MAC address
Encyclopedia
A Media Access Control address (MAC address) is a unique identifier
assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802
network technologies, including Ethernet
. Logically, MAC addresses are used in the Media Access Control
protocol sub-layer of the OSI reference model.
MAC addresses are most often assigned by the manufacturer of a network interface card (NIC) and are stored in its hardware, the card's read-only memory, or some other firmware mechanism. If assigned by the manufacturer, a MAC address usually encodes the manufacturer's registered identification number and may be referred to as the burned-in address. It may also be known as an Ethernet hardware address (EHA), hardware address or physical address. A network node may have multiple NICs and will then have one unique MAC address per NIC.
MAC addresses are formed according to the rules of one of three numbering name spaces managed by the Institute of Electrical and Electronics Engineers
(IEEE): MAC-48, EUI-48, and EUI-64. The IEEE claims trademark
s on the names EUI-48 and EUI-64, in which EUI is an acronym for Extended Unique Identifier.
) format for printing MAC-48 addresses in human-friendly form is six groups of two hexadecimal
digits, separated by hyphens (-) or colons (:), in transmission order
(e.g.
01-23-45-67-89-ab
or
01:23:45:67:89:ab
).
This form is also commonly used for EUI-64. Another convention used by networking equipment uses three groups of four hexadecimal digits separated by dots (.) (e.g.
0123.4567.89ab
), again in transmission order.
MAC address comes from the original Xerox
Ethernet addressing scheme. This 48-bit address space contains potentially 248 or 281,474,976,710,656 possible MAC addresses.
All three numbering systems use the same format and differ only in the length of the identifier. Addresses can either be universally administered addresses or locally administered addresses. A universally administered address is uniquely assigned to a device by its manufacturer; these are sometimes called burned-in addresses. The first three octets
(in transmission order) identify the organization that issued the identifier and are known as the Organizationally Unique Identifier
(OUI). The following three (MAC-48 and EUI-48) or five (EUI-64) octets are assigned by that organization in nearly any manner they please, subject to the constraint of uniqueness. The IEEE expects the MAC-48 space to be exhausted no sooner than the year 2100; EUI-64s are not expected to run out in the foreseeable future. A locally administered address is assigned to a device by a network administrator, overriding the burned-in address. Locally administered addresses do not contain OUIs.
Universally administered and locally administered addresses are distinguished by setting the second least significant bit
of the most significant byte 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 most significant byte 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. Consequently, this bit is 0 in all OUIs.
If the least significant bit of the most significant octet of an address is set to 0 (zero), the frame is meant to reach only one receiving NIC
. This type of transmission is called unicast
. A unicast frame is transmitted to all nodes within the collision domain
, which typically ends at the nearest network switch
or router. Only the node with the matching hardware MAC address will accept the frame; network frames with non-matching MAC-addresses are ignored, unless the device is in promiscuous mode
.
If the least significant bit of the most significant address octet is set to 1, the frame will still be sent only once; however, NICs will choose to accept it based on different criteria than a matching MAC address: for example, based on a configurable list of accepted multicast MAC addresses. This is called multicast
addressing.
The following technologies use the MAC-48 identifier format:
The distinction between EUI-48 and MAC-48 identifiers is purely nominal: MAC-48 is used for network hardware; EUI-48 is used to identify other devices and software. (Thus, by definition, an EUI-48 is not in fact a "MAC address", although it is syntactically indistinguishable from one and assigned from the same numbering space.)
The IEEE now considers the label MAC-48 to be an obsolete term, previously used to refer to a specific type of EUI-48 identifier used to address hardware interfaces within existing 802-based networking applications, and thus not to be used in the future. Instead, the proprietary term EUI-48 should be used for this purpose.
EUI-64 identifiers are used in:
The IEEE has built in several special address types to allow more than one network interface card to be addressed at one time:
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.
In addition, the EUI-64 numbering system encompasses both MAC-48 and EUI-48 identifiers by a simple translation mechanism. To convert a MAC-48 into an EUI-64, copy the OUI, append the two octets FF-FF and then copy the organization-specified extension identifier. To convert an EUI-48 into an EUI-64, the same process is used, but the sequence inserted is FF-FE. In both cases, the process can be trivially reversed when necessary. Organizations issuing EUI-64s are cautioned against issuing identifiers that could be confused with these forms. The IEEE policy is to discourage new uses of 48-bit identifiers in favor of the EUI-64 system.
IPv6
— one of the most prominent standards that uses a Modified EUI-64 — treats MAC-48 as EUI-48 instead (as it is chosen from the same address pool) and toggles the U/L bit (as this makes it easier to type locally assigned IPv6 addresses based on the Modified EUI-64). This results in extending MAC addresses (such as IEEE 802 MAC address) to Modified EUI-64 using only FF-FE (and never FF-FF) and with the U/L bit inverted.
is a 24-bit OUI
managed by the IEEE Registration Authority, followed by 12 IEEE-provided bits (identifying the organization), and 12 bits for the owner to assign to individual devices. An IAB is ideal for organizations requiring fewer than 4097 unique 48-bit numbers (EUI-48).
Changing MAC addresses is necessary in network virtualization
. It can also be used in the process of exploiting security vulnerabilities. This is called MAC spoofing
.
A host cannot determine from the MAC address of another host whether that host is on the same link (network segment
) as the sending host, or on a network segment bridged to that network segment.
In TCP/IP networks, the MAC address of an interface can be queried knowing the IP address
using the Address Resolution Protocol
(ARP) for Internet Protocol
Version 4 (IPv4
) or the Neighbor Discovery Protocol
(NDP) for IPv6
. On broadcast networks, such as Ethernet, the MAC address uniquely identifies each node
on that segment and allows frames to be marked for specific hosts. It thus forms the basis of most of the Link layer
(OSI Layer 2) networking upon which upper layer protocols rely to produce complex, functioning networks.
However, the effect is not immediate (address learning).
Many higher-end switches currently in distribution are Layer 3 switches. Such a switch supports IP multicast and therefore uses the IP address for routing. The switch preserves the MAC address for compatibility but does not need to use it for routing.
/ifconfig
/ipconfig
command, for example.
However, since IEEE 802.3
(Ethernet) and IEEE 802.4 (Token Bus) send the bytes (octets) over the wire, left-to-right, with least significant bit in each byte first, while IEEE 802.5 (Token Ring) and IEEE 802.6
send the bytes over the wire with the most significant bit first, confusion may arise when an address in the latter scenario is represented with bits reversed from the canonical representation. For example, an address in canonical form
When the first switches supporting both Token Ring and Ethernet came out, some did not distinguish between canonical form and non-canonical form and so did not reverse MAC address bits as required. This led to cases of duplicate MAC addresses in the field.
Unique identifier
With reference to a given set of objects, a unique identifier is any identifier which is guaranteed to be unique among all identifiers used for those objects and for a specific purpose...
assigned to network interfaces for communications on the physical network segment. MAC addresses are used for numerous network technologies and most IEEE 802
IEEE 802
IEEE 802 refers to a family of IEEE standards dealing with local area networks and metropolitan area networks.More specifically, the IEEE 802 standards are restricted to networks carrying variable-size packets. IEEE 802 refers to a family of IEEE standards dealing with local area networks and...
network technologies, including Ethernet
Ethernet
Ethernet is a family of computer networking technologies for local area networks commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired LAN technologies....
. Logically, MAC addresses are used in the Media Access Control
Media Access Control
The media access control data communication protocol sub-layer, also known as the medium access control, is a sublayer of the data link layer specified in the seven-layer OSI model , and in the four-layer TCP/IP model...
protocol sub-layer of the OSI reference model.
MAC addresses are most often assigned by the manufacturer of a network interface card (NIC) and are stored in its hardware, the card's read-only memory, or some other firmware mechanism. If assigned by the manufacturer, a MAC address usually encodes the manufacturer's registered identification number and may be referred to as the burned-in address. It may also be known as an Ethernet hardware address (EHA), hardware address or physical address. A network node may have multiple NICs and will then have one unique MAC address per NIC.
MAC addresses are formed according to the rules of one of three numbering name spaces managed by the Institute of Electrical and Electronics Engineers
Institute of Electrical and Electronics Engineers
The Institute of Electrical and Electronics Engineers is a non-profit professional association headquartered in New York City that is dedicated to advancing technological innovation and excellence...
(IEEE): MAC-48, EUI-48, and EUI-64. The IEEE claims trademark
Trademark
A trademark, trade mark, or trade-mark is a distinctive sign or indicator used by an individual, business organization, or other legal entity to identify that the products or services to consumers with which the trademark appears originate from a unique source, and to distinguish its products or...
s on the names EUI-48 and EUI-64, in which EUI is an acronym for Extended Unique Identifier.
Notational conventions
The standard (IEEE 802IEEE 802
IEEE 802 refers to a family of IEEE standards dealing with local area networks and metropolitan area networks.More specifically, the IEEE 802 standards are restricted to networks carrying variable-size packets. IEEE 802 refers to a family of IEEE standards dealing with local area networks and...
) format for printing MAC-48 addresses in human-friendly form is six groups of two hexadecimal
Hexadecimal
In mathematics and computer science, hexadecimal is a positional numeral system with a radix, or base, of 16. It uses sixteen distinct symbols, most often the symbols 0–9 to represent values zero to nine, and A, B, C, D, E, F to represent values ten to fifteen...
digits, separated by hyphens (-) or colons (:), in transmission order
(e.g.
01-23-45-67-89-ab
or
01:23:45:67:89:ab
).
This form is also commonly used for EUI-64. Another convention used by networking equipment uses three groups of four hexadecimal digits separated by dots (.) (e.g.
0123.4567.89ab
), again in transmission order.
Address details
The original IEEE 802IEEE 802
IEEE 802 refers to a family of IEEE standards dealing with local area networks and metropolitan area networks.More specifically, the IEEE 802 standards are restricted to networks carrying variable-size packets. IEEE 802 refers to a family of IEEE standards dealing with local area networks and...
MAC address comes from the original Xerox
Xerox
Xerox Corporation is an American multinational document management corporation that produced and sells a range of color and black-and-white printers, multifunction systems, photo copiers, digital production printing presses, and related consulting services and supplies...
Ethernet addressing scheme. This 48-bit address space contains potentially 248 or 281,474,976,710,656 possible MAC addresses.
All three numbering systems use the same format and differ only in the length of the identifier. Addresses can either be universally administered addresses or locally administered addresses. A universally administered address is uniquely assigned to a device by its manufacturer; these are sometimes called burned-in addresses. The first three octets
Octet (computing)
An octet is a unit of digital information in computing and telecommunications that consists of eight bits. The term is often used when the term byte might be ambiguous, as there is no standard for the size of the byte.-Overview:...
(in transmission order) identify the organization that issued the identifier and are known as the Organizationally Unique Identifier
Organizationally Unique Identifier
An Organizationally Unique Identifier is a 24-bit number that is purchased from the Institute of Electrical and Electronics Engineers, Incorporated Registration Authority...
(OUI). The following three (MAC-48 and EUI-48) or five (EUI-64) octets are assigned by that organization in nearly any manner they please, subject to the constraint of uniqueness. The IEEE expects the MAC-48 space to be exhausted no sooner than the year 2100; EUI-64s are not expected to run out in the foreseeable future. A locally administered address is assigned to a device by a network administrator, overriding the burned-in address. Locally administered addresses do not contain OUIs.
Universally administered and locally administered addresses are distinguished by setting the second least significant bit
Least significant bit
In computing, the least significant bit is the bit position in a binary integer giving the units value, that is, determining whether the number is even or odd. The lsb is sometimes referred to as the right-most bit, due to the convention in positional notation of writing less significant digits...
of the most significant byte 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 most significant byte 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. Consequently, this bit is 0 in all OUIs.
If the least significant bit of the most significant octet of an address is set to 0 (zero), the frame is meant to reach only one receiving NIC
Network card
A network interface controller is a computer hardware component that connects a computer to a computer network....
. This type of transmission is called unicast
Unicast
right|200pxIn computer networking, unicast transmission is the sending of messages to a single network destination identified by a unique address.-Addressing methodologies:...
. A unicast frame is transmitted to all nodes within the collision domain
Collision domain
A collision domain is a section of a network where data packets can collide with one another when being sent on a shared medium or through repeaters, in particular, when using early versions of Ethernet. A network collision occurs when more than one device attempts to send a packet on a network...
, which typically ends at the nearest network switch
Network switch
A network switch or switching hub is a computer networking device that connects network segments.The term commonly refers to a multi-port network bridge that processes and routes data at the data link layer of the OSI model...
or router. Only the node with the matching hardware MAC address will accept the frame; network frames with non-matching MAC-addresses are ignored, unless the device is in promiscuous mode
Promiscuous mode
In computer networking, promiscuous mode or promisc mode is a mode for a network interface controller that causes the NIC to pass all traffic it receives to the central processing unit rather than just passing frames the NIC is intended to receive...
.
If the least significant bit of the most significant address octet is set to 1, the frame will still be sent only once; however, NICs will choose to accept it based on different criteria than a matching MAC address: for example, based on a configurable list of accepted multicast MAC addresses. This is called multicast
Multicast
In computer networking, multicast is the delivery of a message or information to a group of destination computers simultaneously in a single transmission from the source creating copies automatically in other network elements, such as routers, only when the topology of the network requires...
addressing.
The following technologies use the MAC-48 identifier format:
- Ethernet
- 802.11IEEE 802.11IEEE 802.11 is a set of standards for implementing wireless local area network computer communication in the 2.4, 3.6 and 5 GHz frequency bands. They are created and maintained by the IEEE LAN/MAN Standards Committee . The base version of the standard IEEE 802.11-2007 has had subsequent...
wireless networks - BluetoothBluetoothBluetooth is a proprietary open wireless technology standard for exchanging data over short distances from fixed and mobile devices, creating personal area networks with high levels of security...
- IEEE 802.5 token ring
- most other IEEE 802 networks
- FDDI
- ATMAsynchronous Transfer ModeAsynchronous Transfer Mode is a standard switching technique designed to unify telecommunication and computer networks. It uses asynchronous time-division multiplexing, and it encodes data into small, fixed-sized cells. This differs from approaches such as the Internet Protocol or Ethernet that...
(switched virtual connections only, as part of an NSAP addressNSAP addressA Network Service Access Point address , defined in ISO/IEC 8348, is an identifying label for a Service Access Point used in OSI networking....
) - Fibre ChannelFibre ChannelFibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards , an American National Standards Institute –accredited standards...
and Serial Attached SCSISerial Attached SCSISerial Attached SCSI is a computer bus used to move data to and from computer storage devices such as hard drives and tape drives. SAS depends on a point-to-point serial protocol that replaces the parallel SCSI bus technology that first appeared in the mid 1980s in data centers and workstations,...
(as part of a World Wide NameWorld Wide NameA World Wide Name or World Wide Identifier is a unique identifier which identifies a particular Fibre Channel, Advanced Technology Attachment or Serial Attached SCSI target...
) - The ITU-TITU-TThe ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
G.hnG.hnG.hn is the common name for a home network technology family of standards developed under the International Telecommunication Union's Standardization arm and promoted by the HomeGrid Forum...
standard, which provides a way to create a high-speed (up to 1 gigabit/s) local area networkLocal area networkA local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...
using existing home wiring (power linesPower line communicationPower line communication or power line carrier , also known as power line digital subscriber line , mains communication, power line telecom , power line networking , or broadband over power lines are systems for carrying data on a conductor also used for electric power transmission.A wide range...
, phone lines and coaxial cablesEthernet over coaxEthernet over Coax is a family of technologies that supports the transmission of Ethernet frames over coaxial cable.- History :The first Ethernet standard, known as 10BASE5 in the family of IEEE 802.3, specified baseband operation over coaxial cable...
). The G.hn Application Protocol Convergence (APC) layer accepts Ethernet frames that use the MAC-48 format and encapsulates them into G.hn Medium Access Control Service Data Units (MSDUs).
The distinction between EUI-48 and MAC-48 identifiers is purely nominal: MAC-48 is used for network hardware; EUI-48 is used to identify other devices and software. (Thus, by definition, an EUI-48 is not in fact a "MAC address", although it is syntactically indistinguishable from one and assigned from the same numbering space.)
The IEEE now considers the label MAC-48 to be an obsolete term, previously used to refer to a specific type of EUI-48 identifier used to address hardware interfaces within existing 802-based networking applications, and thus not to be used in the future. Instead, the proprietary term EUI-48 should be used for this purpose.
EUI-64 identifiers are used in:
- FireWire
- IPv6IPv6Internet Protocol version 6 is a version of the Internet Protocol . It is designed to succeed the Internet Protocol version 4...
(Modified EUI-64 as the least-significant 64 bits of a unicast network address or link-local address when stateless autoconfiguration is used) - ZigBeeZigBeeZigBee is a specification for a suite of high level communication protocols using small, low-power digital radios based on an IEEE 802 standard for personal area networks. Applications include wireless light switches, electrical meters with in-home-displays, and other consumer and industrial...
/ 802.15.4IEEE 802.15IEEE 802.15 is a working group of the Institute of Electrical and Electronics Engineers IEEE 802 standards committee which specifies wireless personal area network standards. It includes seven task groups.-Task group 1 :...
/ 6LoWPAN6loWPAN6LoWPAN is an acronym of IPv6 over Low power Wireless Personal Area Networks. 6lowpan is the name of a working group in the internet area of the IETF....
wireless personal-area networks
The IEEE has built in several special address types to allow more than one network interface card to be addressed at one time:
- Packets sent to the broadcast addressBroadcast addressA broadcast address is a logical address at which all devices connected to a multiple-access communications network are enabled to receive datagrams...
, all one bits, are received by all stations on a local area network. In hexadecimalHexadecimalIn mathematics and computer science, hexadecimal is a positional numeral system with a radix, or base, of 16. It uses sixteen distinct symbols, most often the symbols 0–9 to represent values zero to nine, and A, B, C, D, E, F to represent values ten to fifteen...
the broadcast address would be FF:FF:FF:FF:FF:FF. A broadcast frame is floodedFlooding (computer networking)Flooding is a simple routing algorithm in which every incoming packet is sent through every outgoing link. See flooding algorithm for details.-Advantages:* If a packet can be delivered, it will ....
and is forwarded to and accepted by all other nodes. - Packets sent to a multicast addressMulticast addressA multicast address is a logical identifier for a group of hosts in a computer network, that are available to process datagrams or frames intended to be multicast for a designated network service...
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 802.5IBM token ringthumb|Two examples of token ring networks: a) Using a single [[Media Access Unit|MAU]] b) Using several MAUs connected to each otherthumb|Token ring networkthumb|IBM hermaphroditic connector with locking clipthumb|An IBM 8228 MAU...
.
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.
In addition, the EUI-64 numbering system encompasses both MAC-48 and EUI-48 identifiers by a simple translation mechanism. To convert a MAC-48 into an EUI-64, copy the OUI, append the two octets FF-FF and then copy the organization-specified extension identifier. To convert an EUI-48 into an EUI-64, the same process is used, but the sequence inserted is FF-FE. In both cases, the process can be trivially reversed when necessary. Organizations issuing EUI-64s are cautioned against issuing identifiers that could be confused with these forms. The IEEE policy is to discourage new uses of 48-bit identifiers in favor of the EUI-64 system.
IPv6
IPv6
Internet Protocol version 6 is a version of the Internet Protocol . It is designed to succeed the Internet Protocol version 4...
— one of the most prominent standards that uses a Modified EUI-64 — treats MAC-48 as EUI-48 instead (as it is chosen from the same address pool) and toggles the U/L bit (as this makes it easier to type locally assigned IPv6 addresses based on the Modified EUI-64). This results in extending MAC addresses (such as IEEE 802 MAC address) to Modified EUI-64 using only FF-FE (and never FF-FF) and with the U/L bit inverted.
Individual address block
An Individual Address BlockIndividual Address Block
The Individual Address Block is a block of identifiers that is formed by concatenating a 24-bit Organizationally Unique Identifier that is owned by the IEEE Registration Authority with an additional 12-bit extension identifier that is assigned by the IEEE Registration Authority and then reserving...
is a 24-bit OUI
Organizationally Unique Identifier
An Organizationally Unique Identifier is a 24-bit number that is purchased from the Institute of Electrical and Electronics Engineers, Incorporated Registration Authority...
managed by the IEEE Registration Authority, followed by 12 IEEE-provided bits (identifying the organization), and 12 bits for the owner to assign to individual devices. An IAB is ideal for organizations requiring fewer than 4097 unique 48-bit numbers (EUI-48).
Usage in Hosts
Although intended to be a permanent and globally unique identification, it is possible to change the MAC address on most modern hardware.Changing MAC addresses is necessary in network virtualization
Network virtualization
In computing, Network Virtualization is the process of combining hardware and software network resources and network functionality into a single, software-based administrative entity, a virtual network...
. It can also be used in the process of exploiting security vulnerabilities. This is called MAC spoofing
MAC spoofing
MAC spoofing is a technique for changing a factory-assigned Media Access Control address of a network interface on a networked device.- Motivation :...
.
A host cannot determine from the MAC address of another host whether that host is on the same link (network segment
Network segment
A network segment is a portion of a computer network. The nature and extent of a segment depends on the nature of the network and the device or devices used to interconnect end stations.-Ethernet:...
) as the sending host, or on a network segment bridged to that network segment.
In TCP/IP networks, the MAC address of an interface can be queried knowing the IP address
IP address
An Internet Protocol address is a numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing...
using the Address Resolution Protocol
Address Resolution Protocol
Address Resolution Protocol is a telecommunications protocol used for resolution of network layer addresses into link layer addresses, a critical function in multiple-access networks. ARP was defined by RFC 826 in 1982. It is Internet Standard STD 37...
(ARP) for Internet Protocol
Internet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
Version 4 (IPv4
IPv4
Internet Protocol version 4 is the fourth revision in the development of the Internet Protocol and the first version of the protocol to be widely deployed. Together with IPv6, it is at the core of standards-based internetworking methods of the Internet...
) or the Neighbor Discovery Protocol
Neighbor Discovery Protocol
The Neighbor Discovery Protocol is a protocol in the Internet Protocol Suite used with Internet Protocol Version 6 . It operates in the Link Layer of the Internet model and is responsible for address autoconfiguration of nodes, discovery of other nodes on the link, determining the Link Layer...
(NDP) for IPv6
IPv6
Internet Protocol version 6 is a version of the Internet Protocol . It is designed to succeed the Internet Protocol version 4...
. On broadcast networks, such as Ethernet, the MAC address uniquely identifies each node
Node (networking)
In communication networks, a node is a connection point, either a redistribution point or a communication endpoint . The definition of a node depends on the network and protocol layer referred to...
on that segment and allows frames to be marked for specific hosts. It thus forms the basis of most of the Link layer
Link Layer
In computer networking, the link layer is the lowest layer in the Internet Protocol Suite , the networking architecture of the Internet . It is the group of methods or protocols that only operate on a host's link...
(OSI Layer 2) networking upon which upper layer protocols rely to produce complex, functioning networks.
Usage in Switches
Layer 2 switches use MAC addresses to restrict packet transmission to the intended recipient.However, the effect is not immediate (address learning).
Many higher-end switches currently in distribution are Layer 3 switches. Such a switch supports IP multicast and therefore uses the IP address for routing. The switch preserves the MAC address for compatibility but does not need to use it for routing.
Bit-reversed notation
The standard notation, also called canonical format, for MAC addresses is written in transmission bit order with the least significant bit transmitted first, as seen in the output of the iproute2Iproute2
iproute2 is a collection of utilities for controllingTCP and UDP IP networking and traffic control in Linux, in both IPv4 and IPv6 networks. It is currently maintained by Stephen Hemminger...
/ifconfig
Ifconfig
ifconfig is a system administration utility in Unix-like operating systems to configure, control, and query TCP/IP network interface parameters from a command line interface or in system configuration scripts...
/ipconfig
Ipconfig
ipconfig in Microsoft Windows is a console application that displays all current TCP/IP network configuration values and can modify Dynamic Host Configuration Protocol DHCP and Domain Name System DNS settings....
command, for example.
However, since IEEE 802.3
IEEE 802.3
IEEE 802.3 is a working group and a collection of IEEE standards produced by the working group defining the physical layer and data link layer's media access control of wired Ethernet. This is generally a local area network technology with some wide area network applications...
(Ethernet) and IEEE 802.4 (Token Bus) send the bytes (octets) over the wire, left-to-right, with least significant bit in each byte first, while IEEE 802.5 (Token Ring) and IEEE 802.6
IEEE 802.6
IEEE 802.6 is a standard governed by the ANSI for Metropolitan Area Networks . It is an improvement of an older standard which used the Fiber distributed data interface network structure. The FDDI-based standard failed due to its expensive implementation and lack of compatibility with current LAN...
send the bytes over the wire with the most significant bit first, confusion may arise when an address in the latter scenario is represented with bits reversed from the canonical representation. For example, an address in canonical form
12-34-56-78-9A-BC would be transmitted over the wire as bits 01001000 00101100 01101010 00011110 01011001 00111101 in the standard transmission order (least significant bit first). But for Token Ring networks, it would be transmitted as bits 00010010 00110100 01010110 01111000 10011010 10111100 in most-significant-bit first order. The latter might be incorrectly displayed as 48-2C-6A-1E-59-3D. This is referred to as bit-reversed order, non-canonical form, MSB format, IBM format, or Token Ring format, as explained in RFC 2469. Canonical form is generally preferred, and used by all modern implementations.When the first switches supporting both Token Ring and Ethernet came out, some did not distinguish between canonical form and non-canonical form and so did not reverse MAC address bits as required. This led to cases of duplicate MAC addresses in the field.
See also
- Organizationally Unique IdentifierOrganizationally Unique IdentifierAn Organizationally Unique Identifier is a 24-bit number that is purchased from the Institute of Electrical and Electronics Engineers, Incorporated Registration Authority...
- Internet Protocol version 6IPv6Internet Protocol version 6 is a version of the Internet Protocol . It is designed to succeed the Internet Protocol version 4...
- Hot Standby Router ProtocolHot Standby Router ProtocolHot Standby Router Protocol is a Cisco proprietary redundancy protocol for establishing a fault-tolerant default gateway, and has been described in detail in RFC 2281....
or standard alternative VRRP Virtual Router Redundancy ProtocolVirtual Router Redundancy ProtocolThe Virtual Router Redundancy Protocol is a computer networking protocol that provides for automatic assignment of available Internet Protocol routers to participating hosts...
, which allows multiple routers to share one IP addressIP addressAn Internet Protocol address is a numerical label assigned to each device participating in a computer network that uses the Internet Protocol for communication. An IP address serves two principal functions: host or network interface identification and location addressing...
and MAC address to provide router redundancy. The OpenBSDOpenBSDOpenBSD is a Unix-like computer operating system descended from Berkeley Software Distribution , a Unix derivative developed at the University of California, Berkeley. It was forked from NetBSD by project leader Theo de Raadt in late 1995...
project has an open source alternative, the Common Address Redundancy Protocol (CARPCommon Address Redundancy ProtocolThe Common Address Redundancy Protocol or CARP is a protocol which allows multiple hosts on the same local network to share a set of IP addresses. Its primary purpose is to provide failover redundancy, especially when used with firewalls and routers. In some configurations CARP can also provide...
). On LinuxLinuxLinux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
, iptablesIptablesiptables is a user space application program that allows a system administrator to configure the tables provided by the Linux kernel firewall and the chains and rules it stores...
has a CLUSTERIP target. - NSAP addressNSAP addressA Network Service Access Point address , defined in ISO/IEC 8348, is an identifying label for a Service Access Point used in OSI networking....
, another endpoint addressing scheme. - Sleep Proxy ServiceSleep Proxy ServiceApple's Bonjour Sleep Proxy service is an open sourcecomponent of zero configuration networking, designed to assist in reducing power consumption of networked electronic devices. A device acting as a sleep proxy server will respond to Multicast DNS queries for another, compatible device which has...
, which may 'take over' another device's MAC address during certain periods
External links
- IEEE Registration Authority Tutorials
- IEEE Public OUI and Company_id Assignment lookup
- IEEE Public OUI list
- IEEE Public IAB list
- IANA Considerations and IETF Protocol Usage for IEEE 802 Parameters
- IANA list of Ethernet Numbers
- FermiLab: How to find your MAC address
- WiresharkWiresharkWireshark is a free and open-source packet analyzer. It is used for network troubleshooting, analysis, software and communications protocol development, and education...
's OUI Lookup Tool and MAC address list - MAC Find Vendor/Ethernet/Bluetooth MAC Address Lookup
- Michael Patton's "Ethernet Codes Master Page"
- 8086 Tools' MAC Address Lookup
- NetLookup Fast and easy lookup using MAC address or vendor
- MACVendorLookup.com Find by a list of addresses
- Hardware Address (finds items not found in the above)
- WLANController.com Blog MAC Address and Basic Service Set Identifier (BSSID) Geolocation