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In computer networking a Media Access Control address (MAC address) or Ethernet Hardware Address (EHA) or hardware address or adapter address is a quasi-unique identifier attached to most network adapters (NIC or Network Interface Card). A computer network is a group of interconnected Computers. Networks may be classified according to a wide variety of characteristics The Media Access Control (MAC Data communication protocol sub-layer also known as the Medium Access Control is a sublayer of the Data Link Layer specified in the With reference to a given (possibly implicit set of objects a unique identifier is any Identifier which is guaranteed to be unique among all identifiers used for those objects A Network card, Network Adapter, LAN Adapter or NIC (network interface card is a piece of Computer hardware designed to allow computers It is a number that serves as an identifier for a particular network adapter. Thus network cards (or built-in network adapters) in two different computers will have different MAC addresses, as would an Ethernet adapter and a wireless adapter in the same computer, and as would multiple network cards in a router. Ethernet is a family of frame -based Computer networking technologies for Local area networks (LANs However, it is possible to change the MAC address on most of today's hardware, often referred to as MAC spoofing.

Most layer 2 network protocols use one of three numbering spaces managed by the Institute of Electrical and Electronics Engineers (IEEE): MAC-48, EUI-48, and EUI-64, which are designed to be globally unique. The Data Link Layer is Layer 2 of the seven-layer OSI model. It responds to service requests from the Network Layer and issues service requests to the In computing, a protocol is a convention or standard that controls or enables the connection Communication, and Data transfer between two computing The Institute of Electrical and Electronics Engineers or IEEE (read eye-triple-e) is an international Non-profit, professional organization Not all communications protocols use MAC addresses, and not all protocols require globally unique identifiers. The IEEE claims trademarks on the names "EUI-48" and "EUI-64" ("EUI" stands for Extended Unique Identifier). A trademark or trade mark, represented by the symbols ™ and ®, or mark is a distinctive sign or indicator used by an individual

MAC addresses, unlike IP addresses and IPX addresses, are not divided into "host" and "network" portions. An Internet Protocol ( IP) address is a numerical identification ( Logical address) that is assigned to devices participating in a Computer network Internetwork Packet Exchange ( IPX) is the OSI-model Network layer protocol in the IPX/SPX Protocol stack. Therefore, a host cannot determine from the MAC address of another host whether that host is on the same layer 2 network segment as the sending host or a network segment bridged to that network segment. A network segment is a portion of a Computer network wherein every device communicates using the same Physical layer. A network bridge connects multiple Network segments at the Data link layer (layer 2 of the OSI model, and the term layer 2 switch is often

ARP is commonly used to convert from addresses in a layer 3 protocol such as Internet Protocol (IP) to the layer 2 MAC address. In Computer networking the Address Resolution Protocol ( ARP) is the method for finding a host's hardware address when only its Network Layer address is The Network Layer is Layer 3 (of seven in the OSI model of networking The Internet Protocol ( IP) is a protocol used for communicating data across a Packet-switched Internetwork using the Internet Protocol The Data Link Layer is Layer 2 of the seven-layer OSI model. It responds to service requests from the Network Layer and issues service requests to the On broadcast networks, such as Ethernet, the MAC address allows each host to be uniquely identified and allows frames to be marked for specific hosts. It thus forms the basis of most of the layer 2 networking upon which higher OSI Layer protocols are built to produce complex, functioning networks. The Open Systems Interconnection Basic Reference Model (OSI Reference Model or OSI Model) is an abstract description for layered communications and computer Network protocol

Contents

Notational conventions

The standard (IEEE 802) format for printing MAC-48 addresses in human-readable media is six groups of two hexadecimal digits, separated by hyphens (-) in transmission order, e. g. 01-23-45-67-89-ab. This form is also commonly used for EUI-64. Other conventions include six groups of two separated by colons (:), e. g. 01:23:45:67:89:ab; or three groups of four hexadecimal digits separated by dots (. In Mathematics and Computer science, hexadecimal (also base -, hexa, or hex) is a Numeral system with a ), e. g. 0123. 4567. 89ab; again in transmission order.

Address details

The original IEEE 802 MAC address comes from the original Xerox Ethernet addressing scheme. 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 Xerox Corporation ( (name ˈziːrɒks is a global document management company which manufactures and sells a range of color and black-and-white printers, multifunction [1] 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" (BIA). The first three octets (in transmission order) identify the organization that issued the identifier and are known as the Organizationally Unique Identifier (OUI). In Computing, an octet is a grouping of eight Bits Octet, with the only exception noted below always refers to an entity having exactly eight An Organizationally Unique Identifier ( OUI) is a 24-bit number that is purchased from the Institute of Electrical and Electronics Engineers Incorporated (IEEE 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. In Computing, the least significant bit ( lsb) is the Bit position in a binary Integer giving the units value that is determining If the bit is 0, the address is universally administered. If it is 1, the address is locally administered. The bit is 0 in all OUIs. For example, 02-00-00-00-00-01. The most significant byte is 02h. The binary is 00000010 and the second least significant bit is 1. Therefore, it is a locally administered address. [2]

If the least significant bit of the most significant byte is set to a 0, the packet is meant to reach only one receiving NIC. A Network card, Network Adapter, LAN Adapter or NIC (network interface card is a piece of Computer hardware designed to allow computers This is called unicast. In Computer networking unicast transmission is the sending of information packets to a single destination If the least significant bit of the most significant byte is set to a 1, the packet is meant to be sent only once but still reach several NICs. This is called multicast. Multicast is a network addressing method for the delivery of Information to a group of destinations simultaneously using the most efficient strategy

MAC-48 and EUI-48 addresses are usually shown in hexadecimal format, with each octet separated by a dash or colon. In Mathematics and Computer science, hexadecimal (also base -, hexa, or hex) is a Numeral system with a An example of a MAC-48 address would be "00-08-74-4C-7F-1D". If you cross-reference the first three octets with IEEE's OUI assignments,[3] you can see that this MAC address came from Dell Computer Corp. The Institute of Electrical and Electronics Engineers or IEEE (read eye-triple-e) is an international Non-profit, professional organization The multinational technology company Dell Inc develops manufactures sells and supports Personal computers and other computer-related products The last three octets represent the serial number assigned to the adapter by the manufacturer.

The following technologies use the MAC-48 identifier format:

The distinction between EUI-48 and MAC-48 identifiers is purely semantic: MAC-48 is used for network hardware; EUI-48 is used to identify other devices and software. Token ring Local area network (LAN technology is a local area network protocol which resides at the Data link layer Fiber distributed data interface ( FDDI) provides a standard for Data transmission in a Local area network In electronic digital data transmission systems the Network protocol Asynchronous Transfer Mode (ATM encodes data traffic into small fixed-sized cells Network Service Access Point ( NSAP) addresses defined in ISO/IEC 8348 are identifying labels for network endpoints used in OSI networking Fibre Channel, or FC, is a Gigabit -speed network technology primarily used for Storage networking. Introduction A typical Serial Attached SCSI system consists of the following basic components An Initiator is a device that originates device service A World Wide Name (WWN or World Wide Identifier (WWID is a unique identifier in a Fibre Channel or Serial Attached SCSI storage network. (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 which was previously used to refer to a specific type of EUI-48 identifier used to address hardware interfaces within existing 802-based networking applications and should not be used in the future. Instead, the 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 "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 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 part. 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 EUI-64—treats MAC-48 as EUI-48 instead (as it's chosen from the same address pool). Internet Protocol version 6 ( IPv6) is an Internet Layer protocol for packet -switched internetworks. This results in extending MAC addresses (such as IEEE 802 MAC address) to EUI-64 using "FF-FE" rather than "FF-FF. "

Individual address block

An Individual Address Block comprises 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. The Individual Address Block (IAB is a block of identifiers that is formed by concatenating a 24-bit Organizationally Unique Identifier (OUI that is owned by An Organizationally Unique Identifier ( OUI) is a 24-bit number that is purchased from the Institute of Electrical and Electronics Engineers Incorporated (IEEE An IAB is ideal for organizations requiring fewer than 4097 unique 48-bit numbers (EUI-48). [4]

Bit-reversed notation

The standard transmission order notation for MAC addresses, as seen in the output of the ifconfig command for example, is also called canonical format. The Unix command ifconfig serves to configure and control TCP/IP Network interfaces from a Command line interface (CLI

However, since IEEE 802.3 (Ethernet) and IEEE 802.4 (Token Bus) send the bits over the wire with least significant bit first, while IEEE 802.5 (Token Ring) and IEEE 802.6 send the bits over the wire with most significant bit first, confusion may arise where an address in the latter scenario is represented with bits reversed from the canonical representation. IEEE 8023 is a collection of IEEE standards defining the Physical layer, and the media access control (MAC sublayer of the Data link layer, IEEE 8024 defines the Medium access control (MAC layer for Bus networks that use a Token-passing mechanism ( Token bus networks Token ring Local area network (LAN technology is a local area network protocol which resides at the Data link layer IEEE 8026 is a standard governed by the ANSI for Metropolitan Area Networks (MAN So for instance, an address whose canonical form is 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. If care is not taken to translate correctly and consistently to the canonical representation, the latter might be displayed as 482C6A1E593D, which could cause confusion. This would be referred to as "Bit-reversed order", "Non-canonical form", "MSB format", "IBM format", or "Token Ring format" as explained by RFC 2469. Canonical form is preferred.

See also

References

  1. ^ IEEE Std 802®-2001
  2. ^ Standard Group MAC Addresses: A Tutorial Guide
  3. ^ IEEE OUI and Company_id Assignments
  4. ^ What is an Individual Address Block?. Retrieved on 2006-07-09. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 455 - Roman military commander Avitus is proclaimed Emperor of the Western Roman Empire.

External links

Dictionary

MAC address

-noun

  1. (computing, networking) Media Access Control address. An OSI device layer address used by Ethernet, 802.11 wireless, Bluetooth, FDDI, ATM, and Fiber Channel networking technologies, all of which share the same address space, consisting of a globally unique number assigned to each network jack, wireless network radio, or other sort of network interface.
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