LAA (Locally Administered Address)

Addresses can either be universally administered addresses (UAA) or locally administered addresses (LAA). A universally administered address is uniquely assigned to a device by its manufacturer. The first three octets (in transmission order) identify the organization that issued the identifier and are known as the organizationally unique identifier (OUI).

The remainder of the address (three octets for EUI-48 or five for EUI-64) are assigned by that organization in nearly any manner they please, subject to the constraint of uniqueness. A locally administered address is assigned to a device by a network administrator, overriding the burned-in address.

Universally administered and locally administered addresses are distinguished by setting the second-least-significant bit of the first octet 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. If it is 1, the address is locally administered.

In the example address 06-00-00-00-00-00 the first octet is 06 (hex), the binary form of which is 00000110, where the second-least-significant bit is 1. Therefore, it is a locally administered address. Another example that uses locally administered addresses is the DECnet protocol.

The MAC address of the Ethernet interface is changed by the DECnet software to be AA-00-04-00-XX-YY where XX-YY reflects the DECnet network address xx.yy of the host. This eliminates the need for an address resolution protocol since the MAC address for any DECnet host can be simply determined.

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