Editing MAC address (section)

===Unicast vs. multicast (I/G bit)===

The least significant bit of an address's first octet is referred to as the ''I/G'', or ''Individual/Group'', bit.<ref name="mac-bit-field-names" />{{Self-published inline|date=November 2022}}{{Ref RFC|4291}}{{rp|p=20}} When this bit is 0 (zero), the [[frame (networking)|frame]] is meant to reach only one receiving [[network interface controller|network interface]].<ref>{{cite web|url=https://standards.ieee.org/wp-content/uploads/import/documents/tutorials/fibre.pdf|title=Guidelines for Fibre Channel Use of the Organizationally Unique Identifier (OUI)|publisher=IEEE-SA|access-date=2018-10-11}}</ref> This type of transmission is called [[unicast]]. A unicast frame is transmitted to all nodes within the [[collision domain]]. In a modern wired setting (i.e. with ''[[Network switch|switches]]'', not simple ''[[Ethernet hub|hubs]]'') the collision domain usually is the length of the Ethernet cabling between two network interfaces. In a wireless setting, the collision domain is all receivers that can detect a given wireless signal. If a [[network switch|switch]] does not know which port leads to a given MAC address, the switch will forward a unicast frame to all of its ports (except the originating port), an action known as [[unicast flood]].<ref>{{Cite web|url=https://supportforums.cisco.com/document/68421/overview-layer-2-switched-networks-and-communication|title=Overview of Layer 2 Switched Networks and Communication {{!}} Getting Started with LANs {{!}} Cisco Support Community {{!}} 5896 {{!}} 68421|website=supportforums.cisco.com|access-date=2016-05-17|date=2011-07-23}}</ref>{{Self-published inline|date=November 2022}} Only the node with the matching hardware MAC address will (normally) accept the frame; network interfaces with non-matching MAC-addresses ignore the frame unless they are in [[promiscuous mode]].

If the least significant bit of the first octet is set to 1 (i.e. the second hexadecimal digit is odd) the frame will still be sent only once; however, network interface controllers will choose to accept or ignore it based on criteria other than the matching of their individual MAC addresses: for example, based on a configurable list of accepted multicast MAC addresses. This is called [[multicast]] addressing.

The IEEE has built in several special address types to allow more than one [[Network Interface Card|network interface card]] to be addressed at one time:
* Packets sent to the [[broadcast address]], all one bits, are received by all stations on a local area network. In [[hexadecimal]] the broadcast address would be {{MACaddr|FF:FF:FF:FF:FF:FF}}. A broadcast frame is [[flooding (computer networking)|flooded]] and is forwarded to and accepted by all other nodes.
* Packets sent to a [[multicast address]] are received by all stations on a LAN that have been configured to receive packets sent to that address.
* '''Functional addresses''' identify one or more Token Ring NICs that provide a particular service, defined in IEEE 802.5.

These are all examples of ''group addresses'', as opposed to ''individual addresses''; the least significant bit of the first octet of a MAC address distinguishes individual addresses from group addresses. That bit is set to 0 in individual addresses and set to 1 in group addresses. Group addresses, like individual addresses, can be universally administered or locally administered.