The JANET NRS ( Name Registration Scheme ) was a pseudo-hierarchical naming scheme used on British academic and research networks in the 1980s. Its purpose was to organise and manage domain names within the JANET network, contributing to the establishment of computer networking familiarities at universities in the United Kingdom and other academic and research institutions. It used a reverse domain name notation .
96-553: It was proposed in 1983 and used until the superficially similar Internet Domain Name System (DNS) was fully adopted. The JANET NRS was developed to allocate and maintain unique domain names for organisations connected to the JANET network. Its primary purpose was to ensure a standardised and organised approach to domain name registration, facilitating identification and differentiation of institutions and their computer resources on
192-645: A de facto standard in the industry. In May 2005, the IETF defined a formal standard for it. An IP address conflict occurs when two devices on the same local physical or wireless network claim to have the same IP address. A second assignment of an address generally stops the IP functionality of one or both of the devices. Many modern operating systems notify the administrator of IP address conflicts. When IP addresses are assigned by multiple people and systems with differing methods, any of them may be at fault. If one of
288-478: A computer network that uses the Internet Protocol for communication. IP addresses serve two main functions: network interface identification , and location addressing . Internet Protocol version 4 (IPv4) was the first standalone specification for the IP address, and has been in use since 1983. IPv4 addresses are defined as a 32-bit number, which became too small to provide enough addresses as
384-446: A label and zero or more resource records (RR), which hold information associated with the domain name. The domain name itself consists of the label, concatenated with the name of its parent node on the right, separated by a dot. The tree sub-divides into zones beginning at the root zone . A DNS zone may consist of as many domains and subdomains as the zone manager chooses. DNS can also be partitioned according to class where
480-408: A static IP address . In contrast, when a computer's IP address is assigned each time it restarts, this is known as using a dynamic IP address . Dynamic IP addresses are assigned by network using Dynamic Host Configuration Protocol (DHCP). DHCP is the most frequently used technology for assigning addresses. It avoids the administrative burden of assigning specific static addresses to each device on
576-435: A "com" server, and finally an "example.com" server. Name servers in delegations are identified by name, rather than by IP address. This means that a resolving name server must issue another DNS request to find out the IP address of the server to which it has been referred. If the name given in the delegation is a subdomain of the domain for which the delegation is being provided, there is a circular dependency . In this case,
672-408: A cache of data. An authoritative name server can either be a primary server or a secondary server. Historically the terms master/slave and primary/secondary were sometimes used interchangeably but the current practice is to use the latter form. A primary server is a server that stores the original copies of all zone records. A secondary server uses a special automatic updating mechanism in
768-416: A combination of these methods. In a non-recursive query , a DNS resolver queries a DNS server that provides a record either for which the server is authoritative, or it provides a partial result without querying other servers. In case of a caching DNS resolver , the non-recursive query of its local DNS cache delivers a result and reduces the load on upstream DNS servers by caching DNS resource records for
864-755: A compromise between five competing proposals of solutions to Paul Mockapetris . Mockapetris instead created the Domain Name System in 1983 while at the University of Southern California . The Internet Engineering Task Force published the original specifications in RFC 882 and RFC 883 in November 1983. These were updated in RFC 973 in January 1986. In 1984, four UC Berkeley students, Douglas Terry, Mark Painter, David Riggle, and Songnian Zhou, wrote
960-399: A dataset from a reliable source. Assuming the resolver has no cached records to accelerate the process, the resolution process starts with a query to one of the root servers. In typical operation, the root servers do not answer directly, but respond with a referral to more authoritative servers, e.g., a query for "www.wikipedia.org" is referred to the org servers. The resolver now queries
1056-401: A dynamically assigned IP address that seldom changes. IPv4 addresses, for example, are usually assigned with DHCP, and a DHCP service can use rules that maximize the chance of assigning the same address each time a client asks for an assignment. In IPv6, a prefix delegation can be handled similarly, to make changes as rare as feasible. In a typical home or small-office setup, a single router
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#17327809654451152-539: A general purpose database, the DNS has also been used in combating unsolicited email (spam) by storing a real-time blackhole list (RBL). The DNS database is traditionally stored in a structured text file, the zone file , but other database systems are common. The Domain Name System originally used the User Datagram Protocol (UDP) as transport over IP. Reliability, security, and privacy concerns spawned
1248-531: A group of 8 bits (an octet ) of the address. In some cases of technical writing, IPv4 addresses may be presented in various hexadecimal , octal , or binary representations. In the early stages of development of the Internet Protocol, the network number was always the highest order octet (most significant eight bits). Because this method allowed for only 256 networks, it soon proved inadequate as additional networks developed that were independent of
1344-456: A home network an unchanging address, it is more likely to be abused by customers who host websites from home, or by hackers who can try the same IP address over and over until they breach a network. Multiple client devices can appear to share an IP address, either because they are part of a shared web hosting service environment or because an IPv4 network address translator (NAT) or proxy server acts as an intermediary agent on behalf of
1440-672: A large address space, there is no need to have complex address conservation methods as used in CIDR. All modern desktop and enterprise server operating systems include native support for IPv6 , but it is not yet widely deployed in other devices, such as residential networking routers, voice over IP (VoIP) and multimedia equipment, and some networking hardware . Just as IPv4 reserves addresses for private networks, blocks of addresses are set aside in IPv6. In IPv6, these are referred to as unique local addresses (ULAs). The routing prefix fc00:: / 7
1536-489: A link. This feature is used in the lower layers of IPv6 network administration, such as for the Neighbor Discovery Protocol . Private and link-local address prefixes may not be routed on the public Internet. IP addresses are assigned to a host either dynamically as they join the network, or persistently by configuration of the host hardware or software. Persistent configuration is also known as using
1632-493: A network in one transmission operation as an all-hosts broadcast . All receivers capture the network packet. The address 255.255.255.255 is used for network broadcast. In addition, a more limited directed broadcast uses the all-ones host address with the network prefix. For example, the destination address used for directed broadcast to devices on the network 192.0.2.0 / 24 is 192.0.2.255 . IPv6 does not implement broadcast addressing and replaces it with multicast to
1728-478: A network. It also allows devices to share the limited address space on a network if only some of them are online at a particular time. Typically, dynamic IP configuration is enabled by default in modern desktop operating systems. The address assigned with DHCP is associated with a lease and usually has an expiration period. If the lease is not renewed by the host before expiry, the address may be assigned to another device. Some DHCP implementations attempt to reassign
1824-407: A period of time after an initial response from upstream DNS servers. In a recursive query , a DNS resolver queries a single DNS server, which may in turn query other DNS servers on behalf of the requester. For example, a simple stub resolver running on a home router typically makes a recursive query to the DNS server run by the user's ISP . A recursive query is one for which the DNS server answers
1920-469: A service's location on the network to change without affecting the end users, who continue to use the same hostname. Users take advantage of this when they use meaningful Uniform Resource Locators ( URLs ) and e-mail addresses without having to know how the computer actually locates the services. An important and ubiquitous function of the DNS is its central role in distributed Internet services such as cloud services and content delivery networks . When
2016-637: A significant part of the history of network infrastructure and academic networking in the UK. The one remaining legacy of the NRS is the convention of using .uk for the Internet country code top-level domain (ccTLD), rather than .gb as specified by ISO 3166 . The UK was the only country with a pre-existing national standard. Domain Name System Early research and development: Merging
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#17327809654452112-513: A single sender or a single receiver, and can be used for both sending and receiving. Usually, a unicast address is associated with a single device or host, but a device or host may have more than one unicast address. Sending the same data to multiple unicast addresses requires the sender to send all the data many times over, once for each recipient. Broadcasting is an addressing technique available in IPv4 to address data to all possible destinations on
2208-420: A time to live (TTL), which indicates how long the information remains valid before it needs to be discarded or refreshed. This TTL is determined by the administrator of the authoritative DNS server and can range from a few seconds to several days or even weeks. IP address An Internet Protocol address ( IP address ) is a numerical label such as 192.0.2.1 that is assigned to a device connected to
2304-477: A type of error called a "lame delegation" or "lame response". Domain name resolvers determine the domain name servers responsible for the domain name in question by a sequence of queries starting with the right-most (top-level) domain label. For proper operation of its domain name resolver, a network host is configured with an initial cache ( hints ) of the known addresses of the root name servers. The hints are updated periodically by an administrator by retrieving
2400-458: A user accesses a distributed Internet service using a URL, the domain name of the URL is translated to the IP address of a server that is proximal to the user. The key functionality of the DNS exploited here is that different users can simultaneously receive different translations for the same domain name, a key point of divergence from a traditional phone-book view of the DNS. This process of using
2496-426: Is a built-in feature of IPv6. In IPv4, anycast addressing is implemented with Border Gateway Protocol using the shortest-path metric to choose destinations. Anycast methods are useful for global load balancing and are commonly used in distributed DNS systems. A host may use geolocation to deduce the geographic position of its communicating peer. This is typically done by retrieving geolocation info about
2592-435: Is defined for the special use of link-local addressing for IPv4 networks. In IPv6, every interface, whether using static or dynamic addresses, also receives a link-local address automatically in the block fe80:: / 10 . These addresses are only valid on the link, such as a local network segment or point-to-point connection, to which a host is connected. These addresses are not routable and, like private addresses, cannot be
2688-492: Is known as the LDH rule (letters, digits, hyphen). Domain names are interpreted in a case-independent manner. Labels may not start or end with a hyphen. An additional rule requires that top-level domain names should not be all-numeric. The limited set of ASCII characters permitted in the DNS prevented the representation of names and words of many languages in their native alphabets or scripts. To make this possible, ICANN approved
2784-488: Is only achieved with at least 6 labels (counting the last null label). Although no technical limitation exists to prevent domain name labels from using any character that is representable by an octet, hostnames use a preferred format and character set. The characters allowed in labels are a subset of the ASCII character set, consisting of characters a through z , A through Z , digits 0 through 9 , and hyphen. This rule
2880-416: Is recognized as consisting of two parts: the network prefix in the high-order bits and the remaining bits called the rest field , host identifier , or interface identifier (IPv6), used for host numbering within a network. The subnet mask or CIDR notation determines how the IP address is divided into network and host parts. The term subnet mask is only used within IPv4. Both IP versions however use
2976-421: Is reserved for this block, which is divided into two / 8 blocks with different implied policies. The addresses include a 40-bit pseudorandom number that minimizes the risk of address collisions if sites merge or packets are misrouted. Early practices used a different block for this purpose ( fec0:: ), dubbed site-local addresses. However, the definition of what constituted a site remained unclear and
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3072-399: Is served by the root name servers , the servers to query when looking up ( resolving ) a TLD . An authoritative name server is a name server that only gives answers to DNS queries from data that have been configured by an original source, for example, the domain administrator or by dynamic DNS methods, in contrast to answers obtained via a query to another name server that only maintains
3168-662: Is the only device visible to an Internet service provider (ISP), and the ISP may try to provide a configuration that is as stable as feasible, i.e. sticky . On the local network of the home or business, a local DHCP server may be designed to provide sticky IPv4 configurations, and the ISP may provide a sticky IPv6 prefix delegation, giving clients the option to use sticky IPv6 addresses. Sticky should not be confused with static ; sticky configurations have no guarantee of stability, while static configurations are used indefinitely and only changed deliberately. Address block 169.254.0.0 / 16
3264-551: The Internationalizing Domain Names in Applications (IDNA) system, by which user applications, such as web browsers, map Unicode strings into the valid DNS character set using Punycode . In 2009, ICANN approved the installation of internationalized domain name country code top-level domains ( ccTLD s) . In addition, many registries of the existing top-level domain names ( TLD s ) have adopted
3360-486: The Internet Engineering Task Force (IETF) to explore new technologies to expand addressing capability on the Internet. The result was a redesign of the Internet Protocol which became eventually known as Internet Protocol Version 6 (IPv6) in 1995. IPv6 technology was in various testing stages until the mid-2000s when commercial production deployment commenced. Today, these two versions of
3456-477: The Point-to-Point Protocol . Computers and equipment used for the network infrastructure, such as routers and mail servers, are typically configured with static addressing. In the absence or failure of static or dynamic address configurations, an operating system may assign a link-local address to a host using stateless address autoconfiguration. Sticky is an informal term used to describe
3552-478: The top-level domain ; for example, the domain name www.example.com belongs to the top-level domain com . The hierarchy of domains descends from right to left; each label to the left specifies a subdivision, or subdomain of the domain to the right. For example, the label example specifies a subdomain of the com domain, and www is a subdomain of example.com. This tree of subdivisions may have up to 127 levels. A label may contain zero to 63 characters, because
3648-404: The " Authoritative Answer " ( AA ) bit in its responses. This flag is usually reproduced prominently in the output of DNS administration query tools, such as dig , to indicate that the responding name server is an authority for the domain name in question. When a name server is designated as the authoritative server for a domain name for which it does not have authoritative data, it presents
3744-540: The ARPANET. Elizabeth Feinler developed and maintained the first ARPANET directory. Maintenance of numerical addresses, called the Assigned Numbers List, was handled by Jon Postel at the University of Southern California 's Information Sciences Institute (ISI), whose team worked closely with SRI. Addresses were assigned manually. Computers, including their hostnames and addresses, were added to
3840-415: The CIDR concept and notation. In this, the IP address is followed by a slash and the number (in decimal) of bits used for the network part, also called the routing prefix . For example, an IPv4 address and its subnet mask may be 192.0.2.1 and 255.255.255.0 , respectively. The CIDR notation for the same IP address and subnet is 192.0.2.1 / 24 , because the first 24 bits of the IP address indicate
3936-462: The DNS database are for start of authority ( SOA ), IP addresses ( A and AAAA ), SMTP mail exchangers (MX), name servers (NS), pointers for reverse DNS lookups (PTR), and domain name aliases (CNAME). Although not intended to be a general purpose database, DNS has been expanded over time to store records for other types of data for either automatic lookups, such as DNSSEC records, or for human queries such as responsible person (RP) records. As
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4032-401: The DNS protocol in communication with its primary to maintain an identical copy of the primary records. Every DNS zone must be assigned a set of authoritative name servers. This set of servers is stored in the parent domain zone with name server (NS) records. An authoritative server indicates its status of supplying definitive answers, deemed authoritative , by setting a protocol flag, called
4128-417: The DNS to assign proximal servers to users is key to providing faster and more reliable responses on the Internet and is widely used by most major Internet services. The DNS reflects the structure of administrative responsibility on the Internet. Each subdomain is a zone of administrative autonomy delegated to a manager. For zones operated by a registry , administrative information is often complemented by
4224-467: The DNS was the concept of context to name lookups, e.g. 'mail' or 'file transfer'. This made the NRS more sophisticated than the DNS, permitting overloading of names. JANET transitioned to using Internet protocols in 1991, and by 1994 the DNS had become the de facto standard for domain names on JANET. The final mail gateway was taken out of service by the end of 1997. Nonetheless, the JANET NRS remains
4320-460: The IDNA system, guided by RFC 5890, RFC 5891, RFC 5892, RFC 5893. The Domain Name System is maintained by a distributed database system, which uses the client–server model . The nodes of this database are the name servers . Each domain has at least one authoritative DNS server that publishes information about that domain and the name servers of any domains subordinate to it. The top of the hierarchy
4416-430: The IP address spaces . The Domain Name System maintains the domain name hierarchy and provides translation services between it and the address spaces. Internet name servers and a communication protocol implement the Domain Name System. A DNS name server is a server that stores the DNS records for a domain; a DNS name server responds with answers to queries against its database. The most common types of records stored in
4512-422: The IP address of the other node from a database. A public IP address is a globally routable unicast IP address, meaning that the address is not an address reserved for use in private networks , such as those reserved by RFC 1918 , or the various IPv6 address formats of local scope or site-local scope, for example for link-local addressing. Public IP addresses may be used for communication between hosts on
4608-431: The Internet Protocol are in simultaneous use. Among other technical changes, each version defines the format of addresses differently. Because of the historical prevalence of IPv4, the generic term IP address typically still refers to the addresses defined by IPv4. The gap in version sequence between IPv4 and IPv6 resulted from the assignment of version 5 to the experimental Internet Stream Protocol in 1979, which however
4704-402: The Internet, and increase performance in end-user applications, the Domain Name System supports DNS cache servers which store DNS query results for a period of time determined in the configuration ( time-to-live ) of the domain name record in question. Typically, such caching DNS servers also implement the recursive algorithm necessary to resolve a given name starting with the DNS root through to
4800-468: The Internet, but it lacked scalability in the face of the rapid expansion of networking in the 1990s. The class system of the address space was replaced with Classless Inter-Domain Routing (CIDR) in 1993. CIDR is based on variable-length subnet masking (VLSM) to allow allocation and routing based on arbitrary-length prefixes. Today, remnants of classful network concepts function only in a limited scope as
4896-500: The Internet, such as factory machines that communicate only with each other via TCP/IP , need not have globally unique IP addresses. Today, such private networks are widely used and typically connect to the Internet with network address translation (NAT), when needed. Three non-overlapping ranges of IPv4 addresses for private networks are reserved. These addresses are not routed on the Internet and thus their use need not be coordinated with an IP address registry. Any user may use any of
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#17327809654454992-414: The NRS. A principal difference with the Domain Name System was that the order of significance began with the most significant part (so called big-endian addresses). Also, NRS names were canonically written in upper case. For example, the University of Cambridge had the NRS name UK.AC.CAM , whereas its DNS domain is cam.ac.uk . After Internet top-level domains were introduced from 1984, confusion
5088-645: The RIRs, which are responsible for distributing them to local Internet registries in their region such as internet service providers (ISPs) and large institutions. Some addresses are reserved for private networks and are not globally unique. Within a network, the network administrator assigns an IP address to each device. Such assignments may be on a static (fixed or permanent) or dynamic basis, depending on network practices and software features. Some jurisdictions consider IP addresses to be personal data . An IP address serves two principal functions: it identifies
5184-576: The address should be treated as a routing prefix. For example, 192.0.2.1 / 24 indicates that 24 significant bits of the address are the prefix, with the remaining 8 bits used for host addressing. This is equivalent to the historically used subnet mask (in this case, 255.255.255.0 ). The IP address space is managed globally by the Internet Assigned Numbers Authority (IANA) and the five regional Internet registries (RIRs). IANA assigns blocks of IP addresses to
5280-704: The associated entities. Most prominently, it translates readily memorized domain names to the numerical IP addresses needed for locating and identifying computer services and devices with the underlying network protocols . The Domain Name System has been an essential component of the functionality of the Internet since 1985. The Domain Name System delegates the responsibility of assigning domain names and mapping those names to Internet resources by designating authoritative name servers for each domain. Network administrators may delegate authority over subdomains of their allocated name space to other name servers. This mechanism provides distributed and fault-tolerant service and
5376-543: The authoritative name servers of the queried domain. With this function implemented in the name server, user applications gain efficiency in design and operation. The combination of DNS caching and recursive functions in a name server is not mandatory; the functions can be implemented independently in servers for special purposes. Internet service providers typically provide recursive and caching name servers for their customers. In addition, many home networking routers implement DNS caches and recursion to improve efficiency in
5472-401: The class derived, the network identification was based on octet boundary segments of the entire address. Each class used successively additional octets in the network identifier, thus reducing the possible number of hosts in the higher order classes ( B and C ). The following table gives an overview of this now-obsolete system. Classful network design served its purpose in the startup stage of
5568-509: The client, in which case the real originating IP address is masked from the server receiving a request. A common practice is to have a NAT mask many devices in a private network. Only the public interface(s) of the NAT needs to have an Internet-routable address. The NAT device maps different IP addresses on the private network to different TCP or UDP port numbers on the public network. In residential networks, NAT functions are usually implemented in
5664-475: The computer. Computers at educational institutions would have the domain edu , for example. She and her team managed the Host Naming Registry from 1972 to 1989. By the early 1980s, maintaining a single, centralized host table had become slow and unwieldy and the emerging network required an automated naming system to address technical and personnel issues. Postel directed the task of forging
5760-505: The default configuration parameters of some network software and hardware components (e.g. netmask), and in the technical jargon used in network administrators' discussions. Early network design, when global end-to-end connectivity was envisioned for communications with all Internet hosts, intended that IP addresses be globally unique. However, it was found that this was not always necessary as private networks developed and public address space needed to be conserved. Computers not connected to
5856-438: The delegation for example.org. The glue records are address records that provide IP addresses for ns1.example.org. The resolver uses one or more of these IP addresses to query one of the domain's authoritative servers, which allows it to complete the DNS query. A common approach to reduce the burden on DNS servers is to cache the results of name resolution locally or on intermediary resolver hosts. Each DNS query result comes with
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#17327809654455952-488: The destination host. Two versions of the Internet Protocol are in common use on the Internet today. The original version of the Internet Protocol that was first deployed in 1983 in the ARPANET , the predecessor of the Internet, is Internet Protocol version 4 (IPv4). By the early 1990s, the rapid exhaustion of IPv4 address space available for assignment to Internet service providers and end-user organizations prompted
6048-452: The devices involved in the conflict is the default gateway access beyond the LAN for all devices on the LAN, all devices may be impaired. IP addresses are classified into several classes of operational characteristics: unicast, multicast, anycast and broadcast addressing. The most common concept of an IP address is in unicast addressing, available in both IPv4 and IPv6. It normally refers to
6144-502: The existing networks already designated by a network number. In 1981, the addressing specification was revised with the introduction of classful network architecture. Classful network design allowed for a larger number of individual network assignments and fine-grained subnetwork design. The first three bits of the most significant octet of an IP address were defined as the class of the address. Three classes ( A , B , and C ) were defined for universal unicast addressing. Depending on
6240-754: The first Unix name server implementation for the Berkeley Internet Name Domain, commonly referred to as BIND . In 1985, Kevin Dunlap of DEC substantially revised the DNS implementation. Mike Karels , Phil Almquist, and Paul Vixie then took over BIND maintenance. Internet Systems Consortium was founded in 1994 by Rick Adams , Paul Vixie , and Carl Malamud , expressly to provide a home for BIND development and maintenance. BIND versions from 4.9.3 onward were developed and maintained by ISC, with support provided by ISC's sponsors. As co-architects/programmers, Bob Halley and Paul Vixie released
6336-456: The first production-ready version of BIND version 8 in May 1997. Since 2000, over 43 different core developers have worked on BIND. In November 1987, RFC 1034 and RFC 1035 superseded the 1983 DNS specifications. Several additional Request for Comments have proposed extensions to the core DNS protocols. The domain name space consists of a tree data structure . Each node or leaf in the tree has
6432-544: The foreseeable future. The intent of the new design was not to provide just a sufficient quantity of addresses, but also redesign routing in the Internet by allowing more efficient aggregation of subnetwork routing prefixes. This resulted in slower growth of routing tables in routers. The smallest possible individual allocation is a subnet for 2 hosts, which is the square of the size of the entire IPv4 Internet. At these levels, actual address utilization ratios will be small on any IPv6 network segment. The new design also provides
6528-452: The global Internet. In a home situation, a public IP address is the IP address assigned to the home's network by the ISP . In this case, it is also locally visible by logging into the router configuration. Most public IP addresses change, and relatively often. Any type of IP address that changes is called a dynamic IP address. In home networks, the ISP usually assigns a dynamic IP. If an ISP gave
6624-412: The host, or more specifically, its network interface , and it provides the location of the host in the network, and thus, the capability of establishing a path to that host. Its role has been characterized as follows: "A name indicates what we seek. An address indicates where it is. A route indicates how to get there." The header of each IP packet contains the IP address of the sending host and that of
6720-504: The internet grew, leading to IPv4 address exhaustion over the 2010s. Its designated successor, IPv6 , uses 128 bits for the IP address, giving it a larger address space . Although IPv6 deployment has been ongoing since the mid-2000s, both IPv4 and IPv6 are still used side-by-side as of 2024. IPv4 addresses are usually displayed in a human-readable notation, but systems may use them in various different computer number formats . CIDR notation can also be used to designate how much of
6816-433: The length is only allowed to take 6 bits. The null label of length zero is reserved for the root zone. The full domain name may not exceed the length of 253 characters in its textual representation (or 254 with the trailing dot). In the internal binary representation of the DNS this maximum length of 253 requires 255 octets of storage, as it also stores the length of the first of many labels and adds last null byte. 255 length
6912-422: The local network. The client side of the DNS is called a DNS resolver. A resolver is responsible for initiating and sequencing the queries that ultimately lead to a full resolution (translation) of the resource sought, e.g., translation of a domain name into an IP address. DNS resolvers are classified by a variety of query methods, such as recursive , non-recursive , and iterative . A resolution process may use
7008-411: The multicast group address and the intermediary routers take care of making copies and sending them to all interested receivers (those that have joined the corresponding multicast group). Like broadcast and multicast, anycast is a one-to-many routing topology. However, the data stream is not transmitted to all receivers, just the one which the router decides is closest in the network. Anycast addressing
7104-408: The name server and IP address. For example, if the authoritative name server for example.org is ns1.example.org, a computer trying to resolve www.example.org first resolves ns1.example.org. As ns1 is contained in example.org, this requires resolving example.org first, which presents a circular dependency. To break the dependency, the name server for the top level domain org includes glue along with
7200-409: The name server providing the delegation must also provide one or more IP addresses for the authoritative name server mentioned in the delegation. This information is called glue . The delegating name server provides this glue in the form of records in the additional section of the DNS response, and provides the delegation in the authority section of the response. A glue record is a combination of
7296-509: The network and subnet. An IPv4 address has a size of 32 bits, which limits the address space to 4 294 967 296 (2 ) addresses. Of this number, some addresses are reserved for special purposes such as private networks (≈18 million addresses) and multicast addressing (≈270 million addresses). IPv4 addresses are usually represented in dot-decimal notation , consisting of four decimal numbers, each ranging from 0 to 255, separated by dots, e.g., 192.0.2.1 . Each part represents
7392-470: The network. NRS " second-level domains " consisted of UK.AC (JANET academic and scientific sites), UK.CO (commercial) and UK.MOD ( Ministry of Defence ). Any organisations not falling into these categories were given their own "second-level" name, e.g. UK.BL ( British Library ) or UK.NEL ( National Engineering Laboratory ). All NRS names had both a standard (long) and abbreviated (up to 18 characters) form. For example, UK.AC.CAMBRIDGE
7488-570: The networks and creating the Internet: Commercialization, privatization, broader access leads to the modern Internet: Examples of Internet services: The Domain Name System ( DNS ) is a hierarchical and distributed name service that provides a naming system for computers , services, and other resources on the Internet or other Internet Protocol (IP) networks. It associates various information with domain names ( identification strings ) assigned to each of
7584-593: The opportunity to separate the addressing infrastructure of a network segment, i.e. the local administration of the segment's available space, from the addressing prefix used to route traffic to and from external networks. IPv6 has facilities that automatically change the routing prefix of entire networks, should the global connectivity or the routing policy change, without requiring internal redesign or manual renumbering. The large number of IPv6 addresses allows large blocks to be assigned for specific purposes and, where appropriate, to be aggregated for efficient routing. With
7680-446: The poorly defined addressing policy created ambiguities for routing. This address type was abandoned and must not be used in new systems. Addresses starting with fe80:: , called link-local addresses , are assigned to interfaces for communication on the attached link. The addresses are automatically generated by the operating system for each network interface. This provides instant and automatic communication between all IPv6 hosts on
7776-547: The primary file by contacting the SRI Network Information Center (NIC), directed by Feinler, via telephone during business hours. Later, Feinler set up a WHOIS directory on a server in the NIC for retrieval of information about resources, contacts, and entities. She and her team developed the concept of domains. Feinler suggested that domains should be based on the location of the physical address of
7872-402: The query completely by querying other name servers as needed. In typical operation, a client issues a recursive query to a caching recursive DNS server, which subsequently issues non-recursive queries to determine the answer and send a single answer back to the client. The resolver, or another DNS server acting recursively on behalf of the resolver, negotiates use of recursive service using bits in
7968-404: The query headers. DNS servers are not required to support recursive queries. The iterative query procedure is a process in which a DNS resolver queries a chain of one or more DNS servers. Each server refers the client to the next server in the chain, until the current server can fully resolve the request. For example, a possible resolution of www.example.com would query a global root server, then
8064-423: The registry's RDAP and WHOIS services. That data can be used to gain insight on, and track responsibility for, a given host on the Internet. Using a simpler, more memorable name in place of a host's numerical address dates back to the ARPANET era. The Stanford Research Institute (now SRI International ) maintained a text file named HOSTS.TXT that mapped host names to the numerical addresses of computers on
8160-409: The reserved blocks. Typically, a network administrator will divide a block into subnets; for example, many home routers automatically use a default address range of 192.168.0.0 through 192.168.0.255 ( 192.168.0.0 / 24 ). In IPv6, the address size was increased from 32 bits in IPv4 to 128 bits, thus providing up to 2 (approximately 3.403 × 10 ) addresses. This is deemed sufficient for
8256-516: The root servers, and as a result, root name servers actually are involved in only a relatively small fraction of all requests. In theory, authoritative name servers are sufficient for the operation of the Internet. However, with only authoritative name servers operating, every DNS query must start with recursive queries at the root zone of the Domain Name System and each user system would have to implement resolver software capable of recursive operation. To improve efficiency, reduce DNS traffic across
8352-405: The same IP address to a host, based on its MAC address , each time it joins the network. A network administrator may configure DHCP by allocating specific IP addresses based on MAC address. DHCP is not the only technology used to assign IP addresses dynamically. Bootstrap Protocol is a similar protocol and predecessor to DHCP. Dialup and some broadband networks use dynamic address features of
8448-629: The separate classes can be thought of as an array of parallel namespace trees. Administrative responsibility for any zone may be divided by creating additional zones. Authority over the new zone is said to be delegated to a designated name server. The parent zone ceases to be authoritative for the new zone. The definitive descriptions of the rules for forming domain names appear in RFC 1035, RFC 1123, RFC 2181, and RFC 5892. A domain name consists of one or more parts, technically called labels , that are conventionally concatenated , and delimited by dots, such as example.com. The right-most label conveys
8544-423: The servers referred to, and iteratively repeats this process until it receives an authoritative answer. The diagram illustrates this process for the host that is named by the fully qualified domain name "www.wikipedia.org". This mechanism would place a large traffic burden on the root servers, if every resolution on the Internet required starting at the root. In practice caching is used in DNS servers to off-load
8640-457: The source or destination of packets traversing the Internet. When the link-local IPv4 address block was reserved, no standards existed for mechanisms of address autoconfiguration. Filling the void, Microsoft developed a protocol called Automatic Private IP Addressing (APIPA), whose first public implementation appeared in Windows 98 . APIPA has been deployed on millions of machines and became
8736-420: The specially defined all-nodes multicast address. A multicast address is associated with a group of interested receivers. In IPv4, addresses 224.0.0.0 through 239.255.255.255 (the former Class D addresses) are designated as multicast addresses. IPv6 uses the address block with the prefix ff00:: / 8 for multicast. In either case, the sender sends a single datagram from its unicast address to
8832-604: The use of the Transmission Control Protocol (TCP) as well as numerous other protocol developments. An often-used analogy to explain the DNS is that it serves as the phone book for the Internet by translating human-friendly computer hostnames into IP addresses. For example, the hostname www.example.com within the domain name example.com translates to the addresses 93.184.216.34 ( IPv4 ) and 2606:2800:220:1:248:1893:25c8:1946 ( IPv6 ). The DNS can be quickly and transparently updated, allowing
8928-547: Was caused when the least significant part of an Internet address matched the most significant part of an NRS address and vice versa. The ccTLD " .cs " for Czechoslovakia came into use around 1990-2 until 1995. The classic joke was that e-mail intended for UK universities ended up in Czechoslovakia, since many JANET e-mail addresses were of the form user@UK.AC. universityname .CS , where "CS" stood for Computer Science (department). Another significant difference from
9024-467: Was designed to avoid a single large central database. In addition, the DNS specifies the technical functionality of the database service that is at its core. It defines the DNS protocol, a detailed specification of the data structures and data communication exchanges used in the DNS, as part of the Internet protocol suite . The Internet maintains two principal namespaces , the domain name hierarchy and
9120-622: Was never referred to as IPv5. Other versions v1 to v9 were defined, but only v4 and v6 ever gained widespread use. v1 and v2 were names for TCP protocols in 1974 and 1977, as there was no separate IP specification at the time. v3 was defined in 1978, and v3.1 is the first version where TCP is separated from IP. v6 is a synthesis of several suggested versions, v6 Simple Internet Protocol , v7 TP/IX: The Next Internet , v8 PIP — The P Internet Protocol , and v9 TUBA — Tcp & Udp with Big Addresses . IP networks may be divided into subnetworks in both IPv4 and IPv6 . For this purpose, an IP address
9216-437: Was the less widely used standard equivalent of the abbreviated name UK.AC.CAM . For email, interoperability between the " Grey Book " email addressing style of user@UK.AC.SITE and ARPA and USENET addresses of the style user@site.ac.uk was achieved by way of mail gateway at University College London . As Internet usage expanded and commercial entities emerged, the more general Domain Name System (DNS) superseded
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