How To Find A Computer By Mac Address

Unique identifier assigned to network interfaces for communications on the concrete network segment

This article is about a type of network address. For the Apple computers, see Macintosh. For other similar terms, run into Mac.

Characterization of a UMTS router with MAC addresses for LAN and WLAN modules

A media access command address (MAC address) is a unique identifier assigned to a network interface controller (NIC) for utilise as a network address in communications inside a network segment. This use is common in most IEEE 802 networking technologies, including Ethernet, Wi-Fi, and Bluetooth. Within the Open Systems Interconnection (OSI) network model, MAC addresses are used in the medium access control protocol sublayer of the information link layer. As typically represented, MAC addresses are recognizable as vi groups of two hexadecimal digits, separated by hyphens, colons, or without a separator.

MAC addresses are primarily assigned past device manufacturers, and are therefore ofttimes referred to as the burned-in address, or every bit an Ethernet hardware address, hardware address, or physical address. Each address can be stored in hardware, such equally the card's read-only memory, or past a firmware mechanism. Many network interfaces, however, back up changing their MAC address. The address typically includes a manufacturer'southward organizationally unique identifier (OUI). MAC addresses are formed according to the principles of two numbering spaces based on Extended Unique Identifiers (EUI) managed by the Institute of Electric and Electronics Engineers (IEEE): EUI-48, which replaces the obsolete term MAC-48,^[1] and EUI-64.^[two]

Network nodes with multiple network interfaces, such equally routers and multilayer switches, must have a unique MAC address for each NIC in the same network. However, two NICs connected to two different networks tin can share the same MAC address.

Address details [edit]

The structure of a 48-scrap MAC address. The b0 fleck distinguishes multicast and unicast addressing and the b1 bit distinguishes universal and locally administered addressing.

The IEEE 802 MAC address originally comes from the Xerox Network Systems Ethernet addressing scheme.^[three] This 48-fleck accost space contains potentially ii⁴⁸ (over 281 trillion) possible MAC addresses. The IEEE manages allotment of MAC addresses, originally known equally MAC-48 and which it at present refers to as EUI-48 identifiers. The IEEE has a target lifetime of 100 years (until 2080) for applications using EUI-48 infinite and restricts applications appropriately. The IEEE encourages adoption of the more than plentiful EUI-64 for not-Ethernet applications.

The distinction betwixt EUI-48 and MAC-48 identifiers is in name and application only. MAC-48 was used to address hardware interfaces within existing 802-based networking applications; EUI-48 is at present used for 802-based networking and is also used to place other devices and software, for example Bluetooth.^{[ii] [4]} The IEEE at present considers MAC-48 to exist an obsolete term.^[1] EUI-48 is now used in all cases. In improver, the EUI-64 numbering system originally encompassed both MAC-48 and EUI-48 identifiers past a simple translation mechanism.^{[2] [a]} These translations have since been deprecated.^[two]

An Individual Accost Cake (IAB) is an inactive registry action which has been replaced by the MA-S (MA-S was previously named OUI-36 and have no overlaps in addresses with IAB^[5]) registry product as of January 1, 2014. The IAB uses an OUI from MA-50 (MAC accost cake large) registry was previously named OUI registry, the term OUI is still in use, but not for calling a registry^[v]) belonging to the IEEE Registration Authority, concatenated with 12 additional IEEE-provided $.25 (for a full of 36 bits), leaving only 12 bits for the IAB owner to assign to their (upwards to 4096) individual devices. An IAB is ideal for organizations requiring non more than 4096 unique 48-bit numbers (EUI-48). Unlike an OUI, which allows the assignee to assign values in various different number spaces (for example, EUI-48, EUI-64, and the diverse context-dependent identifier number spaces, like for SNAP or EDID (VSDB field)), the Individual Address Block could only be used to assign EUI-48 identifiers. All other potential uses based on the OUI from which the IABs are allocated are reserved and remain the belongings of the IEEE Registration Authority. Between 2007 and September 2012, the OUI value 00:l:C2 was used for IAB assignments. Later September 2012, the value 40:D8:55 was used. The owners of an already assigned IAB may go on to use the consignment.^[six]

MA-S (MAC address block modest) registry activity includes both a 36-bit unique number used in some standards and the assignment of a block of EUI-48 and EUI-64 identifiers (while owner of IAB cannot assign EUI-64) by the IEEE Registration Authority. MA-S does non include consignment of an OUI.

There is also some other registry which is called MA-M (MAC accost block medium). The MA-M consignment cake provides both ii^xx EUI-48 identifiers and 2³⁶ EUI-64 identifiers (that means first 28 bits are IEEE assigned $.25). The first 24 bits of the assigned MA-M cake are an OUI assigned to IEEE that will non be reassigned, and so the MA-M does not include assignment of an OUI.

Universal vs. local (U/L flake) [edit]

Addresses tin either be universally administered addresses (UAA) or locally administered addresses (LAA). A universally administered accost is uniquely assigned to a device by its manufacturer. The offset three octets (in transmission order) identify the system that issued the identifier and are known equally the organizationally unique identifier (OUI).^[2] The remainder of the accost (3 octets for EUI-48 or 5 for EUI-64) are assigned by that organisation in well-nigh any manner they please, discipline to the constraint of uniqueness. A locally administered address is assigned to a device past software or a network ambassador, overriding the burned-in address for physical devices.

Locally administered addresses are distinguished from universally administered addresses by setting (assigning the value of one to) the second-to the lowest degree-meaning scrap of the showtime octet of the address. This bit is also referred to as the U/Fifty bit, short for Universal/Local, which identifies how the address is administered.^{[vii] [viii]} If the bit is 0, the accost is universally administered, which is why this bit is 0 in all UAAs. If it is 1, the address is locally administered. In the case address 06-00-00-00-00-00 the outset octet is 06 (hexadecimal), the binary class of which is 000001ane0, where the second-least-significant bit is 1. Therefore, it is a locally administered address.^[nine] Even though many hypervisors manage dynamic MAC addresses inside their own OUI, often it is useful to create an entire unique MAC within the LAA range.^[10]

Universal addresses that are administered locally [edit]

In virtualisation, hypervisors such as QEMU and Xen have their own OUIs. Each new virtual machine is started with a MAC address fix by assigning the final three bytes to exist unique on the local network. While this is local administration of MAC addresses, it is non an LAA in the IEEE sense.

An historical case of this hybrid situation is the DECnet protocol, where the universal MAC accost (OUI AA-00-04, Digital Equipment Corporation) is administered locally. The DECnet software assigns the concluding 3 bytes for the complete MAC address to exist AA-00-04-00-XX-YY where 20-YY reflects the DECnet network address xx.yy of the host. This eliminates the need for DECnet to accept an address resolution protocol since the MAC address for whatever DECnet host can be determined from its DECnet address.

Unicast vs. multicast (I/G bit) [edit]

The least significant bit of an address'southward commencement octet is referred to as the I/G, or Private/Group, bit.^{[7] [8]} When this scrap is 0 (nada), the frame is meant to accomplish but one receiving NIC.^[xi] This blazon of transmission is called unicast. A unicast frame is transmitted to all nodes within the collision domain. In a modern wired setting the collision domain usually is the length of the Ethernet cable between two network cards. In a wireless setting, the collision domain is all receivers that can detect a given wireless signal. If a switch does not know which port leads to a given MAC address, the switch will forrad a unicast frame to all of its ports (except the originating port), an action known as unicast flood.^[12] 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 style.

If the least significant flake of the first octet is set to 1 (i.e. the second hexadecimal digit is odd) the frame will withal exist sent simply once; however, NICs volition choose to have it based on criteria other than the matching of a MAC address: for instance, based on a configurable list of accepted multicast MAC addresses. This is chosen multicast addressing.

The IEEE has built in several special address types to permit more than 1 network interface menu to be addressed at in one case:

• Packets sent to the broadcast address, all ane $.25, are received by all stations on a local area network. In hexadecimal the broadcast address would be FF:FF:FF:FF:FF:FF . A circulate frame is flooded and is forwarded to and accustomed 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 accost.
• Functional addresses identify 1 or more Token Ring NICs that provide a item service, defined in IEEE 802.5.

These are all examples of group addresses, as opposed to private addresses; the least significant fleck of the beginning 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.

Ranges of group and locally administered addresses [edit]

The U/50 and I/G bits are handled independently, and there are instances of all four possibilities.^[9] IPv6 multicast uses locally administered, multicast MAC addresses in the range 33‑33‑xx‑twenty‑20‑20 (with both bits set).^[13]

Given the locations of the U/50 and I/Yard bits, they tin be discerned in a single digit in common MAC address notation as shown in the following table:

Universal/Local and Individual/Group bits in MAC addresses

U/L I/G	Universally administered	Locally administered
Unicast (individual)	x0‑xx‑20‑xx‑xx‑xx x4‑twenty‑xx‑20‑xx‑xx x8‑xx‑twenty‑xx‑xx‑twenty xC‑twenty‑20‑xx‑xx‑xx	x2‑xx‑20‑xx‑xx‑xx x6‑xx‑20‑xx‑twenty‑xx xA‑xx‑xx‑twenty‑20‑twenty xDue east‑xx‑twenty‑twenty‑xx‑xx
Multicast (group)	x1‑xx‑twenty‑xx‑xx‑xx 10v‑xx‑xx‑20‑20‑xx xnine‑xx‑20‑20‑xx‑twenty xD‑xx‑twenty‑xx‑xx‑20	x3‑20‑twenty‑xx‑20‑xx x7‑xx‑xx‑xx‑xx‑xx tenB‑20‑20‑xx‑xx‑xx xF‑twenty‑xx‑xx‑xx‑xx

Applications [edit]

The following network technologies use the EUI-48 identifier format:

• IEEE 802 networks
  • Ethernet
  • 802.11 wireless networks (Wi-Fi)
  • Bluetooth
  • IEEE 802.5 Token Ring
• Cobweb Distributed Data Interface (FDDI)
• Asynchronous Transfer Manner (ATM), switched virtual connections only, as part of an NSAP address
• Fibre Channel and Serial Attached SCSI (as part of a World Broad Name)
• The ITU-T Thousand.hn standard, which provides a fashion to create a high-speed (up to 1 gigabit/southward) local expanse network using existing home wiring (power lines, telephone lines and coaxial cables). The Yard.hn Awarding Protocol Convergence (APC) layer accepts Ethernet frames that use the EUI-48 format and encapsulates them into G.hn Medium Access Command Service Data Units (MSDUs).

Every device that connects to an IEEE 802 network (such equally Ethernet and Wi-Fi) has an EUI-48 address. Common networked consumer devices such as PCs, smartphones and tablet computers apply EUI-48 addresses.

EUI-64 identifiers are used in:

• IEEE 1394 (FireWire)
• InfiniBand
• IPv6 (Modified EUI-64 equally the least-meaning 64 bits of a unicast network address or link-local address when stateless address autoconfiguration is used.)^[14] IPv6 uses a modified EUI-64, treats MAC-48 as EUI-48 instead (as it is chosen from the aforementioned accost pool) and inverts the local bit.^[b] This results in extending MAC addresses (such as IEEE 802 MAC address) to modified EUI-64 using only FF-Atomic number 26 (and never FF-FF ) and with the local bit inverted.^[fifteen]
• ZigBee / 802.15.four / 6LoWPAN wireless personal-expanse networks
• IEEE 11073-20601 (IEEE 11073-20601 compliant medical devices)^[xvi]

Usage in hosts [edit]

On broadcast networks, such as Ethernet, the MAC accost is expected to uniquely identify each node on that segment and allows frames to be marked for specific hosts. Information technology 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.

Many network interfaces support changing their MAC accost. On near Unix-like systems, the command utility ifconfig may exist used to remove and add link address aliases. For instance, the active ifconfig directive may be used on NetBSD to specify which of the fastened addresses to actuate.^[17] Hence, diverse configuration scripts and utilities allow the randomization of the MAC accost at the fourth dimension of booting or before establishing a network connection.

Changing MAC addresses is necessary in network virtualization. In MAC spoofing, this is practiced in exploiting security vulnerabilities of a computer system. Some modernistic operating systems, such as Apple iOS and Android, especially in mobile devices, are designed to randomize the assignment of a MAC address to network interface when scanning for wireless access points to avoid tracking systems.^{[18] [19]}

In Internet Protocol (IP) networks, the MAC accost of an interface corresponding to an IP accost may be queried with the Address Resolution Protocol (ARP) for IPv4 and the Neighbor Discovery Protocol (NDP) for IPv6, relating OSI Layer 3 addresses to Layer 2 addresses.

Tracking [edit]

Randomization [edit]

According to Edward Snowden, the The states National Security Agency has a system that tracks the movements of mobile devices in a metropolis past monitoring MAC addresses.^[xx] To avert this practice, Apple has started using random MAC addresses in iOS devices while scanning for networks.^[eighteen] Other vendors followed quickly. MAC address randomization during scanning was added in Android starting from version 6.0,^[19] Windows 10,^[21] and Linux kernel 3.18.^[22] The actual implementations of the MAC accost randomization technique vary largely in different devices.^[23] Moreover, diverse flaws and shortcomings in these implementations may allow an assailant to rails a device even if its MAC address is changed, for case its probe requests' other elements,^{[24] [25]} or their timing.^{[26] [23]} If random MAC addresses are non used, researchers have confirmed that it is possible to link a existent identity to a particular wireless MAC address.^{[27] [28]}

Other data leakage [edit]

Using wireless access points in SSID-hidden way (network cloaking), a mobile wireless device may not but disclose its own MAC address when traveling, but even the MAC addresses associated to SSIDs the device has already continued to, if they are configured to transport these as part of probe request packets. Alternative modes to prevent this include configuring access points to exist either in beacon-dissemination mode or probe-response with SSID mode. In these modes, probe requests may exist unnecessary or sent in broadcast manner without disclosing the identity of previously known networks.^[29]

Anonymization [edit]

Notational conventions [edit]

The standard (IEEE 802) format for printing EUI-48 addresses in human-friendly class is six groups of two hexadecimal digits, separated by hyphens ( - ) in transmission order (e.thousand. 01-23-45-67-89-AB ). This grade is too commonly used for EUI-64 (e.1000. 01-23-45-67-89-AB-CD-EF ).^[two] Other conventions include six groups of two hexadecimal digits separated by colons (:) (eastward.g. 01:23:45:67:89:AB ), and three groups of iv hexadecimal digits separated past dots (.) (e.g. 0123.4567.89AB ); again in transmission order.^[30]

Chip-reversed notation [edit]

The standard notation, likewise called approved format, for MAC addresses is written in transmission order with the least pregnant fleck of each byte transmitted first, and is used in the output of the ifconfig, ip address, and ipconfig commands, for example.

Nonetheless, since IEEE 802.iii (Ethernet) and IEEE 802.4 (Token Bus) ship the bytes (octets) over the wire, left-to-right, with the to the lowest degree meaning bit in each byte first, while IEEE 802.5 (Token Band) and IEEE 802.6 (FDDI) send the bytes over the wire with the about significant bit first, confusion may arise when an address in the latter scenario is represented with $.25 reversed from the canonical representation. For example, an address in canonical form 12-34-56-78-9A-BC would be transmitted over the wire equally bits 01001000 00101100 01101010 00011110 01011001 00111101 in the standard transmission lodge (least significant flake first). Simply for Token Ring networks, it would be transmitted equally bits 00010010 00110100 01010110 01111000 10011010 10111100 in most-significant-bit first order. The latter might be incorrectly displayed every bit 48-2C-6A-1E-59-3D . This is referred to as bit-reversed order, not-canonical form, MSB format, IBM format, or Token Ring format, equally explained in RFC 2469.

Run into too [edit]

• Hot Standby Router Protocol
• MAC filtering
• Network direction
• Slumber Proxy Service, which may spoof another device'southward MAC accost during certain periods
• Transparent bridging
• Virtual Router Redundancy Protocol

Notes [edit]

1. ^ To convert a MAC-48 into an EUI-64, re-create the OUI, suspend the two octets FF-FF and so copy the organization-specified extension identifier. To catechumen an EUI-48 into an EUI-64, the aforementioned procedure is used, simply the sequence inserted is FF-Iron .^[2] In both cases, the process could be trivially reversed when necessary. Organizations issuing EUI-64s were cautioned against issuing identifiers that could be confused with these forms.
2. ^ With local identifiers indicated with a zero bit, locally assigned EUI-64 begin with leading zeroes and it is easier for administrators to type locally assigned IPv6 addresses based on the modified EUI-64

References [edit]

1. ^ ^{a b} "MAC Address Block Small (MA-S)". Retrieved 2019-02-24 .
2. ^ ^{a b c d e f g} "Guidelines for Utilize of Extended Unique Identifier (EUI), Organizationally Unique Identifier (OUI), and Company ID (CID)" (PDF). IEEE Standards Association. IEEE. Retrieved five August 2018.
3. ^ IEEE Std 802-2001 (PDF). The Plant of Electrical and Electronics Engineers, Inc. (IEEE). 2002-02-07. p. 19. ISBN978-0-7381-2941-9 . Retrieved 2011-09-08 . The universal administration of LAN MAC addresses began with the Xerox Corporation administering Cake Identifiers (Block IDs) for Ethernet addresses.
4. ^ "IEEE-SA - IEEE Registration Authority". standards.ieee.org . Retrieved 2018-09-xx .
5. ^ ^{a b} "IEEE-SA - IEEE Registration Authority". standards.ieee.org . Retrieved 2018-11-27 .
6. ^ "IEEE-SA - IEEE Registration Potency". standards.ieee.org . Retrieved 2018-09-20 .
7. ^ ^{a b} "Ethernet frame IG/LG bit explanation - Wireshark". networkengineering.stackexchange.com . Retrieved 2021-01-05 .
8. ^ ^{a b} "RFC 4291 IP Version 6 Addressing Architecture Appendix A". tools.ietf.org . Retrieved 2021-01-05 .
9. ^ ^{a b} "Standard Group MAC Addresses: A Tutorial Guide" (PDF). IEEE-SA. Retrieved 2018-09-xx .
10. ^ "Generating a New Unique MAC Address". RedHat. Retrieved 2020-06-15 .
11. ^ "Guidelines for Fibre Channel Apply of the Organizationally Unique Identifier (OUI)" (PDF). IEEE-SA. Retrieved 2018-10-11 .
12. ^ "Overview of Layer 2 Switched Networks and Communication | Getting Started with LANs | Cisco Support Community | 5896 | 68421". supportforums.cisco.com. 2011-07-23. Retrieved 2016-05-17 .
13. ^ RFC 7042 ii.three.1.
14. ^ S. Thomson; T. Narten; T. Jinmei (September 2007). IPv6 Stateless Address Autoconfiguration. Network Working Group, IETF. doi:10.17487/RFC4862. RFC 4862.
15. ^ IANA Considerations and IETF Protocol Usage for IEEE 802 Parameters. IETF. September 2008. sec. 2.2.ane. doi:x.17487/RFC7042. RFC 7042.
16. ^ IEEE P11073-20601 Health information science—Personal wellness device advice Office 20601: Application profile—Optimized Exchange Protocol
17. ^ "ifconfig(eight) manual page". Retrieved xvi October 2016.
18. ^ ^{a b} Mamiit, Aaron (2014-06-12). "Apple Implements Random MAC Address on iOS viii. Goodbye, Marketers". Tech Times . Retrieved 2014-12-01 .
19. ^ ^{a b} "Android vi.0 Changes". Android developers . Retrieved 2018-08-22 .
20. ^ Bamford, James (2014-08-13). "The About Wanted Man in the Globe". Wired: 4. Retrieved 2014-12-01 .
21. ^ Winkey Wang. "Wireless networking in Windows 10".
22. ^ Emmanuel Grumbach. "iwlwifi: mvm: support random MAC address for scanning". Linux commit effd05ac479b . Retrieved 2018-08-22 .
23. ^ ^{a b} Célestin Matte (December 2017). Wi-Fi Tracking: Fingerprinting Attacks and Counter-Measures. 2017 (Theses). Université de Lyon. Retrieved 2018-08-22 .
24. ^ Vanhoef Mathy and Matte Célestin and Cunche Mathieu and Cardoso Leonardo and Piessens Frank (2016-05-thirty). "Why MAC address randomization is not enough: An analysis of Wi-Fi network discovery mechanisms". Retrieved 2018-08-22 .
25. ^ Martin Jeremy and Mayberry Travis and Donahue Collin and Foppe Lucas and Brown Lamont and Riggins Chadwick and Rye Erik C and Brown Dane. "A study of MAC address randomization in mobile devices and when it fails" (PDF). 2017 . Retrieved 2018-08-22 .
26. ^ Matte Célestin and Cunche Mathieu and Rousseau Franck and Vanhoef Mathy (2016-07-18). "Defeating MAC address randomization through timing attacks". Retrieved 2018-08-22 .
27. ^ Cunche, Mathieu. "I know your MAC Address: Targeted tracking of individual using Wi-Fi" (PDF). 2013 . Retrieved nineteen Dec 2014.
28. ^ Muhammad Hassan. "How to Detect iPhone MAC Address".
29. ^ "Hidden network no beacons". security.stackexchange.com . Retrieved 16 October 2016.
30. ^ "Agentless Host Configuration Scenario". Configuration Guide for Cisco Secure ACS 4.ii. Cisco. February 2008. Archived from the original on 2016-08-02. Retrieved 2015-09-xix . You can enter the MAC address in the following formats for representing MAC-48 addresses in human-readable form: six groups of two hexadecimal digits, separated by hyphens (-) in transmission order,[...]six groups of two separated past colons (:),[...]three groups of iv hexadecimal digits separated by dots (.)...

External links [edit]

• IEEE Registration Authority Tutorials
• IEEE Registration Authority - Frequently Asked Questions
• IEEE Public OUI and Company ID, etc. Assignment lookup
• IEEE Public OUI/MA-L list
• IEEE Public OUI-28/MA-M list
• IEEE Public OUI-36/MA-South list
• IEEE Public IAB list
• IEEE IAB and OUI MAC Address Lookup Database and API
• RFC 7042. IANA Considerations and IETF Protocol and Documentation Usage for IEEE 802 Parameters
• IANA list of Ethernet Numbers
• Wireshark'due south OUI Lookup Tool and MAC accost list

Source: https://en.wikipedia.org/wiki/MAC_address

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