration via DHCPd . Ok, there are two DHCPd in ​​the network? No, there is only one.

But then how the hell did you come to mind to you DHCPd to assign the same IP address on two different computers? Ipconfig / all and, hey, mac but this reminds me of something on this PC ... 34:56, 34:56 iperf on the server ... ok segnamoci the entire MAC 00: E0: 18:12:34:56 one part, 00: E0: 18:12:34:56 other, again calculate, control again, control again. Heck, but then the DHCPd not wrong because, for him, these two PCs are the same PC that you have seen with what, for him, is the same network adapter. But this is obviously bad for the entire network Layer 2 and for the poor switch you see, what for them is the same as the PC, once come to a door, and once by another. I guess ill test ...

In the end it just like that. Two NICs with the same MAC address. So huge ass in having used as a server for testing just one of the two PCs with network card "cloned" otherwise I think I would have gone mad in groped to solve the problem of this LAN.

I have pointed out that, apart from the part 00: E0: 18 that corresponds to the manufacturer Asustek, the remaining part is 123456.

How I solved it? Easily, I went to set up the driver of windows and I manually set the MAC address 00: E0: 18:12:34:5 7 on the second network card, and then I went looking for a PC of the same brand to see even if those network cards have the MAC cloned.

Note color, imagine the non-nerds who have seen this a fool to go back and forth to their company babbling all the time, "I do not believe it is not possible, is not it, I'm doing something wrong" while I drive -became convinced that he had found two NICs with the same MAC address.

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