MACosoite

MACosoite, known in Finnish as MAC-osoite, is the unique hardware identifier assigned to network interfaces for communications on the data link layer of a computer network. It is typically burned into the device by the manufacturer, though many systems allow software-based modification or spoofing. MAC addresses are used to deliver frames within a local network segment and are not meant to be routable across the Internet.

Format and structure: Most MAC addresses are 48 bits long, expressed as six hexadecimal octets. Common representations include 01:23:45:67:89:ab or 01-23-45-67-89-ab; some contexts also show them without separators. The first octet contains two significance bits: the I/G (individual/group) bit indicates unicast (0) or multicast (1); the U/L (universally/local) bit indicates globally unique (0) or locally administered (1). The first three octets form the Organizationally Unique Identifier (OUI), assigned to a manufacturer by IEEE; the remaining three octets identify a particular NIC within that vendor’s assignment.

Use and scope: MAC addresses enable Ethernet and other link-layer technologies to forward frames, manage access in switches, and support address resolution protocols such as ARP (IPv4) and Neighbor Discovery (IPv6). They are typically only meaningful within the same broadcast domain.

Security and privacy: Because a MAC address can identify a device, some platforms support randomization of MAC addresses when connecting to wireless networks to protect privacy. Conversely, MAC filtering and spoofing are potential security considerations on local networks.