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regarding the MAC U/L bit

Discussion in 'Network+' started by brandonn, Mar 28, 2014.

  1. brandonn

    brandonn New Member

    From wikipedia

    Universally administered and locally administered addresses are distinguished by setting the second-least-significant bit of the most significant byte of the address. This bit is also referred to as the U/L bit, short for Universal/Local, which identifies how the address is administered. If the bit is 0, the address is universally administered

    What does it mean to be a universally administered address? How does that function in the network?

    Same questions for locally administered addresses.
  2. The Zig

    The Zig Kilobyte Poster

    Excuse very late reply. Honestly, you don't need to worry about this. What it basically means:-

    "Universally administered" means the MAC address was burned into the device at manufacture. First half is the Manufacturer ID (so will be the same across many devices made by the same company), last half is device ID, which is unique to the device.
    This means it is globally unique. No two devices in the world will have the same MAC. It is universally controlled and guaranteed to be unique.

    "Locally administered" means someone came along and overrode the global one with something of their own. The stuff about 2-least significant bit just explains that if you're doing this, the binary has to look the right way. Some things force you to start the MAC 02-... to meet this requirement.

    In my experience, in the places I've been, no one's tinkered with the MACs. For the most part, these work just fine without user intervention.
    Certifications: A+; Network+; Security+, CTT+; MCDST; 4 x MTA (Networking, OS, Security & Server); MCITP - Enterprise Desktop Support; MCITP - Enterprise Desktop Administrator; MCITP - Server Administrator; MCSA - Server 2008; MCT; IOSH; CCENT
    WIP: CCNA; Server 2012; LPIC; JNCIA?

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