Ethernet is defined by the IEEE 802 standards. These are available for free through the IEEE GET Program, but you must login with an IEEE account. Here's a copy-paste from the 802 "Overview and Architecture" document, Chapter 8 (MAC addresses):
... the least significant bit (LSB) of the first octet is the individual/group (I/G) address bit. The next-to-LSB of the first octet for the assignment is the universal/local (U/L) address bit.
As waza-ari noted, Wireshark uses the alternative "LG" notation for the U/L bit.
The I/G address bit is used to identify the destination MAC address as an individual MAC address or a group MAC address. If the I/G address bit is 0, it indicates that the MAC address field is an individual MAC address. If this bit is 1, the MAC address is a group MAC address that identifies one or more (or all) stations connected to the IEEE 802 network. The all-stations broadcast MAC address is a special group MAC address of all 1’s
The U/L bit indicates whether the MAC address has been assigned by a local or universal administrator. Universal addresses have the U/L bit set to 0. If the U/L bit is set to 1, the remaining bits (i.e., all bits except the I/G and U/L bits) are locally administered and should not be expected to meet the uniqueness requirement of the IEEE RA-assigned values.
When U/L (LG) is set to 0, the first 3 octets (24 bits) of a MAC address are known as an OUI (Organisationally Unique Identifier). As you can see in your screenshot, Wireshark looks up the OUI in a table maintained by the IEEE Registration Authority (also freely available) and displays the organisation name. In this case 0x0017C4 = "Quanta Microsystems, INC."
When U/L (LG) is set to 0, the MAC address must be globally unique. When U/L (LG) is set to 1, the MAC address must be LOCALLY unique. i.e. The uniqueness does not need to extend beyond a router.
So, waza-ari is wrong in one respect: the U/L (LG) bit is important.
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