The addresses are usually assigned by the hardware manufacturer, and these IDs are considered burned into the firmware of the network access hardware.

Because of this process, some vendors use specific formats in the hardware address.

The MAC address is a 12-digit hexadecimal number or 48 bits in length.

This address is assigned by the hardware manufacturer and is globally unique, so you should not have duplicate addresses on your network (although cards with duplicate addresses have been manufactured by production errors in the past).

This is a technique used by hackers to circumvent MAC-based security restrictions.

This is more common when using main frame systems that communicate via MAC addresses rather than protocol addresses (such as IP addresses).

The following table shows a list of the first 20 companies that have addresses registered.

Reviewing even the first few entries on the table, you notice some of those names as incumbent or early starters in the networking and computing world, including Xerox (which actually has the first ten registered numbers), Cisco, Fujitsu, and so on.

Hopefully, knowing that duplicate MAC addresses might happen, you may not dismiss it as an impossibility, which will allow you to identify the problem more quickly.

He holds the Cisco CCNA and numerous other certifications, and has provided system and LAN support to both large and small organizations.

Ed is coauthor of CompTIA A Certification All-in-One For Dummies.

What Is A Mac Address Used For