In IEEE 802.11 wireless local area networking standards (including Wi‑Fi ), a service set is a group of wireless network devices which share a service set identifier ( SSID )—typically the natural language label that users see as a network name. (For example, all of the devices that together form and use a Wi‑Fi network called "Foo" are a service set.) A service set forms a logical network of nodes operating with shared link-layer networking parameters; they form one logical network segment.
48-444: A service set is either a basic service set ( BSS ) or an extended service set ( ESS ). A basic service set is a subgroup, within a service set, of devices that share physical-layer medium access characteristics (e.g. radio frequency, modulation scheme, security settings) such that they are wirelessly networked. The basic service set is defined by a basic service set identifier ( BSSID ) shared by all devices within it. The BSSID
96-481: A flag to express that the SSID is UTF-8 -encoded and could contain any Unicode text. Wireless network stacks must still be prepared to handle all possible values in the SSID field. Since the contents of an SSID field are arbitrary, the 802.11 standard permits devices to advertise the presence of a wireless network with beacon packets in which the SSID field is set to null. A null SSID (the SSID element's length field
144-784: A particular wireless MAC address. Randomized MAC addresses can be identified by the "locally administered" bit described above. Using wireless access points in SSID -hidden mode ( network cloaking ), a mobile wireless device may not only disclose its own MAC address when traveling, but even the MAC addresses associated to SSIDs the device has already connected to, if they are configured to send these as part of probe request packets. Alternative modes to prevent this include configuring access points to be either in beacon-broadcasting mode or probe-response with SSID mode. In these modes, probe requests may be unnecessary or sent in broadcast mode without disclosing
192-639: A service set. Normally it is broadcast in the clear by stations in beacon packets to announce the presence of a network and seen by users as a wireless network name. Unlike basic service set identifiers, SSIDs are usually customizable. These SSIDs can be zero to 32 octets long, and are, for convenience, usually in a natural language , such as English. The 802.11 standards prior to the 2012 edition did not define any particular encoding or representation for SSIDs, which were expected to be treated and handled as an arbitrary sequence of 0–32 octets that are not limited to printable characters . IEEE Std 802.11-2012 defines
240-412: A single network to the logical link control layer by using the same SSID. Thus, from the perspective of the logical link control layer, stations within an ESS may communicate with one another, and mobile stations may move transparently from one participating basic service set to another (within the same ESS). Extended service sets make possible distribution services such as centralized authentication. From
288-616: A system, the BSS created by the access point is distinct from the mesh network, and a wireless client of that BSS is not part of the MBSS. The formation of the mesh BSS, as well as wireless traffic management (including path selection and forwarding) is negotiated between the nodes of the mesh infrastructure. The mesh BSS is distinct from the networks (which may also be wireless) used by a mesh's redistribution points to communicate with one another. The service set identifier ( SSID ) defines or extends
336-405: A target lifetime of 100 years (until 2080) for applications using EUI-48 space and restricts applications accordingly. The IEEE encourages adoption of the more plentiful EUI-64 for non-Ethernet applications. The distinctions between EUI-48 and MAC-48 identifiers are in name and application only. MAC-48 was used to address hardware interfaces within existing 802-based networking applications; EUI-48
384-425: A value of all 1s is used to indicate the wildcard BSSID, usable only during probe requests or for communications that take place outside the context of a BSS. An independent BSS ( IBSS ), or ad hoc network , is created by peer devices among themselves without network infrastructure. A temporary network created by a cellular telephone to share its Internet access with other devices is a common example. In contrast to
432-455: Is 0 (zero), the frame is meant to reach only one receiving network interface . 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 switches , not simple hubs ) the collision domain usually is the length of the Ethernet cabling between two network interfaces. In a wireless setting,
480-483: Is a unique identifier assigned to a network interface controller (NIC) for use as a network address in communications within 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
528-440: Is a 48-bit label that conforms to MAC-48 conventions. While a device may have multiple BSSIDs, usually each BSSID is associated with at most one basic service set at a time. A basic service set should not be confused with the coverage area of an access point, known as the basic service area ( BSA ). An infrastructure BSS is created by an infrastructure device called an access point ( AP ) for other devices to join. (Note that
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#1732772247029576-426: Is a wireless network, created by multiple access points, which appears to users as a single, seamless network, such as a network covering a home or office that is too large for reliable coverage by a single access point. It is a set of one or more infrastructure basic service sets on a common logical network segment (i.e. same IP subnet and VLAN). Key to the concept is that the participating basic service sets appear as
624-443: Is always set to 0 (individual), the universal/local bit of the address is always set to 1 (local), and the remaining 46 bits are randomly generated. A mesh basic service set ( MBSS ) is a self-contained network of mesh stations that share a mesh profile , defined in 802.11s . Each node may also be an access point hosting its own basic service set, for example using the mesh BSS to provide Internet access for local users. In such
672-698: Is an inactive registry which has been replaced by the MA-S ( MAC address block, small ), previously named OUI-36 , and has no overlaps in addresses with the IAB registry product as of January 1, 2014. The IAB uses an OUI from the MA-L ( MAC address block, large ) registry, previously called the OUI registry. The term OUI is still in use, but the IEEE Registration Authority does not administer them. An OUI
720-722: Is called multicast addressing. 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. The U/L and I/G bits are handled independently, and there are instances of all four possibilities. IPv6 multicast uses locally administered, multicast MAC addresses in
768-408: Is concatenated with 12 additional IEEE-provided bits (for a total of 36 bits), leaving only 12 bits for the organisation owning the IAB to assign to its (up to 4096) individual devices. An IAB is ideal for organizations requiring not 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
816-489: Is now used for 802-based networking and is also used to identify other devices and software, for example Bluetooth . The IEEE now considers MAC-48 to be an obsolete term. EUI-48 is now used in all cases. In addition, the EUI-64 numbering system originally encompassed both MAC-48 and EUI-48 identifiers by a simple translation mechanism. These translations have since been deprecated. The Individual Address Block (IAB)
864-561: Is optional. The following network technologies use the EUI-48 identifier format: Every device that connects to an IEEE 802 network (such as Ethernet and Wi-Fi) has an EUI-48 address. Common networked consumer devices such as PCs, smartphones and tablet computers use EUI-48 addresses. EUI-64 identifiers are used in: On broadcast networks, such as Ethernet, the MAC address is expected to uniquely identify each node on that segment and allows frames to be marked for specific hosts. It thus forms
912-480: Is set to zero) is called a wildcard SSID in IEEE 802.11 standards documents, and as a no broadcast SSID or hidden SSID in the context of beacon announcements, and can be used, for example, in enterprise and mesh networks to steer a client to a particular (e.g. less utilized) access point. A station may also likewise transmit packets in which the SSID field is set to null; this prompts an associated access point to send
960-473: Is started with a MAC address set by assigning the last three bytes to be unique on the local network. While this is local administration of MAC addresses, it is not an LAA in the IEEE sense. A historical example of this hybrid situation is the DECnet protocol, where the universal MAC address (OUI AA-00-04, Digital Equipment Corporation) is administered locally. The DECnet software assigns the last three bytes for
1008-415: Is usually non-configurable, in which case it is either preset during manufacture or mathematically derived from a preset value such as a serial number or a MAC address of another network interface. As with the MAC addresses used for Ethernet devices, an infrastructure BSSID is a combination of a 24-bit organizationally unique identifier (OUI, the manufacturer's identity) and a 24-bit serial number. A BSSID with
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#17327722470291056-442: Is written in transmission order with the least significant bit of each byte transmitted first, and is used in the output of the ifconfig , ip address , and ipconfig commands, 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 the least significant bit in each byte first, while IEEE 802.5 (Token Ring) and IEEE 802.6 (FDDI) send
1104-415: The data link layer . As typically represented, MAC addresses are recognizable as six groups of two hexadecimal digits, separated by hyphens, colons, or without a separator. MAC addresses are primarily assigned by device manufacturers, and are therefore often referred to as the burned-in address , or as an Ethernet hardware address , hardware address , or physical address . Each address can be stored in
1152-399: The MAC address randomization technique vary largely in different devices. Moreover, various flaws and shortcomings in these implementations may allow an attacker to track a device even if its MAC address is changed, for instance its probe requests' other elements, or their timing. If random MAC addresses are not used, researchers have confirmed that it is possible to link a real identity to
1200-574: The US National Security Agency has a system that tracks the movements of mobile devices in a city by monitoring MAC addresses. To avert this practice, Apple has started using random MAC addresses in iOS devices while scanning for networks. Other vendors followed quickly. MAC address randomization during scanning was added in Android starting from version 6.0, Windows 10, and Linux kernel 3.18. The actual implementations of
1248-602: The assignment of a MAC address to network interface when scanning for wireless access points to avert tracking systems. In Internet Protocol (IP) networks, the MAC address of an interface corresponding to an IP address may be queried with the Address Resolution Protocol (ARP) for IPv4 and the Neighbor Discovery Protocol (NDP) for IPv6, relating OSI layer 3 addresses with layer 2 addresses. According to Edward Snowden ,
1296-482: The attached addresses to activate. Hence, various configuration scripts and utilities permit the randomization of the MAC address at the time 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 modern operating systems, such as Apple iOS and Android, especially in mobile devices, are designed to randomize
1344-408: 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 address. On most Unix -like systems, the command utility ifconfig may be used to remove and add link address aliases. For instance, the active ifconfig directive may be used on NetBSD to specify which of
1392-650: 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
1440-421: 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 forward a unicast frame to all of its ports (except the originating port), an action known as unicast flood . Only the node with the matching hardware MAC address will (normally) accept the frame; network interfaces with non-matching MAC-addresses ignore
1488-522: The complete MAC address to be AA-00-04-00-XX-YY where XX-YY reflects the DECnet network address xx.yy of the host. This eliminates the need for DECnet to have an address resolution protocol since the MAC address for any DECnet host can be determined from its DECnet address. The least significant bit of an address's first octet is referred to as the I/G , or Individual/Group , bit. When this bit
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1536-501: The first 28 bits being assigned by IEEE. The first 24 bits of the assigned MA-M block are an OUI assigned to IEEE that will not be reassigned, so the MA-M does not include assignment of an OUI. Addresses can either be universally administered addresses (UAA) or locally administered addresses (LAA). A universally administered address is uniquely assigned to a device by its manufacturer. The first three octets (in transmission order) identify
1584-485: The first octet is 06 (hexadecimal), the binary form of which is 000001 1 0, where the second-least-significant bit is 1. Therefore, it is a locally administered address. Even though many hypervisors manage dynamic MAC addresses within their own OUI , often it is useful to create an entire unique MAC within the LAA range. In virtualisation , hypervisors such as QEMU and Xen have their own OUIs. Each new virtual machine
1632-405: The first station in an ad-hoc network. However, that station does not relay traffic between the other stations; instead, the peers communicate directly with one another. Like an infrastructure BSS, an independent BSS also has a 48-bit MAC-address-like identifier. But unlike infrastructure BSS identifiers, independent BSS identifiers are not necessarily unique: the individual/group bit of the address
1680-428: 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
1728-653: The identity of previously known networks. The standard ( IEEE 802 ) format for printing EUI-48 addresses in human-friendly form 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 (e.g. 01-23-45-67-89-AB-CD-EF ). Other conventions include six groups of two hexadecimal digits separated by colons (:) (e.g. 01:23:45:67:89:AB ), and three groups of four hexadecimal digits separated by dots (.) (e.g. 0123.4567.89AB ); again in transmission order. The standard notation, also called canonical format, for MAC addresses
1776-525: The interface hardware, such as its read-only memory , or by a firmware mechanism. Many network interfaces, however, support changing their MAC addresses. The address typically includes a manufacturer's organizationally unique identifier (OUI). MAC addresses are formed according to the principles of two numbering spaces based on extended unique identifiers (EUIs) managed by the Institute of Electrical and Electronics Engineers (IEEE): EUI-48 —which replaces
1824-485: The network packets of both independent BSSs and infrastructure BSSs have a logical network service set identifier, and the logical link control does not distinguish between the use of that field to name an ESS network, and the use of that field to name a peer-to-peer ad hoc network. The two are effectively indistinguishable at the logical link control layer level. MAC address A MAC address (short for medium access control address or media access control address )
1872-742: The obsolete term MAC-48 —and EUI-64 . Network nodes with multiple network interfaces, such as routers and multilayer switches , must have a unique MAC address for each network interface in the same network. However, two network interfaces connected to two different networks can share the same MAC address. The IEEE 802 MAC address originally comes from the Xerox Network Systems Ethernet addressing scheme. This 48-bit address space contains potentially 2 (over 281 trillion) possible MAC addresses. The IEEE manages allocation of MAC addresses, originally known as MAC-48 and which it now refers to as EUI-48 identifiers. The IEEE has
1920-555: The organization that issued the identifier and are known as the organizationally unique identifier (OUI). The remainder of the address (three octets for EUI-48 or five for EUI-64) are assigned by that organization in nearly any manner they please, subject to the constraint of uniqueness. A locally administered address is assigned to a device by software or a network administrator, overriding the burned-in address for physical devices. Locally administered addresses are distinguished from universally administered addresses by setting (assigning
1968-432: The perspective of the link layer, all stations within an ESS are all on the same link, and transfer from one BSS to another is transparent to logical link control. The basic service sets formed in wireless ad hoc networks are, by definition, independent from other BSSs, and an independent BSS cannot therefore be part of an extended infrastructure. In that formal sense an independent BSS has no extended service set. However,
Service set (802.11 network) - Misplaced Pages Continue
2016-453: The range 3 3 -33-XX-XX-XX-XX (with both bits set). Given the locations of the U/L and I/G bits, they can be discerned in a single digit in common MAC address notation as shown in the following table: IEEE standard 802c further divides the locally administered MAC address block into four quadrants. This additional partitioning is called Structured Local Address Plan (SLAP) and its usage
2064-456: The station a list of supported SSIDs. Once a device has associated with a basic service set, for efficiency, the SSID is not sent within packet headers; only BSSIDs are used for addressing. Apple 's location services interpret the SSID of a Wi‑Fi access point ending in _nomap as an opt-out from being included in Apple's crowdsourced location databases. An extended service set ( ESS )
2112-461: The stations in an infrastructure-mode network, the stations in a wireless ad hoc network communicate directly with one another, i.e. without a dependence on a distribution point to relay traffic between them. In this form of peer-to-peer wireless networking, the peers form an independent basic service set ( IBSS ). Some of the responsibilities of a distribution point—such as defining network parameters and other "beaconing" functions—are established by
2160-458: The term IBSS is not used for this type of BSS but refers to the independent type discussed below.) The operating parameters of the infrastructure BSS are defined by the AP. The Wi‑Fi segments of common home and business networks are examples of this type. Each basic service set has a unique identifier, a BSSID, which is a 48-bit number that follows MAC address conventions. An infrastructure BSSID
2208-522: The value 40:D8:55 was used. The owners of an already assigned IAB may continue to use the assignment. The MA-S registry includes, for each registrant, both a 36-bit unique number used in some standards and a block of EUI-48 and EUI-64 identifiers (while the registrant of an IAB cannot assign an EUI-64). MA-S does not include assignment of an OUI. Additionally, the MA-M ( MAC address block, medium ) provides both 2 EUI-48 identifiers and 2 EUI-64 identifiers,
2256-456: The value of 1 to) the second- least-significant bit of the first octet 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, which is why this bit is 0 in all UAAs. If it is 1, the address is locally administered. In the example address 06-00-00-00-00-00
2304-595: The various context-dependent identifier number spaces, like for SNAP or EDID ), 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 property of the IEEE Registration Authority. Between 2007 and September 2012, the OUI value 00:50:C2 was used for IAB assignments. After September 2012,
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