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Duplicate MAC Address

Discussion in 'Network+' started by Shinigami, Oct 6, 2009.

  1. Shinigami

    Shinigami Megabyte Poster

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    So I started reading the latest Meyers book for this exam (nice book btw, easy to read, friendly text) and came upon this one page where the author stresses that "No two NICs ever share the same MAC address—ever" (his words).

    Now, maybe in a perfect world, but I have personally seen two instances of conflicting MAC addresses in the past 10 years and a quick google search shows that I was not alone (after all, if a manufacturer is allocated a single batch of addresses to distribute, they can only burn 16 million MAC's before they run out and need another pool for their company ID, and of course there's more that 16 million network cards in circulation from the more popular companies).

    But anyway, I was just wondering if anyone else has ever encounteres a duplicate MAC address that was genuinely duplicated (and most likely an error from the company who made the chipset)?
     
    Last edited: Oct 6, 2009
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  2. craigie

    craigie Terabyte Poster

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    Yep, I have encountered a duplicate MAC Address, one was on a Wyse Terminal and the other on a Printer.

    Strange but true.
     
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  3. BosonMichael
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    BosonMichael Yottabyte Poster

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    I've only encountered duplicates that were manually reprogrammed - I once had some NICs that I could manually readdress.
     
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  4. Shinigami

    Shinigami Megabyte Poster

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    That's bizarre, so the terminal and printer had NIC's built by the same manufacturer then.

    I had this happen with two 3com network cards back in 99/2000, and once in 03 when doing RRAS tests (if I recall correctly) in a lab environment with mobo mounted NIC's. The training center had to replace one of the workstations after we spent a frustrating half an hour trying to get the test from crapping out :\
     
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  5. BosonMichael
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    BosonMichael Yottabyte Poster

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    I believe the programmable NICs I had were 3Coms.
     
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  6. Sparky
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    Sparky Zettabyte Poster Moderator

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    Never seen it before but somebody I worked with a few years ago mentioned they had stumbled across a duplicate mac address problem.
     
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  7. soundian

    soundian Gigabyte Poster

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    I imagine they give the manufacturers a block of IDs. After all, there's 16 million company IDs to dish out so giving one manufacturer a block of 3000 won't make much of a dent in that figure but would mean they could manufacture one device for pretty much everyone alive that's capable of using devices.
    Although the insertion of a "should" in that sentence from Mr Meyers would make sense.
     
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