system to identify resources on a net
Reading: Domain Name System – Flickroom
The Domain Name System ( DNS ) is the hierarchical and decentralized name system used to identify computers, services, and early resources approachable through the Internet or early Internet Protocol ( IP ) networks. The resource records contained in the DNS associate domain names with other forms of data. These are most normally used to map human-friendly world names to the numeric IP addresses computers need to locate services and devices using the underlie network protocols, but have been extended over time to perform many early functions as well. The Domain Name System has been an substantive part of the functionality of the Internet since 1985 .
- 1 affair
- 2 history
- 3 structure
- 4 operation
- 5 DNS message format
- 6 DNS enchant protocols
- 7 resource records
- 8 Protocol extensions
- 9 security system issues
- 10 privacy and tracking issues
- 11 Domain name registration
- 12 RFC documents
- 13 See besides
- 14 References
An often-used analogy to explain the Domain Name System is that it serves as the telephone reserve for the Internet by translating human-friendly calculator hostnames into IP addresses. For exercise, the knowledge domain name www.example.com translates to the addresses 126.96.36.199 ( IPv4 ) and 2606:2800:220:1:248:1893:25c8:1946 ( IPv6 ). The DNS can be cursorily and transparently updated, allowing a serve ‘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 electronic mail addresses without having to know how the computer actually locates the services. An important and omnipresent function of the DNS is its central character in circulate Internet services such as cloud services and content pitch networks. [ 2 ] When a user accesses a distribute Internet serve using a URL, the sphere name of the URL is translated to the IP address of a waiter that is proximal to the drug user. The key functionality of the DNS exploited here is that different users can simultaneously get different translations for the same sphere name, a key detail of divergence from a traditional phone-book view of the DNS. This work of using the DNS to assign proximal servers to users is samara to providing faster and more reliable responses on the Internet and is wide used by most major Internet services. [ 3 ] The DNS reflects the structure of administrative responsibility in the Internet. [ 4 ] Each subdomain is a partition of administrative autonomy delegated to a director. For zones operated by a register, administrative information is frequently complemented by the register ‘s RDAP and WHOIS services. That data can be used to gain penetration on, and racetrack responsibility for, a given host on the Internet. [ 5 ]
Using a simple, more memorable diagnose in place of a host ‘s numeral address dates back to the ARPANET earned run average. 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 the ARPANET. [ 6 ] [ 7 ] Elizabeth Feinler developed and maintained the first ARPANET directory. care of numeral 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. [ 10 ] Addresses were assigned manually. Computers, including their hostnames and addresses, were added to the primary charge by contacting the SRI Network Information Center ( NIC ), directed by Feinler, call during business hours. [ 11 ] 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 localization of the physical address of the computer. Computers at educational institutions would have the world edu, for example. She and her team managed the Host Naming Registry from 1972 to 1989. [ 15 ] By the early 1980s, maintaining a single, centralize host table had become slow and unwieldy and the emerging network required an automated name system to address technical and personnel issues. Postel directed the undertaking of forging a compromise between five competing proposals of solutions to Paul Mockapetris. Mockapetris rather created the Domain Name System in 1983. [ 11 ] [ 16 ] The Internet Engineering Task Force published the original specifications in RFC 882 and RFC 883 in November 1983. [ 17 ] [ 18 ] In 1984, four Flickroom students, Douglas Terry, Mark Painter, David Riggle, and Songnian Zhou, wrote the first Unix name server execution for the Berkeley Internet Name Domain, normally referred to as BIND. [ 19 ] In 1985, Kevin Dunlap of DEC well revised the DNS execution. Mike Karels, Phil Almquist, and Paul Vixie have maintained BIND since then. [ 20 ] In the early 1990s, BIND was ported to the Windows NT platform. In November 1987, RFC 1034 [ 21 ] and RFC 1035 [ 4 ] superseded the 1983 DNS specifications. respective extra Request for Comments have proposed extensions to the kernel DNS protocols. [ 22 ]
Domain list outer space
The domain name space consists of a tree data structure. Each node or leaf in the tree has a label and zero or more resource records ( RR ), which hold information associated with the domain name. The world name itself consists of the pronounce, concatenated with the name of its parent node on the correct, separated by a point. [ 23 ] The tree sub-divides into zones begin at the beginning zone. A DNS zone may consist of merely one knowledge domain, or may consist of many domains and sub-domains, depending on the administrative choices of the zone director. DNS can besides be partitioned according to class where the classify classes can be thought of as an array of parallel namespace trees. [ 24 ]
Internet, organized into zones, each served by a name server The hierarchical Domain Name System for class, organized into zones, each served by a diagnose server administrative province for any zone may be divided by creating extra zones. authority over the new zone is said to be delegated to a designated name server. The rear partition ceases to be authoritative for the new zone. [ 24 ]
Domain name syntax, internationalization
The definitive descriptions of the rules for forming sphere 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 the top-level knowledge domain ; for model, the knowledge 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 branch, or subdomain of the domain to the right. For example, the label example specifies a subdomain of the com knowledge domain, and www is a subdomain of example.com. This tree of subdivisions may have up to 127 levels. [ 25 ] A label may contain zero to 63 characters. The nothing label, of distance nothing, is reserved for the ancestor zone. The wax knowledge domain name may not exceed the length of 253 characters in its textual representation. [ 21 ] In the home binary representation of the DNS the utmost distance requires 255 octets of storehouse, as it besides stores the distance of the name. [ 4 ] Although no technical limit exists to prevent domain name labels using any character which is representable by an octet, hostnames use a prefer format and character laid. 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 hyphenate. This predominate is known as the LDH rule ( letters, digits, hyphenate ). Domain names are interpreted in case-independent manner. [ 26 ] Labels may not start or end with a hyphen. [ 27 ] An extra rule requires that top-level domain names should not be all-numeric. [ 27 ] The circumscribed jell 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 the Internationalizing Domain Names in Applications ( IDNA ) system, by which exploiter applications, such as web browsers, map Unicode strings into the valid DNS fictional character set using Punycode. In 2009 ICANN approved the installation of internationalize sphere mention country code top-level domains ( ccTLD mho ). In summation, many registries of the existing top-level knowledge domain names ( TLD s ) have adopted the IDNA system, guided by RFC 5890, RFC 5891, RFC 5892, RFC 5893 .
The Domain Name System is maintained by a distribute database system, which uses the client–server model. The nodes of this database are the name servers. Each sphere has at least one authoritative DNS server that publishes information about that world and the name servers of any domains subordinate to it. The top of the hierarchy is served by the root list servers, the servers to query when looking up ( resolving ) a TLD .
An authoritative name server is a name server that entirely gives answers to DNS queries from data that has been configured by an master beginning, for case, the domain administrator or by active DNS methods, in contrast to answers obtained via a question to another appoint server that merely maintains a cache of data. An authoritative identify server can either be a primary server or a secondary waiter. Historically the terms master/slave and primary/secondary were sometimes used interchangeably [ 28 ] 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 update mechanism in the DNS protocol in communication with its elementary to maintain an identical copy of the elementary records. Every DNS zone must be assigned a jell of authoritative name servers. This set of servers is stored in the rear domain zone with name server ( NS ) records. An authoritative waiter indicates its condition of supplying authoritative answers, deemed authoritative, by setting a protocol flag, called the “ Authoritative Answer “ ( AA ) spot in its responses. [ 4 ] This flag is normally reproduced prominently in the output signal of DNS administration question tools, such as dig, to indicate that the responding name server is an authority for the domain name in question. [ 4 ] When a mention server is designated as the authoritative server for a knowledge domain name for which it does not have authoritative data, it presents a type of error called a “ square deputation ” or “ feeble response ”. [ 29 ] [ 30 ]
Address solution mechanism
Domain name resolvers determine the sphere name servers responsible for the world identify in question by a sequence of queries starting with the right-most ( top-level ) knowledge domain pronounce .
A DNS resolver that implements the iterative border on mandated by RFC 1034 ; in this case, the resolver consults three identify servers to resolve the amply qualify knowledge domain name “ www.wikipedia.org ”. For proper operation of its domain name resolver, a network host is configured with an initial hoard ( hints ) of the known addresses of the root list servers. The hints are updated sporadically by an administrator by retrieving a dataset from a authentic source. Assuming the resolver has no cached records to accelerate the process, the resolution process starts with a question to one of the etymon servers. In distinctive operation, the root servers do not answer directly, but respond with a referral to more authoritative servers, for example, a question for “ www.wikipedia.org ” is referred to the org servers. The resolver now queries the servers referred to, and iteratively repeats this work until it receives an authoritative answer. The diagram illustrates this process for the host that is named by the in full qualified domain list “ www.wikipedia.org ”. This mechanism would place a large traffic charge on the root servers, if every settlement on the Internet required starting at the solution. In commit hoard is used in DNS servers to off-load the root servers, and as a resultant role, etymon name servers actually are involved in lone a relatively little fraction of all requests .
recursive and caching appoint server
In theory, authoritative name servers are sufficient for the operation of the Internet. however, with entirely authoritative name servers operate, every DNS question must start with recursive queries at the settle zone of the Domain Name System and each drug user system would have to implement resolver software capable of recursive operation. To improve efficiency, reduce DNS traffic across the Internet, and increase performance in end-user applications, the Domain Name System supports DNS cache servers which store DNS question results for a menstruation of time determined in the shape ( time-to-live ) of the domain name read in wonder. typically, such caching DNS servers besides implement the recursive algorithm necessary to resolve a given name starting with the DNS settle through to the authoritative name servers of the question domain. With this serve implemented in the name server, user applications gain efficiency in design and operation. The combination of DNS hoard and recursive functions in a name server is not mandate ; the functions can be implemented independently in servers for particular purposes. Internet service providers typically provide recursive and caching mention servers for their customers. In addition, many home plate networking routers enforce DNS caches and recursion to improve efficiency in the local net .
The node side of the DNS is called a DNS resolver. A resolver is creditworthy for initiating and sequencing the queries that ultimately lead to a full moon solution ( translation ) of the resource sought, for example, transformation of a domain name into an IP address. DNS resolvers are classified by a kind of question methods, such as recursive, non-recursive, and iterative. A resolution process may use a combination of these methods. [ 21 ] 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 solution without querying early servers. In sheath of a caching DNS resolver, the non-recursive question of its local DNS cache delivers a resultant role and reduces the load on upriver DNS servers by caching DNS resource records for a period of time after an initial reaction from upstream DNS servers. In a recursive query, a DNS resolver queries a single DNS server, which may in turn question other DNS servers on behalf of the petitioner. For example, a bare stub resolver running on a home router typically makes a recursive question to the DNS server run by the exploiter ‘s ISP. A recursive question is one for which the DNS server answers the question completely by querying other list servers as needed. In typical operation, a customer issues a recursive question to a caching recursive DNS server, which subsequently issues non-recursive queries to determine the answer and send a individual answer back to the customer. The resolver, or another DNS server acting recursively on behalf of the resolver, negotiates use of recursive service using bits in the question headers. DNS servers are not required to support recursive queries. The iterative query procedure is a serve in which a DNS resolver queries a chain of one or more DNS servers. Each waiter refers the client to the following waiter in the chain, until the current server can amply resolve the request. For exercise, a possible resolution of www.example.com would query a ball-shaped root server, then a “ com ” server, and last an “ example.com ” server .
circular dependencies and glue records
name servers in delegations are identified by name, rather than by IP address. This means that a dissolve name server must issue another DNS request to find out the IP address of the waiter to which it has been referred. If the diagnose given in the delegating is a subdomain of the knowledge domain for which the delegating is being provided, there is a round colony. In this event, the name server providing the delegating must besides provide one or more information science addresses for the authoritative name waiter mentioned in the deputation. This information is called glue. The delegate identify waiter provides this glue in the mannequin of records in the additional section of the DNS reception, and provides the deputation in the authority section of the response. A glue record is a combination of the appoint waiter 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 dependence. To break the colony, the name waiter for the lead level sphere org includes glue along with the delegating 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 sphere ‘s authoritative servers, which allows it to complete the DNS question .
A standard practice in implementing name resolution in applications is to reduce the load on the Domain Name System servers by caching results locally, or in intercede resolver hosts. Results obtained from a DNS request are always associated with the time to live ( TTL ), an passing time after which the results must be discarded or refreshed. The TTL is set by the administrator of the authoritative DNS server. The period of robustness may vary from a few seconds to days or even weeks. As a resultant role of this distribute hoard computer architecture, changes to DNS records do not propagate throughout the network immediately, but require all caches to expire and to be refreshed after the TTL. RFC 1912 bring basic rules for determining appropriate TTL values. Some resolvers may override TTL values, as the protocol supports caching for up to sixty-eight years or no hoard at all. negative hoard, i.e. the hoard of the fact of non-existence of a phonograph record, is determined by identify servers authoritative for a zone which must include the Start of Authority ( SOA ) record when reporting no datum of the requested type exists. The value of the minimum field of the SOA record and the TTL of the SOA itself is used to establish the TTL for the negative answer .
A change by reversal DNS search is a question of the DNS for knowledge domain names when the IP address is known. multiple knowledge domain names may be associated with an IP address. The DNS stores IP addresses in the form of domain names as particularly formatted names in pointer ( PTR ) records within the infrastructure top-level domain arpa. For IPv4, the domain is in-addr.arpa. For IPv6, the overrule search domain is ip6.arpa. The IP address is represented as a name in reverse-ordered octet representation for IPv4, and reverse-ordered nibble representation for IPv6. When performing a invert search, the DNS customer converts the address into these formats before querying the identify for a PTR record following the deputation chain as for any DNS question. For exercise, assuming the IPv4 address 188.8.131.52 is assigned to Flickroommedia, it is represented as a DNS name in reversion club : 184.108.40.206.in-addr.arpa. When the DNS resolver gets a pointer ( PTR ) request, it begins by querying the etymon servers, which orient to the servers of american Registry for Internet Numbers ( ARIN ) for the 208.in-addr.arpa zone. ARIN ‘s servers delegate 152.80.208.in-addr.arpa to Flickroommedia to which the resolver sends another question for 220.127.116.11.in-addr.arpa, which results in an authoritative answer .
DNS resolution succession Users broadly do not communicate directly with a DNS resolver. alternatively DNS solution takes place transparently in applications such as vane browsers, electronic mail clients, and other Internet applications. When an application makes a request that requires a domain diagnose search, such programs send a resoluteness request to the DNS resolver in the local operate system, which in turn handles the communications required. The DNS resolver will about constantly have a hoard ( see above ) containing late lookups. If the cache can provide the answer to the request, the resolver will return the rate in the hoard to the program that made the request. If the hoard does not contain the answer, the resolver will send the request to one or more designate DNS servers. In the character of most home plate users, the Internet service provider to which the machine connects will normally supply this DNS server : such a user will either have configured that server ‘s address manually or allowed DHCP to set it ; however, where systems administrators have configured systems to use their own DNS servers, their DNS resolvers point to individually maintained name servers of the administration. In any event, the name server frankincense queried will follow the action outlined above, until it either successfully finds a resultant role or does not. It then returns its results to the DNS resolver ; assuming it has found a result, the resolver punctually caches that result for future use, and hands the result back to the software which initiated the request .
Some large ISPs have configured their DNS servers to violate rules, such as by disobeying TTLs, or by indicating that a world mention does not exist precisely because one of its diagnose servers does not respond. [ 31 ] Some applications such as vane browsers maintain an inner DNS hoard to avoid perennial lookups via the network. This drill can add extra trouble when debugging DNS issues as it obscures the history of such data. These caches typically use very inadequate caching times on the order of one hour. [ 32 ]
Internet Explorer represents a luminary exception : versions up to IE 3.x cache DNS records for 24 hours by nonpayment. Internet Explorer 4.x and subsequently versions ( up to IE 8 ) decrease the default option timeout value to half an hour, which may be changed by modifying the default shape. [ 33 ] When Google Chrome detects issues with the DNS server it displays a specific error message .
The Domain Name System includes respective other functions and features. Hostnames and IP addresses are not required to match in a one-to-one kinship. Multiple hostnames may correspond to a individual IP address, which is utilitarian in virtual host, in which many web sites are served from a unmarried server. alternatively, a single hostname may resolve to many IP addresses to facilitate fault permissiveness and warhead distribution to multiple server instances across an enterprise or the ball-shaped Internet. DNS serves other purposes in addition to translating names to IP addresses. For exemplify, mail transfer agents use DNS to find the best chain mail waiter to deliver electronic mail : An MX record provides a map between a domain and a mail exchanger ; this can provide an extra layer of fault tolerance and warhead distribution. The DNS is used for effective memory and distribution of IP addresses of blacklist electronic mail hosts. A common method acting is to place the IP savoir-faire of the capable host into the sub-domain of a higher level domain diagnose, and to resolve that name to a record that indicates a positive or a negative indication. For exemplar :
- The address 18.104.22.168 is blacklisted. It points to 22.214.171.124.blacklist.example, which resolves to 127.0.0.1.
- The address 126.96.36.199 is not blacklisted and points to 188.8.131.52.blacklist.example. This hostname is either not configured, or resolves to 127.0.0.2.
e-mail servers can query blacklist.example to find out if a specific host associate to them is in the blacklist. many of such blacklists, either subscription-based or free of monetary value, are available for function by electronic mail administrators and anti-spam software. To provide resilience in the event of computer or network failure, multiple DNS servers are normally provided for coverage of each world. At the top level of ball-shaped DNS, thirteen groups of ancestor name servers exist, with extra “ copies ” of them distributed global via anycast address. Dynamic DNS ( DDNS ) updates a DNS server with a client IP address on-the-fly, for example, when moving between ISPs or mobile hot spots, or when the IP address changes administratively .
DNS message format
The DNS protocol uses two types of DNS messages, queries and replies ; both have the same format. Each message consists of a header and four sections : interrogate, answer, assurance, and an extra space. A header field ( flags ) controls the capacity of these four sections. [ 21 ] The header section consists of the follow fields : Identification, Flags, Number of questions, Number of answers, Number of authority resource records ( RRs ), and Number of additional RRs. Each field is 16 bits long, and appears in the order given. The recognition plain is used to match responses with queries. The flag field consists of sub-fields as follows :
|QR||Indicates if the message is a query (0) or a reply (1)||1|
|OPCODE||The type can be QUERY (standard query, 0), IQUERY (inverse query, 1), or STATUS (server status request, 2)||4|
|AA||Authoritative Answer, in a response, indicates if the DNS server is authoritative for the queried hostname||1|
|TC||TrunCation, indicates that this message was truncated due to excessive length||1|
|RD||Recursion Desired, indicates if the client means a recursive query||1|
|RA||Recursion Available, in a response, indicates if the replying DNS server supports recursion||1|
|Z||Zero, reserved for future use||3|
|RCODE||Response code, can be NOERROR (0), FORMERR (1, Format error), SERVFAIL (2), NXDOMAIN (3, Nonexistent domain), etc.||4|
After the masthead, the header ends with four 16-bit integers which contain the number of records in each of the sections that follow, in the same order .
The interrogate section has a bare format than the resource record format used in the other sections. Each question record ( there is normally good one in the section ) contains the follow fields :
|NAME||Name of the requested resource||Variable|
|TYPE||Type of RR (A, AAAA, MX, TXT, etc.)||2|
The knowledge domain appoint is broken into discrete labels which are concatenated ; each label is prefixed by the length of that label. [ 35 ]
DNS enchant protocols
DNS-over-UDP/53 ( “ Do53 ” )
From the time of its origin in 1983 until quite recently, DNS has chiefly answered queries on User Datagram Protocol ( UDP ) port total 53. [ 4 ] such queries consist of a clear-text request sent in a individual UDP packet from the customer, responded to with a clear-text reply sent in a individual UDP packet from the waiter. When the duration of the answer exceeds 512 bytes and both client and server support Extension Mechanisms for DNS ( EDNS ), larger UDP packets may be used. [ 37 ] Use of DNS-over-UDP is limited by, among other things, its miss of transport-layer encoding, authentication, reliable delivery, and message length .
DNS-over-TCP/53 ( “ Do53/TCP ” )
In 1989, RFC 1123 specified optional Transmission Control Protocol ( TCP ) transport for DNS queries, replies and, particularly, zone transfers. Via fragmentation of long replies, TCP allows longer responses, dependable manner of speaking, and re-use of durable connections between clients and servers .
The DNSCrypt protocol, which was developed in 2011 outside the IETF standards model, introduced DNS encoding on the downriver english of recursive resolvers, wherein clients code question payloads using servers ‘ populace keys, which are published in the DNS ( rather than relying upon third-party security authorities ) and which may in turn be protected by DNSSEC signatures. [ 38 ] DNSCrypt uses either TCP or UDP port 443, the lapp port as HTTPS encrypted web traffic. This introduced not entirely privacy regarding the message of the question, but besides a meaning measure of firewall-traversal capability. In 2019, DNSCrypt was further extended to support an “ anonymized ” mode, alike to the proposed “ oblivious DNS, ” in which an entrance node receives a question which has been encrypted with the public key of a different waiter, and relays it to that waiter, which acts as an issue node, performing the recursive resolution. [ 39 ] Privacy of user/query pair is created, since the entrance node does not know the contentedness of the question, while the egress nodes does not know the identity of the customer. DNSCrypt was first implemented in production by OpenDNS in December of 2011 .
DNS-over-TLS ( “ DoT ” )
An IETF standard for code DNS emerged in 2016, utilizing standard Transport Layer Security ( TLS ) to protect the entire connection, preferably than good the DNS cargo. DoT servers listen on TCP port 853. RFC7858 specifies that opportunist encoding and authenticate encoding may be supported, but did not make either server or customer authentication compulsory .
DNS-over-HTTPS ( “ DoH ” )
A competing standard for DNS question conveyance was introduced in 2018, tunneling DNS question datum over HTTPS ( which in change by reversal transports HTTP over TLS ). DoH was promoted as a more web-friendly alternative to DNS since, like DNSCrypt, it travels on TCP port 443, and frankincense looks exchangeable to web traffic, though they are easily differentiable in practice. [ 40 ] DoH has been widely criticized for decreasing user anonymity relative to DoT. [ 41 ]
Like other Internet protocols, DNS may be run over VPNs and tunnels. One use which has become common adequate since 2019 to warrant its own frequently used acronym is DNS-over- Tor. The privacy gains of forgetful DNS can be garnered through the use of the preexistent Tor network of entrance and egress nodes, paired with the transport-layer encoding provided by TLS. [ 42 ]
forgetful DNS-over-HTTPS ( “ ODoH ” )
In 2021, an “ forgetful ” execution of DoH was proposed and has been implemented in draft kind, combining ingress/egress separation with HTTPS tunneling and TLS transport-layer encoding in a unmarried defined protocol. [ 43 ]
The Domain Name System specifies a database of information elements for network resources. The types of information elements are categorized and organized with a list of DNS record types, the resource records ( RRs ). Each phonograph record has a type ( identify and act ), an exhalation time ( time to live ), a class, and type-specific data. Resource records of the lapp type are described as a resource record set ( RRset ), having no especial regulate. DNS resolvers return the entire hardened upon question, but servers may implement round-robin ordering to achieve load balancing. In line, the Domain Name System Security Extensions ( DNSSEC ) study on the complete laid of resource record in canonic rate. When sent over an Internet Protocol network, all records use the coarse format specified in RFC 1035 : [ 44 ]
|NAME||Name of the node to which this record pertains||Variable|
|TYPE||Type of RR in numeric form (e.g., 15 for MX RRs)||2|
|TTL||Count of seconds that the RR stays valid (The maximum is 231−1, which is about 68 years)||4|
|RDLENGTH||Length of RDATA field (specified in octets)||2|
|RDATA||Additional RR-specific data||Variable, as per RDLENGTH|
NAME is the amply stipulate world name of the node in the tree [ clarification needed ]. On the electrify, the diagnose may be shortened using label compression where ends of knowledge domain names mentioned earlier in the packet can be substituted for the end of the current domain name. TYPE is the record type. It indicates the format of the data and it gives a hint of its intended manipulation. For exercise, the A record is used to translate from a domain name to an IPv4 address, the NS record lists which name servers can answer lookups on a DNS zone, and the MX record specifies the mail server used to handle mail for a domain specified in an e-mail address. RDATA is data of type-specific relevance, such as the IP address for address records, or the priority and hostname for MX records. Well known record types may use label compression in the RDATA field, but “ strange ” record types must not ( RFC 3597 ). The CLASS of a criminal record is set to IN ( for Internet ) for coarse DNS records involving Internet hostnames, servers, or IP addresses. In accession, the classes Chaos ( CH ) and Hesiod ( HS ) exist. [ 45 ] Each class is an independent name space with potentially different delegations of DNS zones. In summation to resource records defined in a zone file, the domain name system besides defines respective request types that are used only in communication with other DNS nodes ( on the wire ), such as when performing zone transfers ( AXFR/IXFR ) or for EDNS ( OPT ) .
Wildcard DNS records
The world appoint system supports wildcard DNS records which specify names that start with the asterisk label, ‘* ‘, e.g., *.example. [ 21 ] [ 46 ] DNS records belonging to wildcard domain names specify rules for generating resource records within a single DNS partition by substituting unharmed labels with match components of the question name, including any specify descendants. For exercise, in the adopt shape, the DNS zone x.example specifies that all subdomains, including subdomains of subdomains, of x.example use the mail exchanger ( MX ) a.x.example. The A read for a.x.example is needed to specify the mail exchanger IP address. As this has the result of excluding this domain diagnose and its subdomains from the wildcard matches, an extra MX criminal record for the subdomain a.x.example, a well as a wildcarded MX record for all of its subdomains, must besides be defined in the DNS zone .
x.example. MX 10 a.x.example. *.x.example. MX 10 a.x.example. *.a.x.example. MX 10 a.x.example. a.x.example. MX 10 a.x.example. a.x.example. AAAA 2001:db8::1
The function of wildcard records was refined in RFC 4592, because the original definition in RFC 1034 was incomplete and resulted in misinterpretations by implementers. [ 46 ]
The original DNS protocol had limited provisions for extension with newly features. In 1999, Paul Vixie published in RFC 2671 ( superseded by RFC 6891 ) an extension mechanism, called annex Mechanisms for DNS ( EDNS ) that introduced optional protocol elements without increasing overhead when not in use. This was accomplished through the OPT pseudo-resource record that only exists in cable transmissions of the protocol, but not in any zone files. initial extensions were besides suggested ( EDNS0 ), such as increasing the DNS message size in UDP datagrams .
Dynamic DNS updates use the UPDATE DNS opcode to add or remove resource records dynamically from a zone database maintained on an authoritative DNS waiter. The feature is described in RFC 2136. This facility is useful to register network clients into the DNS when they boot or become otherwise available on the network. As a boot customer may be assigned a different IP address each time from a DHCP server, it is not possible to provide static DNS assignments for such clients .
security system issues
primitively, security concerns were not major invention considerations for DNS software or any software for deployment on the early on Internet, as the network was not receptive for engagement by the general public. however, the expansion of the Internet into the commercial sector in the 1990s changed the requirements for security measures to protect data integrity and user authentication. respective vulnerability issues were discovered and exploited by malicious users. One such consequence is DNS cache poison, in which data is distributed to caching resolvers under the pretense of being an authoritative lineage server, thereby polluting the data store with potentially fake information and farseeing passing times ( time-to-live ). subsequently, legitimate lotion requests may be redirected to network hosts operated with malicious purpose. DNS responses traditionally do not have a cryptanalytic signature, leading to many attack possibilities ; the Domain Name System Security Extensions ( DNSSEC ) modify DNS to add support for cryptographically signed responses. DNSCurve has been proposed as an alternative to DNSSEC. other extensions, such as TSIG, add support for cryptanalytic authentication between trusted peers and are normally used to authorize zone transfer or dynamic update operations. Some domain names may be used to achieve spoofing effects. For model, paypal.com and paypa1.com are different names, yet users may be ineffective to distinguish them in a graphic drug user interface depending on the drug user ‘s chosen font. In many fonts the letter l and the numeral 1 look identical similar or even identical. This problem is acute in systems that support internationalized knowledge domain names, as many character codes in ISO 10646 may appear identical on distinctive calculator screens. This vulnerability is occasionally exploited in phishing. [ 47 ] Techniques such as forward-confirmed reverse DNS can besides be used to help validate DNS results. DNS can besides “ leak ” from otherwise secure or secret connections, if attention is not paid to their configuration, and at times DNS has been used to bypass firewalls by malicious persons, and exfiltrate data, since it is much seen as innocuous .
privacy and tracking issues
primitively designed as a populace, hierarchical, distributed and heavily hoard database, DNS protocol has no confidentiality controls. User queries and nameserver responses are being sent unencrypted which enables network mailboat sniff, DNS highjacking, DNS hoard poisoning and man-in-the-middle attacks. This lack is normally used by cybercriminals and network operators for market purposes, exploiter authentication on captive portals and censoring. [ 48 ] User privacy is further exposed by proposals for increasing the level of client IP information in DNS queries ( RFC 7871 ) for the benefit of subject Delivery Networks. The main approaches that are in practice to counter privacy issues with DNS :
- VPNs, which move DNS resolution to the VPN operator and hide user traffic from local ISP,
- Tor, which replaces traditional DNS resolution with anonymous .onion domains, hiding both name resolution and user traffic behind onion routing counter-surveillance,
- Proxies and public DNS servers, which move the actual DNS resolution to a third-party provider, who usually promises little or no request logging and optional added features, such as DNS-level advertisement or pornography blocking.
- Public DNS servers can be queried using traditional DNS protocol, in which case they provide no protection from local surveillance, or DNS-over-HTTPS, DNS-over-TLS and DNSCrypt, which do provide such protection
Solutions preventing DNS inspection by local net operator are criticized for thwarting corporate network security system policies and Internet censoring. They are besides criticized from privacy target of position, as giving away the DNS resolution to the hands of a small number of companies known for monetizing drug user traffic and for centralizing DNS list solution, which is broadly perceived as harmful for the Internet. [ 48 ]
Google is the prevailing provider of the platform in Android, the browser in Chrome, and the DNS resolver in the 184.108.40.206 service. Would this scenario be a case of a individual bodied entity being in a position of overarching master of the entire namespace of the Internet ? Netflix already fielded an app that used its own DNS resolution mechanism mugwump of the chopine upon which the app was running. What if the Facebook app included DoH ? What if Apple ’ s iOS used a DoH-resolution mechanism to bypass local anesthetic DNS resolution and steer all DNS queries from Apple ’ s platforms to a set of Apple-operated appoint resolvers ? — DNS Privacy and the IETF
Domain name registration
The right to use a knowledge domain name is delegated by domain name registrars which are accredited by the Internet Corporation for Assigned Names and Numbers ( ICANN ) or other organizations such as OpenNIC, that are charged with overseeing the name and number systems of the Internet. In addition to ICANN, each top-level domain ( TLD ) is maintained and serviced technically by an administrative organization, operating a register. A registry is responsible for operating the database of names within its authoritative zone, although the term is most much used for TLDs. A registrant is a person or organization who asked for domain registration. [ 22 ] The register receives registration data from each world appoint registrar, which is authorized ( accredited ) to assign names in the comparable zone and publishes the information using the WHOIS protocol. As of 2015, usage of RDAP is being considered. [ 49 ] ICANN publishes the complete list of TLDs, TLD registries, and domain list registrars. registrant information associated with knowledge domain names is maintained in an on-line database accessible with the WHOIS serve. For most of the more than 290 country code top-level domains ( ccTLDs ), the domain registries maintain the WHOIS ( Registrant, name servers, exhalation dates, etc. ) data. For case, DENIC, Germany NIC, holds the DE domain data. From about 2001, most generic top-level domain ( gTLD ) registries have adopted this alleged thick register approach, i.e. keeping the WHOIS data in central registries alternatively of registrar databases. For top-level domains on COM and NET, a thin register model is used. The domain register ( for example, GoDaddy, BigRock and PDR, VeriSign, and so forth, etc. ) holds basic WHOIS data ( i, registrar and mention servers, and so forth ). Organizations, or registrants using ORG on the other pass, are on the public Interest Registry entirely. Some sphere identify registries, often called network information centers ( NIC ), besides function as registrars to end-users, in addition to providing access to the WHOIS datasets. The top-level world registries, such as for the domains COM, NET, and ORG use a registry-registrar model consisting of many knowledge domain name registrars. [ 50 ] In this method acting of management, the register entirely manages the domain mention database and the kinship with the registrars. The registrants ( users of a domain diagnose ) are customers of the registrar, in some cases through extra subcontract of resellers .
The Domain Name System is defined by Request for Comments ( RFC ) documents published by the Internet Engineering Task Force ( Internet standards ). The play along is a list of RFCs that define the DNS protocol .
- RFC 1034, Domain Names – Concepts and Facilities
- RFC 1035, Domain Names – Implementation and Specification
- RFC 1123, Requirements for Internet Hosts—Application and Support
- RFC 1995, Incremental Zone Transfer in DNS
- RFC 1996, A Mechanism for Prompt Notification of Zone Changes (DNS NOTIFY)
- RFC 2136, Dynamic Updates in the domain name system (DNS UPDATE)
- RFC 2181, Clarifications to the DNS Specification
- RFC 2308, Negative Caching of DNS Queries (DNS NCACHE)
- RFC 2672, Non-Terminal DNS Name Redirection
- RFC 2845, Secret Key Transaction Authentication for DNS (TSIG)
- RFC 3225, Indicating Resolver Support of DNSSEC
- RFC 3226, DNSSEC and IPv6 A6 aware server/resolver message size requirements
- RFC 3596, DNS Extensions to Support IP Version 6
- RFC 3597, Handling of Unknown DNS Resource Record (RR) Types
- RFC 4343, Domain Name System (DNS) Case Insensitivity Clarification
- RFC 4592, The Role of Wildcards in the Domain Name System
- RFC 4635, HMAC SHA TSIG Algorithm Identifiers
- RFC 5001, DNS Name Server Identifier (NSID) Option
- RFC 5011, Automated Updates of DNS Security (DNSSEC) Trust Anchors
- RFC 5452, Measures for Making DNS More Resilient against Forged Answers
- RFC 5890, Internationalized Domain Names for Applications (IDNA):Definitions and Document Framework
- RFC 5891, Internationalized Domain Names in Applications (IDNA): Protocol
- RFC 5892, The Unicode Code Points and Internationalized Domain Names for Applications (IDNA)
- RFC 5893, Right-to-Left Scripts for Internationalized Domain Names for Applications (IDNA)
- RFC 6891, Extension Mechanisms for DNS (EDNS0)
- RFC 7766, DNS Transport over TCP – Implementation Requirements
Proposed security standards
- RFC 4033, DNS Security Introduction and Requirements
- RFC 4034, Resource Records for the DNS Security Extensions
- RFC 4035, Protocol Modifications for the DNS Security Extensions
- RFC 4509, Use of SHA-256 in DNSSEC Delegation Signer (DS) Resource Records
- RFC 4470, Minimally Covering NSEC Records and DNSSEC On-line Signing
- RFC 5155, DNS Security (DNSSEC) Hashed Authenticated Denial of Existence
- RFC 5702, Use of SHA-2 Algorithms with RSA in DNSKEY and RRSIG Resource Records for DNSSEC
- RFC 5910, Domain Name System (DNS) Security Extensions Mapping for the Extensible Provisioning Protocol (EPP)
- RFC 5933, Use of GOST Signature Algorithms in DNSKEY and RRSIG Resource Records for DNSSEC
- RFC 7830, The EDNS(0) Padding Option
- RFC 7858, Specification for DNS over Transport Layer Security (TLS)
- RFC 8310, Usage Profiles for DNS over TLS and DNS over DTLS
- RFC 8484, DNS Queries over HTTPS (DoH)
- RFC 1183, New DNS RR Definitions
Best Current Practices
- RFC 2182, Selection and Operation of Secondary DNS Servers (BCP 16)
- RFC 2317, Classless IN-ADDR.ARPA delegation (BCP 20)
- RFC 5625, DNS Proxy Implementation Guidelines (BCP 152)
- RFC 6895, Domain Name System (DNS) IANA Considerations (BCP 42)
- RFC 7720, DNS Root Name Service Protocol and Deployment Requirements (BCP 40)
These RFCs are advisory in nature, but may provide useful information despite defining neither a standard or BCP. ( RFC 1796 )
- RFC 1178, Choosing a Name for Your Computer (FYI 5)
- RFC 1591, Domain Name System Structure and Delegation
- RFC 1912, Common DNS Operational and Configuration Errors
- RFC 2100, The Naming of Hosts
- RFC 3696, Application Techniques for Checking and Transformation of Names
- RFC 3833. Threat Analysis of the Domain Name System (DNS)
- RFC 4892, Requirements for a Mechanism Identifying a Name Server Instance
- RFC 5894, Internationalized Domain Names for Applications (IDNA):Background, Explanation, and Rationale
- RFC 5895, Mapping Characters for Internationalized Domain Names in Applications (IDNA) 2008
- RFC 7626, DNS Privacy Considerations
- RFC 7706, Decreasing Access Time to Root Servers by Running One on Loopback
- RFC 8499, DNS Terminology
These RFCs have an official status of Unknown, but due to their age are not intelligibly labeled as such .
- RFC 920, Domain Requirements – Specified original top-level domains
- RFC 1032, Domain Administrators Guide
- RFC 1033, Domain Administrators Operations Guide
- RFC 1101, DNS Encodings of Network Names and Other Types