Misplaced Pages

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88-469: IP addresses are described as consisting of two groups of bits in the address: the most significant bits are the network prefix , which identifies a whole network or subnet , and the least significant set forms the host identifier , which specifies a particular interface of a host on that network. This division is used as the basis of traffic routing between IP networks and for address allocation policies. Whereas classful network design for IPv4 sized

176-426: A / 24 as a generic description of an IPv4 network that has a 24-bit prefix and 8-bit host numbers. For example: In IPv4, CIDR notation came into wide use only after the implementation of the method, which was documented using dotted-decimal subnet mask specification after the slash, for example, 192.24.12.0 / 255.255.252.0 . Describing the network prefix width as a single number ( 192.24.12.0 / 22 )

264-438: A / 56 block for residential networks. This IPv6 subnetting reference lists the sizes for IPv6 subnetworks . Different types of network links may require different subnet sizes. The subnet mask separates the bits of the network identifier prefix from the bits of the interface identifier. Selecting a smaller prefix size results in fewer number of networks covered, but with more addresses within each network. Topologically,

352-575: A binit as an arbitrary information unit equivalent to some fixed but unspecified number of bits. RFC (identifier) A Request for Comments ( RFC ) is a publication in a series from the principal technical development and standards-setting bodies for the Internet , most prominently the Internet Engineering Task Force (IETF). An RFC is authored by individuals or groups of engineers and computer scientists in

440-409: A byte or word , is referred to, it is usually specified by a number from 0 upwards corresponding to its position within the byte or word. However, 0 can refer to either the most or least significant bit depending on the context. Similar to torque and energy in physics; information-theoretic information and data storage size have the same dimensionality of units of measurement , but there

528-450: A serial number . Once assigned a number and published, an RFC is never rescinded or modified; if the document requires amendments, the authors publish a revised document. Therefore, some RFCs supersede others; the superseded RFCs are said to be deprecated , obsolete , or obsoleted by the superseding RFC. Together, the serialized RFCs compose a continuous historical record of the evolution of Internet standards and practices. The RFC process

616-526: A common set of terms such as "MUST" and "NOT RECOMMENDED" (as defined by RFC  2119 and 8174 ), augmented Backus–Naur form (ABNF) ( RFC  5234 ) as a meta-language, and simple text-based formatting, in order to keep the RFCs consistent and easy to understand. The RFC series contains three sub-series for IETF RFCs: BCP, FYI, and STD. Best Current Practice (BCP) is a sub-series of mandatory IETF RFCs not on standards track. For Your Information (FYI)

704-613: A conducting path at a certain point of a circuit. In optical discs , a bit is encoded as the presence or absence of a microscopic pit on a reflective surface. In one-dimensional bar codes , bits are encoded as the thickness of alternating black and white lines. The bit is not defined in the International System of Units (SI). However, the International Electrotechnical Commission issued standard IEC 60027 , which specifies that

792-406: A given n -bit CIDR prefix. Shorter CIDR prefixes match more addresses, while longer prefixes match fewer. In the case of overlaid CIDR blocks, an address can match multiple CIDR prefixes of different lengths. CIDR is also used for IPv6 addresses and the syntax semantic is identical. The prefix length can range from 0 to 128, due to the larger number of bits in the address. However, by convention,

880-468: A large CIDR block containing over 2 million addresses, had been assigned by ARIN (the North American RIR) to MCI . Automation Research Systems (ARS), a Virginia VAR , leased an Internet connection from MCI and was assigned the 208.130.28.0 / 22 block, capable of addressing just over 1000 devices. ARS used a / 24 block for its publicly accessible servers, of which 208.130.29.33

968-573: A new submission which will receive a new serial number. Standards track documents are further divided into Proposed Standard and Internet Standard documents. Only the IETF, represented by the Internet Engineering Steering Group (IESG), can approve standards-track RFCs. If an RFC becomes an Internet Standard (STD), it is assigned an STD number but retains its RFC number. The definitive list of Internet Standards

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1056-431: A number of bytes which is a low power of two. A string of four bits is usually a nibble . In information theory , one bit is the information entropy of a random binary variable that is 0 or 1 with equal probability, or the information that is gained when the value of such a variable becomes known. As a unit of information , the bit is also known as a shannon , named after Claude E. Shannon . The symbol for

1144-550: A period of experimentation with various alternatives, Classless Inter-Domain Routing was based on variable-length subnet masking (VLSM), which allows each network to be divided into subnetworks of various power-of-two sizes, so that each subnetwork can be sized appropriately for local needs. Variable-length subnet masks were mentioned as one alternative in RFC   950 . Techniques for grouping addresses for common operations were based on

1232-426: A result, a / 31 network, with one binary digit in the host identifier, would be unusable, as such a subnet would provide no available host addresses after this reduction. RFC   3021 creates an exception to the "host all ones" and "host all zeros" rules to make / 31 networks usable for point-to-point links. / 32 addresses (single-host network) must be accessed by explicit routing rules, as there

1320-587: A similar fashion; BCP n refers to a certain RFC or set of RFCs, but which RFC or RFCs may change over time). An informational RFC can be nearly anything from April 1 jokes to widely recognized essential RFCs like Domain Name System Structure and Delegation ( RFC  1591 ). Some informational RFCs formed the FYI sub-series. An experimental RFC can be an IETF document or an individual submission to

1408-491: A single ISP are encouraged by IETF recommendations to obtain IP address space directly from their ISP. Networks served by multiple ISPs, on the other hand, may obtain provider-independent address space directly from the appropriate RIR. For example, in the late 1990s, the IP address 208.130.29.33 (since reassigned) was used by www.freesoft.org. An analysis of this address identified three CIDR prefixes. 208.128.0.0 / 11 ,

1496-453: A subnet on broadcast MAC layer networks always has 64-bit host identifiers. Larger prefixes (/127) are only used on some point-to-point links between routers, for security and policy reasons. The Internet Assigned Numbers Authority (IANA) issues to regional Internet registries (RIRs) large, short-prefix CIDR blocks. However, a / 8 (with over sixteen million addresses) is the largest block IANA will allocate. For example, 62.0.0.0 / 8

1584-441: Is a / 64 block, which is required for the operation of stateless address autoconfiguration . At first, the IETF recommended in RFC   3177 as a best practice that all end sites receive a / 48 address allocation, but criticism and reevaluation of actual needs and practices has led to more flexible allocation recommendations in RFC   6177 suggesting a significantly smaller allocation for some sites, such as

1672-468: Is a portmanteau of binary digit . The bit represents a logical state with one of two possible values . These values are most commonly represented as either " 1 " or " 0 " , but other representations such as true / false , yes / no , on / off , or + / − are also widely used. The relation between these values and the physical states of the underlying storage or device is a matter of convention, and different assignments may be used even within

1760-591: Is a sub-series of informational RFCs promoted by the IETF as specified in RFC ; 1150 (FYI 1). In 2011, RFC  6360 obsoleted FYI 1 and concluded this sub-series. Standard (STD) used to be the third and highest maturity level of the IETF standards track specified in RFC  2026 (BCP 9). In 2011 RFC  6410 (a new part of BCP 9) reduced the standards track to two maturity levels. There are five streams of RFCs: IETF , IRTF , IAB , independent submission , and Editorial . Only

1848-473: Is a subnet of the other. CIDR provides fine-grained routing prefix aggregation . For example, if the first 20 bits of their network prefixes match, sixteen contiguous / 24 networks can be aggregated and advertised to a larger network as a single / 20 routing table entry. This reduces the number of routes that have to be advertised. Bit The bit is the most basic unit of information in computing and digital communication . The name

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1936-474: Is administered by RIPE NCC , the European RIR. The RIRs, each responsible for a single, large, geographic area, such as Europe or North America, subdivide these blocks and allocate subnets to local Internet registries (LIRs). Similar subdividing may be repeated several times at lower levels of delegation. End-user networks receive subnets sized according to their projected short-term need. Networks served by

2024-408: Is another of the four first of what were ARPANET nodes and the source of early RFCs. The ARC became the first network information center ( InterNIC ), which was managed by Elizabeth J. Feinler to distribute the RFCs along with other network information. From 1969 until 1998, Jon Postel served as the RFC editor . On his death in 1998, his obituary was published as RFC  2468 . Following

2112-413: Is documented in RFC  2026 ( The Internet Standards Process, Revision 3 ). The RFC production process differs from the standardization process of formal standards organizations such as International Organization for Standardization (ISO). Internet technology experts may submit an Internet Draft without support from an external institution. Standards-track RFCs are published with approval from

2200-486: Is in general no meaning to adding, subtracting or otherwise combining the units mathematically, although one may act as a bound on the other. Units of information used in information theory include the shannon (Sh), the natural unit of information (nat) and the hartley (Hart). One shannon is the maximum amount of information needed to specify the state of one bit of storage. These are related by 1 Sh ≈ 0.693 nat ≈ 0.301 Hart. Some authors also define

2288-554: Is more compressed—the same bucket can hold more. For example, it is estimated that the combined technological capacity of the world to store information provides 1,300 exabytes of hardware digits. However, when this storage space is filled and the corresponding content is optimally compressed, this only represents 295 exabytes of information. When optimally compressed, the resulting carrying capacity approaches Shannon information or information entropy . Certain bitwise computer processor instructions (such as bit set ) operate at

2376-472: Is no room in such a network for a gateway. In routed subnets larger than / 31 or / 32 , the number of available host addresses is usually reduced by two, namely the largest address, which is reserved as the broadcast address, and the smallest address, which identifies the network itself. The large address size of IPv6 permitted worldwide route summarization and guaranteed sufficient address pools at each site. The standard subnet size for IPv6 networks

2464-602: Is now typical of Internet Draft documents, the precursor step before being approved as an RFC. In December 1969, researchers began distributing new RFCs via the newly operational ARPANET. RFC  1 , titled "Host Software", was written by Steve Crocker of the University of California, Los Angeles (UCLA), and published on April 7, 1969. Although written by Steve Crocker, the RFC had emerged from an early working group discussion between Steve Crocker, Steve Carr, and Jeff Rulifson . In RFC  3 , which first defined

2552-502: Is obsoleted by various newer RFCs, but SMTP itself is still "current technology", so it is not in "Historic" status. However, since BGP version 4 has entirely superseded earlier BGP versions, the RFCs describing those earlier versions, such as RFC  1267 , have been designated historic. Status unknown is used for some very old RFCs, where it is unclear which status the document would get if it were published today. Some of these RFCs would not be published at all today; an early RFC

2640-562: Is submitted as plain ASCII text and is published in that form, but may also be available in other formats . For easy access to the metadata of an RFC, including abstract, keywords, author(s), publication date, errata, status, and especially later updates, the RFC Editor site offers a search form with many features. A redirection sets some efficient parameters, example: rfc:5000. The official International Standard Serial Number (ISSN) of

2728-492: Is the Official Internet Protocol Standards. Previously STD 1 used to maintain a snapshot of the list. When an Internet Standard is updated, its STD number stays the same, now referring to a new RFC or set of RFCs. A given Internet Standard, STD n , may be RFCs x and y at a given time, but later the same standard may be updated to be RFC z instead. For example, in 2007 RFC  3700

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2816-494: Is the unit byte , coined by Werner Buchholz in June 1956, which historically was used to represent the group of bits used to encode a single character of text (until UTF-8 multibyte encoding took over) in a computer and for this reason it was used as the basic addressable element in many computer architectures . The trend in hardware design converged on the most common implementation of using eight bits per byte, as it

2904-452: Is widely used today. However, because of the ambiguity of relying on the underlying hardware design, the unit octet was defined to explicitly denote a sequence of eight bits. Computers usually manipulate bits in groups of a fixed size, conventionally named " words ". Like the byte, the number of bits in a word also varies with the hardware design, and is typically between 8 and 80 bits, or even more in some specialized computers. In

2992-692: The Internet Research Task Force (IRTF), and an independent stream from other outside sources. A new model was proposed in 2008, refined, and published in August 2009, splitting the task into several roles, including the RFC Series Advisory Group (RSAG). The model was updated in 2012. The streams were also refined in December 2009, with standards defined for their style. In January 2010, the RFC Editor function

3080-410: The yottabit (Ybit). When the information capacity of a storage system or a communication channel is presented in bits or bits per second , this often refers to binary digits, which is a computer hardware capacity to store binary data ( 0 or 1 , up or down, current or not, etc.). Information capacity of a storage system is only an upper bound to the quantity of information stored therein. If

3168-407: The 1950s and 1960s, these methods were largely supplanted by magnetic storage devices such as magnetic-core memory , magnetic tapes , drums , and disks , where a bit was represented by the polarity of magnetization of a certain area of a ferromagnetic film, or by a change in polarity from one direction to the other. The same principle was later used in the magnetic bubble memory developed in

3256-418: The 1980s, and is still found in various magnetic strip items such as metro tickets and some credit cards . In modern semiconductor memory , such as dynamic random-access memory , the two values of a bit may be represented by two levels of electric charge stored in a capacitor . In certain types of programmable logic arrays and read-only memory , a bit may be represented by the presence or absence of

3344-627: The IETF creates BCPs and RFCs on the standards track. The IAB publishes informational documents relating to policy or architecture. The IRTF publishes the results of research, either as informational documents or as experiments. Independent submissions are published at the discretion of the Independent Submissions Editor. Non-IETF documents are reviewed by the IESG for conflicts with IETF work. IRTF and independent  RFCs generally contain relevant information or experiments for

3432-568: The IETF, and are usually produced by experts participating in IETF Working Groups , which first publish an Internet Draft. This approach facilitates initial rounds of peer review before documents mature into RFCs. The RFC tradition of pragmatic, experience-driven, after-the-fact standards authorship accomplished by individuals or small working groups can have important advantages over the more formal, committee-driven process typical of ISO and national standards bodies. Most RFCs use

3520-633: The Internet at large not in conflict with IETF work. compare RFC  4846 , 5742 and 5744 . The Editorial Stream is used to effect editorial policy changes across the RFC series (see RFC  9280 ). The official source for RFCs on the World Wide Web is the RFC Datatracker. Almost any published RFC can be retrieved via a URL of the form https://datatracker.ietf.org/doc/html/rfc5000, shown for RFC  5000 . Every RFC

3608-669: The Internet community, other documents also called requests for comments have been published, as in U.S. Federal government work, such as the National Highway Traffic Safety Administration . The inception of the RFC format occurred in 1969 as part of the seminal ARPANET project. Today, it is the official publication channel for the Internet Engineering Task Force (IETF), the Internet Architecture Board (IAB), and – to some extent –

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3696-413: The Internet to be reprogrammed in small ways—no small feat at a time when the Internet was entering a period of rapid growth. In 1993, the Internet Engineering Task Force published a new set of standards, RFC   1518 and RFC   1519 , to define this new principle for allocating IP address blocks and routing IPv4 packets. An updated version, RFC   4632 , was published in 2006. After

3784-436: The RFC Editor. A draft is designated experimental if it is unclear the proposal will work as intended or unclear if the proposal will be widely adopted. An experimental RFC may be promoted to standards track if it becomes popular and works well. The Best Current Practice subseries collects administrative documents and other texts which are considered as official rules and not only informational , but which do not affect over

3872-826: The RFC Series Approval Board (RSAB). It also established a new Editorial Stream for the RFC Series and concluded the RSOC. The role of the RSE was changed to the RFC Series Consulting Editor (RSCE). In September 2022, Alexis Rossi was appointed to that position. Requests for Comments were originally produced in non- reflowable text format. In August 2019, the format was changed so that new documents can be viewed optimally in devices with varying display sizes. The RFC Editor assigns each RFC

3960-451: The RFC series is 2070-1721. Not all RFCs are standards. Each RFC is assigned a designation with regard to status within the Internet standardization process. This status is one of the following: Informational , Experimental , Best Current Practice , Standards Track , or Historic . Once submitted, accepted, and published, an RFC cannot be changed. Errata may be submitted, which are published separately. More significant changes require

4048-696: The RFC series, Crocker started attributing the RFC series to the Network Working Group. Rather than being a formal committee, it was a loose association of researchers interested in the ARPANET project. In effect, it included anyone who wanted to join the meetings and discussions about the project. Many of the subsequent RFCs of the 1970s also came from UCLA, because UCLA is one of the first of what were Interface Message Processors (IMPs) on ARPANET. The Augmentation Research Center (ARC) at Stanford Research Institute , directed by Douglas Engelbart ,

4136-504: The address. When emphasizing only the size of a network, the address portion of the notation is usually omitted. Thus, a /20 block is a CIDR block with an unspecified 20-bit prefix. An IP address is part of a CIDR block and is said to match the CIDR prefix if the initial n bits of the address and the CIDR prefix are the same. An IPv4 address is 32 bits so an n -bit CIDR prefix leaves 32 − n bits unmatched, meaning that 2 IPv4 addresses match

4224-424: The average. This principle is the basis of data compression technology. Using an analogy, the hardware binary digits refer to the amount of storage space available (like the number of buckets available to store things), and the information content the filling, which comes in different levels of granularity (fine or coarse, that is, compressed or uncompressed information). When the granularity is finer—when information

4312-679: The binary digit is either "bit", per the IEC 80000-13 :2008 standard, or the lowercase character "b", per the IEEE 1541-2002 standard. Use of the latter may create confusion with the capital "B" which is the international standard symbol for the byte. The encoding of data by discrete bits was used in the punched cards invented by Basile Bouchon and Jean-Baptiste Falcon (1732), developed by Joseph Marie Jacquard (1804), and later adopted by Semyon Korsakov , Charles Babbage , Herman Hollerith , and early computer manufacturers like IBM . A variant of that idea

4400-460: The binary representation of their IP addresses. IPv4 CIDR blocks are identified using a syntax similar to that of IPv4 addresses: a dotted-decimal address, followed by a slash, then a number from 0 to 32, i.e., a.b.c.d / n . The dotted decimal portion is the IPv4 address. The number following the slash is the prefix length, the number of shared initial bits, counting from the most-significant bit of

4488-466: The classful network method was found not scalable . This led to the development of subnetting and CIDR. The formerly meaningful class distinctions based on the most-significant address bits were abandoned and the new system was described as classless , in contrast to the old system, which became known as classful . Routing protocols were revised to carry not just IP addresses, but also their subnet masks. Implementing CIDR required every host and router on

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4576-407: The concept of cluster addressing, first proposed by Carl-Herbert Rokitansky. CIDR notation is a compact representation of an IP address and its associated network mask. The notation was invented by Phil Karn in the 1980s. CIDR notation specifies an IP address, a slash ('/') character, and a decimal number. The decimal number is the count of consecutive leading 1 -bits (from left to right) in

4664-415: The early 21st century, retail personal or server computers have a word size of 32 or 64 bits. The International System of Units defines a series of decimal prefixes for multiples of standardized units which are commonly also used with the bit and the byte. The prefixes kilo (10 ) through yotta (10 ) increment by multiples of one thousand, and the corresponding units are the kilobit (kbit) through

4752-457: The electrical state of a flip-flop circuit. For devices using positive logic , a digit value of 1 (or a logical value of true) is represented by a more positive voltage relative to the representation of 0 . Different logic families require different voltages, and variations are allowed to account for component aging and noise immunity. For example, in transistor–transistor logic (TTL) and compatible circuits, digit values 0 and 1 at

4840-648: The expiration of the original ARPANET contract with the U.S. federal government, the Internet Society, acting on behalf of the IETF, contracted with the Networking Division of the University of Southern California (USC) Information Sciences Institute (ISI) to assume the editorship and publishing responsibilities under the direction of the IAB. Sandy Ginoza joined USC/ISI in 1999 to work on RFC editing, and Alice Hagens in 2005. Bob Braden took over

4928-402: The fixed-length prefixing of the previous classful network design). The main benefit of this is that it grants finer control of the sizes of subnets allocated to organizations, hence slowing the exhaustion of IPv4 addresses from allocating larger subnets than needed. CIDR gave rise to a new way of writing IP addresses known as CIDR notation, in which an IP address is followed by a suffix indicating

5016-460: The form of a memorandum describing methods, behaviors, research, or innovations applicable to the working of the Internet and Internet-connected systems. It is submitted either for peer review or to convey new concepts, information, or, occasionally, engineering humor. The IETF adopts some of the proposals published as RFCs as Internet Standards . However, many RFCs are informational or experimental in nature and are not standards. The RFC system

5104-490: The global community of computer network researchers in general. The authors of the first RFCs typewrote their work and circulated hard copies among the ARPA researchers. Unlike the modern RFCs, many of the early RFCs were actual Requests for Comments and were titled as such to avoid sounding too declarative and to encourage discussion. The RFC leaves questions open and is written in a less formal style. This less formal style

5192-491: The leased line serving ARS. Only within the ARS corporate network would the 208.130.29.0 / 24 prefix have been used. In common usage, the first address in a subnet, all binary zero in the host identifier, is reserved for referring to the network itself, while the last address, all binary one in the host identifier, is used as a broadcast address for the network; this reduces the number of addresses available for hosts by 2. As

5280-409: The level of manipulating bits rather than manipulating data interpreted as an aggregate of bits. In the 1980s, when bitmapped computer displays became popular, some computers provided specialized bit block transfer instructions to set or copy the bits that corresponded to a given rectangular area on the screen. In most computers and programming languages, when a bit within a group of bits, such as

5368-580: The lower n {\displaystyle n} bits set to 0. (For IPv6, substitute 128.) For a fixed n {\displaystyle n} , the set of all X / n {\displaystyle X/n} subnets constitute a partition , that is a cover of non-overlapping sets. Increasing n {\displaystyle n} yields finer and finer subpartitions. Thus two subnets X / n {\displaystyle X/n} and Y / m {\displaystyle Y/m} are either disjoint or one

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5456-429: The mask must be left contiguous. Given this constraint, a subnet mask and CIDR notation serve exactly the same function. CIDR is principally a bitwise, prefix-based standard for the representation of IP addresses and their routing properties. It facilitates routing by allowing blocks of addresses to be grouped into single routing table entries. These groups, commonly called CIDR blocks, share an initial sequence of bits in

5544-557: The network mask. Each 1-bit denotes a bit of the address range which must remain identical to the given IP address. The IP address in CIDR notation is always represented according to the standards for IPv4 or IPv6. The address may denote a specific interface address (including a host identifier, such as 10.0.0.1 / 8 ), or it may be the beginning address of an entire network (using a host identifier of 0, as in 10.0.0.0 / 8 or its equivalent 10 / 8 ). CIDR notation can even be used with no IP address at all, e.g. when referring to

5632-484: The network prefix as one or more 8-bit groups, resulting in the blocks of Class A, B, or C addresses, under CIDR address space is allocated to Internet service providers and end users on any address-bit boundary. In IPv6 , however, the interface identifier has a fixed size of 64 bits by convention, and smaller subnets are never allocated to end users. CIDR is based on variable-length subnet masking ( VLSM ), in which network prefixes have variable length (as opposed to

5720-421: The number of bits of the prefix. Some examples of CIDR notation are the addresses 192.0.2.0 / 24 for IPv4 and 2001:db8:: / 32 for IPv6. Blocks of addresses having contiguous prefixes may be aggregated as supernets , reducing the number of entries in the global routing table. Each IP address consists of a network prefix followed by a host identifier. In the classful network architecture of IPv4 ,

5808-471: The only other size (2) provided far too many, more than 16 million. This led to inefficiencies in address use as well as inefficiencies in routing, because it required a large number of allocated class-C networks with individual route announcements, being geographically dispersed with little opportunity for route aggregation . Within a decade after the invention of the Domain Name System (DNS),

5896-473: The output of a device are represented by no higher than 0.4 V and no lower than 2.6 V, respectively; while TTL inputs are specified to recognize 0.8 V or below as 0 and 2.2 V or above as 1 . Bits are transmitted one at a time in serial transmission , and by a multiple number of bits in parallel transmission . A bitwise operation optionally processes bits one at a time. Data transfer rates are usually measured in decimal SI multiples of

5984-518: The prefix length associated with an IPv4 address or network in quad-dotted notation: 32 bits, starting with a number of 1 -bits equal to the prefix length, ending with 0 -bits, and encoded in four-part dotted-decimal format: 255.255.255.0 . A subnet mask encodes the same information as a prefix length but predates the advent of CIDR. In CIDR notation, the prefix bits are always contiguous. Subnet masks were allowed by RFC   950 to specify non-contiguous bits until RFC   4632 stated that

6072-638: The program were included the RFC Editor Model (Version 3) as defined in RFC  9280 , published in June 2022. Generally, the new model is intended to clarify responsibilities and processes for defining and implementing policies related to the RFC series and the RFC Editor function. Changes in the new model included establishing the position of the RFC Consulting Editor, the RFC Series Working Group (RSWG), and

6160-427: The recommendation to use source filtering to make DoS attacks more difficult ( RFC  2827 : " Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing ") is BCP 38 . A historic RFC is one that the technology defined by the RFC is no longer recommended for use, which differs from "Obsoletes" header in a replacement RFC. For example, RFC  821 ( SMTP ) itself

6248-429: The role of RFC project lead, while Joyce K. Reynolds continued to be part of the team until October 13, 2006. In July 2007, streams of RFCs were defined, so that the editing duties could be divided. IETF documents came from IETF working groups or submissions sponsored by an IETF area director from the Internet Engineering Steering Group . The IAB can publish its own documents. A research stream of documents comes from

6336-415: The same device or program . It may be physically implemented with a two-state device. A contiguous group of binary digits is commonly called a bit string , a bit vector, or a single-dimensional (or multi-dimensional) bit array . A group of eight bits is called one  byte , but historically the size of the byte is not strictly defined. Frequently, half, full, double and quadruple words consist of

6424-656: The set of subnets described by CIDR represent a cover of the corresponding address space. The interval described by the notation X / n {\displaystyle X/n} numerically corresponds to addresses of the form (for IPv4) [ x ⋅ 2 32 − n , x ⋅ 2 32 − n + 2 32 − n − 1 ] {\displaystyle [x\cdot 2^{32-n},x\cdot 2^{32-n}+2^{32-n}-1]} , where X = x ⋅ 2 32 − n {\displaystyle X=x\cdot 2^{32-n}} has

6512-415: The states of electrical relays which could be either "open" or "closed". When relays were replaced by vacuum tubes , starting in the 1940s, computer builders experimented with a variety of storage methods, such as pressure pulses traveling down a mercury delay line , charges stored on the inside surface of a cathode-ray tube , or opaque spots printed on glass discs by photolithographic techniques. In

6600-554: The symbol for binary digit should be 'bit', and this should be used in all multiples, such as 'kbit', for kilobit. However, the lower-case letter 'b' is widely used as well and was recommended by the IEEE 1541 Standard (2002) . In contrast, the upper case letter 'B' is the standard and customary symbol for byte. Multiple bits may be expressed and represented in several ways. For convenience of representing commonly reoccurring groups of bits in information technology, several units of information have traditionally been used. The most common

6688-783: The three most significant bits of the 32-bit IP address defined the size of the network prefix for unicast networking, and determined the network class A, B, or C. The advantage of this system is that the network prefix could be determined for any IP address without any further information. The disadvantage is that networks were usually too big or too small for most organizations to use, because only three sizes were available. The smallest allocation and routing block contained 2 = 256 addresses, larger than necessary for personal or department networks, but too small for most enterprises. The next larger block contained 2 = 65 536 addresses, too large to be used efficiently even by large organizations. But for network users who needed more than 65 536 addresses,

6776-556: The two possible values of one bit of storage are not equally likely, that bit of storage contains less than one bit of information. If the value is completely predictable, then the reading of that value provides no information at all (zero entropic bits, because no resolution of uncertainty occurs and therefore no information is available). If a computer file that uses n  bits of storage contains only m  <  n  bits of information, then that information can in principle be encoded in about m  bits, at least on

6864-462: The two stable states of a flip-flop , two positions of an electrical switch , two distinct voltage or current levels allowed by a circuit , two distinct levels of light intensity , two directions of magnetization or polarization , the orientation of reversible double stranded DNA , etc. Bits can be implemented in several forms. In most modern computing devices, a bit is usually represented by an electrical voltage or current pulse, or by

6952-507: The unit bit per second (bit/s), such as kbit/s. In the earliest non-electronic information processing devices, such as Jacquard's loom or Babbage's Analytical Engine , a bit was often stored as the position of a mechanical lever or gear, or the presence or absence of a hole at a specific point of a paper card or tape . The first electrical devices for discrete logic (such as elevator and traffic light control circuits , telephone switches , and Konrad Zuse's computer) represented bits as

7040-477: The use of a logarithmic measure of information in 1928. Claude E. Shannon first used the word "bit" in his seminal 1948 paper " A Mathematical Theory of Communication ". He attributed its origin to John W. Tukey , who had written a Bell Labs memo on 9 January 1947 in which he contracted "binary information digit" to simply "bit". A bit can be stored by a digital device or other physical system that exists in either of two possible distinct states . These may be

7128-572: The wire data . The border between standards track and BCP is often unclear. If a document only affects the Internet Standards Process, like BCP 9, or IETF administration, it is clearly a BCP. If it only defines rules and regulations for Internet Assigned Numbers Authority (IANA) registries it is less clear; most of these documents are BCPs, but some are on the standards track. The BCP series also covers technical recommendations for how to practice Internet standards; for instance,

7216-449: Was an Internet Standard—STD 1—and in May 2008 it was replaced with RFC  5000 , so RFC  3700 changed to Historic , RFC  5000 became an Internet Standard, and as of May 2008 STD 1 is RFC  5000 . as of December 2013 RFC  5000 is replaced by RFC  7100 , updating RFC  2026 to no longer use STD 1. (Best Current Practices work in

7304-421: Was easier for network administrators to conceptualize and to calculate. It became gradually incorporated into later standards documents and into network configuration interfaces. The number of addresses of a network may be calculated as 2, where address length is 128 for IPv6 and 32 for IPv4. For example, in IPv4, the prefix length / 29 gives: 2 = 2 = 8 addresses. A subnet mask is a bitmask that encodes

7392-416: Was invented by Steve Crocker in 1969 to help record unofficial notes on the development of ARPANET . RFCs have since become official documents of Internet specifications , communications protocols , procedures, and events. According to Crocker, the documents "shape the Internet's inner workings and have played a significant role in its success," but are not widely known outside the community. Outside of

7480-493: Was moved to a contractor, Association Management Solutions, with Glenn Kowack serving as interim series editor. In late 2011, Heather Flanagan was hired as the permanent RFC Series Editor (RSE). Also at that time, an RFC Series Oversight Committee (RSOC) was created. In 2020, the IAB convened the RFC Editor Future Development program to discuss potential changes to the RFC Editor model. The results of

7568-458: Was often just that: a simple Request for Comments, not intended to specify a protocol, administrative procedure, or anything else for which the RFC series is used today. The general rule is that original authors (or their employers, if their employment conditions so stipulate) retain copyright unless they make an explicit transfer of their rights. An independent body, the IETF Trust, holds

7656-452: Was one. All of these CIDR prefixes would be used, at different locations in the network. Outside MCI's network, the 208.128.0.0 / 11 prefix would be used to direct to MCI traffic bound not only for 208.130.29.33 , but also for any of the roughly two million IP addresses with the same initial 11 bits. Within MCI's network, 208.130.28.0 / 22 would become visible, directing traffic to

7744-469: Was the perforated paper tape . In all those systems, the medium (card or tape) conceptually carried an array of hole positions; each position could be either punched through or not, thus carrying one bit of information. The encoding of text by bits was also used in Morse code (1844) and early digital communications machines such as teletypes and stock ticker machines (1870). Ralph Hartley suggested

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