Domain Name System

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signatures. DNSCrypt uses either TCP or UDP port 443, the same port as HTTPS encrypted web traffic. This introduced not only privacy regarding the content of the query, but also a significant measure of firewall-traversal capability. In 2019, DNSCrypt was further extended to support an "anonymized" mode, similar to the proposed "Oblivious DNS", in which an ingress node receives a query which has been encrypted with the public key of a different server, and relays it to that server, which acts as an egress node, performing the recursive resolution. Privacy of user/query pairs is created, since the ingress node does not know the content of the query, while the egress nodes does not know the identity of the client. DNSCrypt was first implemented in production by

1089: 2761: 1211:. A recursive query is one for which the DNS server answers 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 the query headers. DNS servers are not required to support recursive queries. 822: 1326: 2745:(NIC), also function as registrars to end-users, in addition to providing access to the WHOIS datasets. The top-level domain registries, such as for the domains COM, NET, and ORG use a registry-registrar model consisting of many domain name registrars. In this method of management, the registry only manages the domain name database and the relationship with the registrars. The 767:, 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 the first production-ready version of BIND version 8 in May 1997. Since 2000, over 43 different core developers have worked on BIND. 1147:) 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 the authoritative name servers of the queried domain. With this function implemented in the name server, user applications gain efficiency in design and operation. 2273:(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 wire transmissions of the protocol, but not in any zone files. Initial extensions were also suggested (EDNS0), such as increasing the DNS message size in UDP datagrams. 2460:, in which data is distributed to caching resolvers under the pretense of being an authoritative origin server, thereby polluting the data store with potentially false information and long expiration times (time-to-live). Subsequently, legitimate application requests may be redirected to network hosts operated with malicious intent. 1426:

The DNS is used for efficient storage and distribution of IP addresses of blacklisted email hosts. A common method is to place the IP address of the subject host into the sub-domain of a higher level domain name, and to resolve that name to a record that indicates a positive or a negative indication.

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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 the computer. Computers at educational institutions would

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DNS over HTTPS (DoH) obviates many but not all of the risks, and its transport protocol (i.e. HTTPS) raises concerns of privacy due to (e.g.) 'cookies.' The Tor Network exists to provide TCP circuits with some freedom from tracking, surveillance, and blocking. Thus: In combination with Tor, DoH, and

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as an extension to unencrypted DNS, before DoH was standardized and widely deployed. Apple and Cloudflare subsequently deployed the technology in the context of DoH, as Oblivious DoH (ODoH). ODoH combines ingress/egress separation (invented in ODNS) with DoH's HTTPS tunneling and TLS transport-layer

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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 a time to live (TTL), which indicates how long the information remains valid before it needs to be discarded or refreshed. This

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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

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standards framework, introduced DNS encryption on the downstream side of recursive resolvers, wherein clients encrypt query payloads using servers' public keys, which are published in the DNS (rather than relying upon third-party certificate authorities) and which may in turn be protected by DNSSEC

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use the UPDATE DNS opcode to add or remove resource records dynamically from a zone database maintained on an authoritative DNS server. This facility is useful to register network clients into the DNS when they boot or become otherwise available on the network. As a booting client may be assigned a

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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,

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A label may contain zero to 63 characters. 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. In the internal binary representation of the DNS the maximum length requires 255 octets of storage,

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Some applications such as web browsers maintain an internal DNS cache to avoid repeated lookups via the network. This practice can add extra difficulty when debugging DNS issues as it obscures the history of such data. These caches typically use very short caching times on the order of one minute.

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The DNS resolver will almost invariably have a cache (see above) containing recent lookups. If the cache can provide the answer to the request, the resolver will return the value in the cache to the program that made the request. If the cache does not contain the answer, the resolver will send the

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Originally, security concerns were not major design considerations for DNS software or any software for deployment on the early Internet, as the network was not open for participation by the general public. However, the expansion of the Internet into the commercial sector in the 1990s changed the

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was developed as a competing standard for DNS query transport in 2018, tunneling DNS query data over HTTPS, which transports HTTP over TLS. DoH was promoted as a more web-friendly alternative to DNS since, like DNSCrypt, it uses TCP port 443, and thus looks similar to web traffic, though they are

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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,

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When performing a reverse lookup, the DNS client converts the address into these formats before querying the name for a PTR record following the delegation chain as for any DNS query. For example, assuming the IPv4 address 208.80.152.2 is assigned to Wikimedia, it is represented as a DNS name in

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Solutions preventing DNS inspection by local network operator are criticized for thwarting corporate network security policies and Internet censorship. They are also criticized from a privacy point of view, as giving away the DNS resolution to the hands of a small number of companies known for

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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 a compromise between five competing proposals of solutions to

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We investigate whether DoH traffic is distinguishable from encrypted Web traffic. To this end, we train a machine learning model to classify HTTPS traffic as either Web or DoH. With our DoH identification model in place, we show that an authoritarian ISP can identify ≈97.4% of the DoH packets

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org includes glue along with 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.

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53 for servers listening to queries. Such queries consist of a clear-text request sent in a single UDP packet from the client, responded to with a clear-text reply sent in a single UDP packet from the server. When the length of the answer exceeds 512 bytes and both client and server support

2161:. DNS records belonging to wildcard domain names specify rules for generating resource records within a single DNS zone by substituting whole labels with matching components of the query name, including any specified descendants. For example, in the following configuration, the DNS zone 1107:

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

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is a query of the DNS for domain names when the IP address is known. Multiple domain names may be associated with an IP address. The DNS stores IP addresses in the form of domain names as specially formatted names in pointer (PTR) records within the infrastructure top-level domain

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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

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domain name, a key point of divergence from a traditional phone-book view of the DNS. This process of using 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.

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As a result of this distributed caching 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 conveys basic rules for determining appropriate TTL values.

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represents a notable exception: versions up to IE 3.x cache DNS records for 24 hours by default. Internet Explorer 4.x and later versions (up to IE 8) decrease the default timeout value to half an hour, which may be changed by modifying the default configuration.

1358:, until it either successfully finds a result or does not. It then returns its results to the DNS resolver; assuming it has found a result, the resolver duly caches that result for future use, and hands the result back to the software which initiated the request. 1353:

to set it; however, where systems administrators have configured systems to use their own DNS servers, their DNS resolvers point to separately maintained name servers of the organization. In any event, the name server thus queried will follow the process outlined

589:). The DNS can be quickly and transparently updated, allowing 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 ( 1349:

request to one or more designated DNS servers. In the case of most home users, the Internet service provider to which the machine connects will usually supply this DNS server: such a user will either have configured that server's address manually or allowed

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E-mail servers can query blacklist.example to find out if a specific host connecting to them is in the blacklist. Many of such blacklists, either subscription-based or free of cost, are available for use by email administrators and anti-spam software.

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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 query results for a period of time determined in the configuration

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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 "unknown" record types must not (RFC 3597).

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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 a cache of data.

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is the fully qualified domain name of the node in the tree. On the wire, the name may be shortened using label compression where ends of domain names mentioned earlier in the packet can be substituted for the end of the current domain name.

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ICANN publishes the complete list of TLDs, TLD registries, and domain name registrars. Registrant information associated with domain names is maintained in an online database accessible with the WHOIS service. For most of the more than 290

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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

1309:. For IPv4, the domain is in-addr.arpa. For IPv6, the reverse lookup 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. 2675:, 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 registry. A 2318:(EDNS), larger UDP packets may be used. Use of DNS over UDP is limited by, among other things, its lack of transport-layer encryption, authentication, reliable delivery, and message length. In 1989, RFC 1123 specified optional 2435:

in December 2011. There are several free and open source software implementations that additionally integrate ODoH. It is available for a variety of operating systems, including Unix, Apple iOS, Linux, Android, and Windows.

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The DNS protocol uses two types of DNS messages, queries and responses; both have the same format. Each message consists of a header and four sections: question, answer, authority, and an additional space. A header field

2636:, the browser in Chrome, and the DNS resolver in the 8.8.8.8 service. Would this scenario be a case of a single corporate entity being in a position of overarching control of the entire namespace of the Internet? 2326:. Via fragmentation of long replies, TCP allows longer responses, reliable delivery, and re-use of long-lived connections between clients and servers. For larger responses, the server refers the client to TCP transport. 1317:(ARIN) for the 208.in-addr.arpa zone. ARIN's servers delegate 152.80.208.in-addr.arpa to Wikimedia to which the resolver sends another query for 2.152.80.208.in-addr.arpa, which results in an authoritative response. 2540:

Originally designed as a public, hierarchical, distributed and heavily cached database, DNS protocol has no confidentiality controls. User queries and nameserver responses are being sent unencrypted which enables

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servers. The resolver now queries 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

927:(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. 1035:

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

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Some large ISPs have configured their DNS servers to violate rules, such as by disobeying TTLs, or by indicating that a domain name does not exist just because one of its name servers does not respond.

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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

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When a name server is designated as the authoritative server for a domain name for which it does not have authoritative data, it presents a type of error called a "lame delegation" or "lame response".

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emerged as an IETF standard for encrypted DNS in 2016, utilizing Transport Layer Security (TLS) to protect the entire connection, rather than just the DNS payload. DoT servers listen on TCP port 853.

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The question section has a simpler format than the resource record format used in the other sections. Each question record (there is usually just one in the section) contains the following fields:

985:. 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 is served by the 1156:

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 the local network.

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is needed to specify the mail exchanger IP address. As this has the result of excluding this domain name and its subdomains from the wildcard matches, an additional MX record for the subdomain

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DNS can also "leak" from otherwise secure or private connections, if attention is not paid to their configuration, and at times DNS has been used to bypass firewalls by malicious persons, and

2414:. The privacy gains of Oblivious DNS can be garnered through the use of the preexisting Tor network of ingress and egress nodes, paired with the transport-layer encryption provided by TLS. 1485:

To provide resilience in the event of computer or network failure, multiple DNS servers are usually provided for coverage of each domain. At the top level of global DNS, thirteen groups of

799:(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. 2602:

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

1188:, 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 930:

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,

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The original DNS protocol had limited provisions for extension with new features. In 1999, Paul Vixie published in RFC 2671 (superseded by RFC 6891) an extension mechanism, called

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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.

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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.

1543:. Each field is 16 bits long, and appears in the order given. The identification field is used to match responses with queries. The flag field consists of sub-fields as follows: 510:(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 2301:(UDP) for transport over IP. Its limitations have motivated numerous protocol developments for reliability, security, privacy, and other criteria, in the following decades. 461:

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

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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.

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delivers a result and reduces the load on upstream DNS servers by caching DNS resource records for a period of time after an initial response from upstream DNS servers.

1203:, 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 1313:

reverse order: 2.152.80.208.in-addr.arpa. When the DNS resolver gets a pointer (PTR) request, it begins by querying the root servers, which point to the servers of

2373:. It has "privacy properties similar to DNS over TLS (DoT) , and latency characteristics similar to classic DNS over UDP". This method is not the same as DNS over 1124:

is used in DNS servers to off-load the root servers, and as a result, root name servers actually are involved in only a relatively small fraction of all requests.

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The Domain Name System specifies a database of information elements for network resources. The types of information elements are categorized and organized with a

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e-Infrastructure and e-Services for Developing Countries: 8th International Conference, AFRICOMM 2016, Ouagadougou, Burkina Faso, December 6-7, 2016, Proceedings

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Hostnames and IP addresses are not required to match in a one-to-one relationship. Multiple hostnames may correspond to a single IP address, which is useful in

476:. The Domain Name System maintains the domain name hierarchy and provides translation services between it and the address spaces. Internet name servers and a 1656:

After the flags word, 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.

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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.

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used a DoH-resolution mechanism to bypass local DNS resolution and steer all DNS queries from Apple's platforms to a set of Apple-operated name resolvers?

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specifies that opportunistic encryption and authenticated encryption may be supported, but did not make either server or client authentication mandatory.

1341:, and other Internet applications. When an application makes a request that requires a domain name lookup, such programs send a resolution request to the 1104:) of the known addresses of the root name servers. The hints are updated periodically by an administrator by retrieving a dataset from a reliable source. 2668: 616:

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

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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

2953: 2734:, etc., etc.) holds basic WHOIS data (i.e., registrar and name servers, etc.). Organizations, or registrants using ORG on the other hand, are on the 388: 4209: 2479:, add support for cryptographic authentication between trusted peers and are commonly used to authorize zone transfer or dynamic update operations. 5314: 1092:

A DNS resolver that implements the iterative approach mandated by RFC 1034; in this case, the resolver consults three name servers to resolve the

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already fielded an app that used its own DNS resolution mechanism independent of the platform upon which the app was running. What if the

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User privacy is further exposed by proposals for increasing the level of client IP information in DNS queries (RFC 7871) for the benefit of

1284:, i.e. the caching of the fact of non-existence of a record, is determined by name servers authoritative for a zone which must include the 683:

Addresses were assigned manually. Computers, including their hostnames and addresses, were added to the primary file by contacting the SRI

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developed and maintained the first ARPANET directory. Maintenance of numerical addresses, called the Assigned Numbers List, was handled by

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The Domain Name System delegates the responsibility of assigning domain names and mapping those names to Internet resources by designating

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Users generally do not communicate directly with a DNS resolver. Instead DNS resolution takes place transparently in applications such as

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provides a mapping between a domain and a mail exchanger; this can provide an additional layer of fault tolerance and load distribution.

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Public DNS servers can be queried using traditional DNS protocol, in which case they provide no protection from local surveillance, or

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TTL is determined by the administrator of the authoritative DNS server and can range from a few seconds to several days or even weeks.

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is a person or organization who asked for domain registration. The registry receives registration information from each domain name

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service and was designed to avoid a single large central database. In addition, the DNS specifies the technical functionality of the

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is responsible for operating the database of names within its authoritative zone, although the term is most often used for TLDs. A

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Administrative responsibility for any zone may be divided by creating additional zones. Authority over the new zone is said to be

3084: 2703:(ccTLDs), the domain registries maintain the WHOIS (Registrant, name servers, expiration dates, etc.) information. For instance, 3970:

James F. Kurose and Keith W. Ross, Computer Networking: A Top-Down Approach, 6th ed. Essex, England: Pearson Educ. Limited, 2012

2468: 1963: 1314: 434:) assigned to each of the associated entities. Most prominently, it translates readily memorized domain names to the numerical 4315: 2490:

are different names, yet users may be unable to distinguish them in a graphical user interface depending on the user's chosen

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published the original specifications in RFC 882 and RFC 883 in November 1983. These were updated in RFC 973 in January 1986.

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These RFCs are advisory in nature, but may provide useful information despite defining neither a standard or BCP. (RFC 1796)

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the principle of "Don't Do That, Then" (DDTT) to mitigate request fingerprinting, I describe DNS over HTTPS over Tor (DoHoT).

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monetizing user traffic and for centralizing DNS name resolution, which is generally perceived as harmful for the Internet.

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The domain name is broken into discrete labels which are concatenated; each label is prefixed by the length of that label.

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Some resolvers may override TTL values, as the protocol supports caching for up to sixty-eight years or no caching at all.

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The definitive descriptions of the rules for forming domain names appear in RFC 1035, RFC 1123, RFC 2181, and RFC 5892. A

238: 233: 203: 2557:. This deficiency is commonly used by cybercriminals and network operators for marketing purposes, user authentication on 5239: 1350: 1137:

of the Domain Name System and each user system would have to implement resolver software capable of recursive operation.

63: 4112: 3945: 2887:"Information fusion-based method for distributed domain name system cache poisoning attack detection and identification" 2749:(users of a domain name) are customers of the registrar, in some cases through additional subcontracting of resellers. 1062:

in its responses. This flag is usually reproduced prominently in the output of DNS administration query tools, such as

725: 310: 253: 178: 17: 2129:, the domain name system also defines several request types that are used only in communication with other DNS nodes ( 4529: 2780: 2692: 2687:, which is authorized (accredited) to assign names in the corresponding zone and publishes the information using the 814:

may consist of as many domains and subdomains as the zone manager chooses. DNS can also be partitioned according to

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is the record type. It indicates the format of the data and it gives a hint of its intended use. For example, the

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Response code, can be NOERROR (0), FORMERR (1, Format error), SERVFAIL (2), NXDOMAIN (3, Nonexistent domain), etc.

3563: 3511: 3462: 3421: 3045: 2427: 2366: 1499:(DDNS) updates a DNS server with a client IP address on-the-fly, for example, when moving between ISPs or mobile 718: 644:

services. That data can be used to gain insight on, and track responsibility for, a given host on the Internet.

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network, all records (answer, authority, and additional sections) use the common format specified in RFC 1035:

1954:(RRset), having no special ordering. DNS resolvers return the entire set upon query, but servers may implement 677: 123: 113: 3383: 2855: 2700: 2522: 2507: 2319: 947: 935: 756: 740: 538: 243: 223: 173: 1292:

field of the SOA record and the TTL of the SOA itself is used to establish the TTL for the negative answer.

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in the DNS protocol in communication with its primary to maintain an identical copy of the primary records.

4264: 3873: 2971: 2946: 2835: 2315: 2270: 2134: 428: 163: 158: 153: 4493: 2122:(HS) exist. Each class is an independent name space with potentially different delegations of DNS zones. 2114:) for common DNS records involving Internet hostnames, servers, or IP addresses. In addition, the classes 1592:

Authoritative Answer, in a response, indicates if the DNS server is authoritative for the queried hostname

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The type can be QUERY (standard query, 0), IQUERY (inverse query, 1), or STATUS (server status request, 2)

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In this case, the name server providing the delegation must also provide one or more IP addresses for the

442:. The Domain Name System has been an essential component of the functionality of the Internet since 1985. 5329: 5319: 4168: 1114: 1093: 871:

The hierarchy of domains descends from right to left; each label to the left specifies a subdivision, or

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For proper operation of its domain name resolver, a network host is configured with an initial cache (

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registry approach, i.e. keeping the WHOIS data in central registries instead of registrar databases.

2181:, as well as a wildcarded MX record for all of its subdomains, must also be defined in the DNS zone. 1255: 1236: 1063: 1026: 628:

The DNS reflects the structure of administrative responsibility on the Internet. Each subdomain is a

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Domain Name System (DNS) Security Extensions Mapping for the Extensible Provisioning Protocol (EPP)

4412: 2947:"Globally Distributed Content Delivery, IEEE Internet Computing, September/October 2002, pp. 50–58" 2850: 2735: 2708: 2569: 2554: 2096:

record specifies the mail server used to handle mail for a domain specified in an e-mail address.

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In November 1987, RFC 1034 and RFC 1035 superseded the 1983 DNS specifications. Several additional

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The right to use a domain name is delegated by domain name registrars which are accredited by the

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may appear identical on typical computer screens. This vulnerability is occasionally exploited in

2410:. A use which has become common since 2019 to warrant its own frequently used acronym is DNS over 4464:"Registration Data Access Protocol (RDAP) Operational Profile for gTLD Registries and Registrars" 3920: 3824: 3279: 2805: 2464: 2456:

Several vulnerability issues were discovered and exploited by malicious users. One such issue is

2403: 978: 462: 360: 350: 143: 58: 42: 2886: 2820: 2800: 2298: 537:(UDP) as transport over IP. Reliability, security, and privacy concerns spawned the use of the 534: 477: 228: 78: 1010: 652:

Using a simpler, more memorable name in place of a host's numerical address dates back to the

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Internationalized Domain Names for Applications (IDNA):Background, Explanation, and Rationale

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of their allocated name space to other name servers. This mechanism provides distributed and

355: 128: 3553: 3501: 3360: 3300: 1946:, the resource records (RRs). Each record has a type (name and number), an expiration time ( 4339: 4150: 4050: 3717: 3643: 3577: 3525: 3476: 3435: 3133: 3059: 2775: 2503: 2386: 1625:

Recursion Available, in a response, indicates if the replying DNS server supports recursion

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DNS serves other purposes in addition to translating names to IP addresses. For instance,

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to a designated name server. The parent zone ceases to be authoritative for the new zone.

612:. When a user accesses a distributed Internet service using a URL, the domain name of the 8: 4736:

Internationalized Domain Names for Applications (IDNA):Definitions and Document Framework

2562: 2457: 2146: 1950:), a class, and type-specific data. Resource records of the same type are described as a 1412: 1229: 550: 4471: 2935:, Information Sciences Institute, J. Postel (Ed.), The Internet Society (September 1981) 728:

students, Douglas Terry, Mark Painter, David Riggle, and Songnian Zhou, wrote the first

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The most common types of records stored in the DNS database are for start of authority (

4394: 4201: 4183: 2994: 2914: 2407: 1947: 1301: 1088: 503: 345: 2035:

Count of seconds that the RR stays valid (The maximum is 2−1, which is about 68 years)

818:

where the separate classes can be thought of as an array of parallel namespace trees.

438:

needed for locating and identifying computer services and devices with the underlying

4525: 4386: 3804: 3777: 3654: 3606: 3158: 2998: 2906: 2845: 2582:, which move DNS resolution to the VPN operator and hide user traffic from local ISP, 2529: 2323: 1989: 1970: 1892: 1684: 1374: 1046:

An authoritative server indicates its status of supplying definitive answers, deemed

744: 657: 519: 518:(RP) records. As a general purpose database, the DNS has also been used in combating 507: 418: 273: 49: 4398: 4205: 3899: 3215:"Why Does the Net Still Work on Christmas? Paul Mockapetris - Internet Hall of Fame" 2918: 2760: 887:

is a subdomain of example.com. This tree of subdivisions may have up to 127 levels.

702:, for example. She and her team managed the Host Naming Registry from 1972 to 1989. 4378: 4193: 4140: 4090: 4040: 4008: 3746: 3707: 3633: 3567: 3515: 3466: 3425: 3329: 3123: 3049: 2986: 2898: 2790: 2338: 2254: 2246: 1486: 1288:(SOA) record when reporting no data of the requested type exists. The value of the 1260: 1251:

of the response. A glue record is a combination of the name server and IP address.

994: 986: 959: 861: 707: 439: 4756:

The Unicode Code Points and Internationalized Domain Names for Applications (IDNA)

1345:

in the local operating system, which in turn handles the communications required.

965:) have adopted the IDNA system, guided by RFC 5890, RFC 5891, RFC 5892, RFC 5893. 5123:

Mapping Characters for Internationalized Domain Names in Applications (IDNA) 2008

4419: 2766: 2542: 1955: 1500: 1401: 1397: 604:

function of the DNS is its central role in distributed Internet services such as

214: 5213: 5203: 5193: 5158: 5148: 5138: 5128: 5118: 5108: 5098: 5088: 5078: 5068: 5058: 5048: 5037: 5016: 5005: 4994: 4983: 4972: 4955: 4938: 4928: 4918: 4908: 4903:

Use of GOST Signature Algorithms in DNSKEY and RRSIG Resource Records for DNSSEC

4898: 4888: 4883:

Use of SHA-2 Algorithms with RSA in DNSKEY and RRSIG Resource Records for DNSSEC

4878: 4868: 4858: 4848: 4838: 4828: 4818: 4801: 4791: 4781: 4771: 4766:

Right-to-Left Scripts for Internationalized Domain Names for Applications (IDNA)

4761: 4751: 4741: 4731: 4721: 4711: 4701: 4691: 4681: 4671: 4661: 4651: 4641: 4631: 4621: 4611: 4601: 4591: 4581: 4571: 4561: 4551: 4153: 4134: 4094: 4078: 4074: 4070: 4066: 4062: 4053: 4034: 4012: 3720: 3701: 3681: 3677: 3673: 3669: 3646: 3627: 3580: 3557: 3528: 3505: 3479: 3456: 3438: 3415: 3136: 3117: 3062: 3039: 2342: 2258: 2250: 1243:. The delegating name server provides this glue in the form of records in the 1068:

that the responding name server is an authority for the domain name in question.

526:(RBL). The DNS database is traditionally stored in a structured text file, the 5182: 4366: 2810: 2610: 2558: 2450: 2446: 2353: 2289:

server, it is not possible to provide static DNS assignments for such clients.

1281: 864:; for example, the domain name www.example.com belongs to the top-level domain 664:

that mapped host names to the numerical addresses of computers on the ARPANET.

594: 499: 458: 454: 264: 5231: 2902: 735:

implementation for the Berkeley Internet Name Domain, commonly referred to as

5308: 4390: 4197: 3349:

Elizabeth Feinler, IEEE Annals, 3B2-9 man2011030074.3d 29/7/011 11:54 Page 74

2910: 2830: 2795: 2593: 2585: 2546: 2411: 1603:

TrunCation, indicates that this message was truncated due to excessive length

1382: 1338: 1134: 807: 605: 473: 3454: 2990: 2380: 946:. In 2009, ICANN approved the installation of internationalized domain name 5253: 3697: 3113: 2972:"The Akamai Network: A Platform for High-Performance Internet Applications" 2815: 2614: 2599: 2550: 2471:(DNSSEC) modify DNS to add support for cryptographically signed responses. 2334: 2081: 2030: 1342: 1143: 854: 764: 661: 632:

of administrative autonomy delegated to a manager. For zones operated by a

410: 183: 5271: 1408:

to multiple server instances across an enterprise or the global Internet.

710:. Mockapetris instead created the Domain Name System in 1983 while at the 2840: 2603: 2475:

has been proposed as an alternative to DNSSEC. Other extensions, such as

2310: 2281: 1966:(DNSSEC) work on the complete set of resource record in canonical order. 1496: 1385:

detects issues with the DNS server it displays a specific error message.

1334: 1204: 1165: 982: 846: 732: 562: 492: 423: 5249:"Meet the seven people who hold the keys to worldwide internet security" 4382: 2575:

The main approaches that are in use to counter privacy issues with DNS:

2482:

Some domain names may be used to achieve spoofing effects. For example,

4030: 2944:

J. Dilley, B. Maggs, J. Parikh, H. Prokop, R. Sitaraman, and B. Weihl.

2645: 1285: 760: 748: 669: 597:

without having to know how the computer actually locates the services.

484: 435: 331: 4411:

APWG. "Global Phishing Survey: Domain Name Use and Trends in 1H2010."

2165:

specifies that all subdomains, including subdomains of subdomains, of

1393:

The Domain Name System includes several other functions and features.

1207:

typically makes a recursive query to the DNS server run by the user's

5272:"Internet Governance and the Domain Name System: Issues for Congress" 5235: 4145: 4045: 3750: 3712: 3638: 3572: 3520: 3471: 3430: 3128: 3054: 2860: 2511: 2126: 1420: 938:(IDNA) system, by which user applications, such as web browsers, map 872: 688: 636:, administrative information is often complemented by the registry's 527: 469: 450: 2385:

Oblivious DNS (ODNS) was invented and implemented by researchers at

821: 449:

for each domain. Network administrators may delegate authority over

5292: 4188: 3877: 3379: 2865: 2731: 2641: 2618: 2515: 2491: 2472: 2423: 2261:

was incomplete and resulted in misinterpretations by implementers.

2115: 2089: 1325: 943: 811: 684: 629: 554: 414: 4646:

DNSSEC and IPv6 A6 aware server/resolver message size requirements

4367:"Retrofitting Security into Network Protocols: The Case of DNSSEC" 3455:

Paul Hoffman; Andrew Sullivan; Kazunori Fujiwara (December 2015).

1614:

Recursion Desired, indicates if the client means a recursive query

1489:

exist, with additional "copies" of them distributed worldwide via

549:

An often-used analogy to explain the DNS is that it serves as the

4308: 4133:

Huitema, Christian; Dickinson, Sara; Mankin, Allison (May 2022).

2969: 2933:

Internet Protocol - DARPA Internet Program Protocol Specification

2727: 2723: 2672: 2637: 2432: 1490: 939: 653: 4853:

Use of SHA-256 in DNSSEC Delegation Signer (DS) Resource Records

4596:

A Mechanism for Prompt Notification of Zone Changes (DNS NOTIFY)

3367:. USENIX Association Software Tools Users Group. pp. 23–31. 2502:

look very similar or even identical. This problem, known as the

5103:

Requirements for a Mechanism Identifying a Name Server Instance

5083:

Application Techniques for Checking and Transformation of Names

4746:

Internationalized Domain Names in Applications (IDNA): Protocol

4521:

Broad Band: The Untold Story of the Women Who Made the Internet

4320: 3703:

Application Techniques for Checking and Transformation of Names

2707:, Germany NIC, holds the DE domain data. From about 2001, most 2589: 2374: 1416: 1181:. A resolution process may use a combination of these methods. 511: 294: 188: 87: 67: 4873:

DNS Security (DNSSEC) Hashed Authenticated Denial of Existence

3900:"Ben Anderson: Why Web Browser DNS Caching Can Be A Bad Thing" 4726:

Measures for Making DNS More Resilient against Forged Answers

4467: 2704: 2688: 2592:

domains, hiding both name resolution and user traffic behind

2133:), such as when performing zone transfers (AXFR/IXFR) or for 1306: 931: 896: 692: 641: 315: 93: 4121:

correctly while only misclassifying 1 in 10,000 Web packets.

4028: 3737:

Fujiwara, Kazunori; Sullivan, Andrew; Hoffman, Paul (2024).

2322:(TCP) transport for DNS queries, replies and, particularly, 5298: 3949: 3921:"How Internet Explorer uses the cache for DNS host entries" 2885:

Wu, Hao; Dang, Xianglei; Wang, Lidong; He, Longtao (2016).

2588:, which replaces traditional DNS resolution with anonymous 2476: 2370: 2286: 1037: 840: 736: 729: 698: 586: 574: 496: 283: 278: 248: 198: 118: 83: 5021:

DNS Root Name Service Protocol and Deployment Requirements

4863:

Minimally Covering NSEC Records and DNSSEC On-line Signing

4265:""No Port 53, Who Dis?" A Year of DNS over HTTPS over Tor" 2357:

easily differentiable in practice without proper padding.

1219:

then a "com" server, and finally an "example.com" server.

4923:

Specification for DNS over Transport Layer Security (TLS)

4676:

Domain Name System (DNS) Case Insensitivity Clarification

3770:

Nemeth, Evi; Snyder, Garth; Hein, Trent R. (2006-10-30).

3629:

Domain Name System (DNS) Case Insensitivity Clarification

3209: 3207: 2649: 2579: 2381:

Oblivious DoH (ODoH) and predecessor Oblivious DNS (ODNS)

2297:

From the time of its origin in 1983 the DNS has used the

1689: 1559: 1469:. This hostname is either not configured, or resolves to 1222: 1208: 1059: 613: 590: 417:, services, and other resources on the Internet or other 103: 5177:, but due to their age are not clearly labeled as such. 4716:

Automated Updates of DNS Security (DNSSEC) Trust Anchors

4166: 3252: 2088:

record lists which name servers can answer lookups on a

1247:

of the DNS response, and provides the delegation in the

1239:

mentioned in the delegation. This information is called

553:

for the Internet by translating human-friendly computer

4576:

Requirements for Internet Hosts—Application and Support

4167:

Schmitt, Paul; Edmundson, Anne; Feamster, Nick (2019).

4111:

Csikor, Levente; Divakaran, Dinil Mon (February 2021).

3736: 3377: 3230: 3228: 541:(TCP) as well as numerous other protocol developments. 4843:

Protocol Modifications for the DNS Security Extensions

4606:

Dynamic Updates in the domain name system (DNS UPDATE)

4132: 4036:

Dynamic Updates in the Domain Name System (DNS UPDATE)

3204: 1570:

Indicates if the message is a query (0) or a reply (1)

421:(IP) networks. It associates various information with 4270:. Network and Distributed System Security Symposium. 2080:

record is used to translate from a domain name to an

1519:

The header section consists of the following fields:

4806:

Secret Key Transaction Authentication for DNS (TSIG)

4796:

DNS Transport over TCP - Implementation Requirements

3797:

Bissyande, Tegawendé F.; Sie, Oumarou (2017-10-09).

3240: 3225: 3201:

IEEE Annals man2011030074.3d 29/7/011 11:54 Page 74

3183: 3075: 2756: 1127: 829:, organized into zones, each served by a name server 774:

have proposed extensions to the core DNS protocols.

3365:

Summer Conference, Salt Lake City 1984: Proceedings

3359:Terry, Douglas B.; et al. (June 12–15, 1984). 3171: 2722:registry model is used. The domain registry (e.g., 2669:

Internet Corporation for Assigned Names and Numbers

2632:Google is the dominant provider of the platform in 1503:, or when the IP address changes administratively. 875:of the domain to the right. For example, the label 4666:Handling of Unknown DNS Resource Record (RR) Types 4294:"DNSCrypt – Critical, fundamental, and about time" 4169:"Oblivious DNS: Practical Privacy for DNS Queries" 3323: 2426:protocol, which was developed in 2011 outside the 849:consists of one or more parts, technically called 4933:Usage Profiles for DNS over TLS and DNS over DTLS 4113:"Privacy of DNS over HTTPS: Requiem for a Dream?" 3603:International Domain Name Law: ICANN and the UDRP 3358: 3352: 1355: 5306: 5295:, Open Source Guide – DNS for Rocket Scientists. 4977:Selection and Operation of Secondary DNS Servers 4833:Resource Records for the DNS Security Extensions 4227:"Oblivious DNS Deployed by Cloudflare and Apple" 3769: 3551: 3499: 2011:Type of RR in numeric form (e.g., 15 for MX RRs) 1415:use DNS to find the best mail server to deliver 5093:Threat Analysis of the Domain Name System (DNS) 5063:Common DNS Operational and Configuration Errors 4686:The Role of Wildcards in the Domain Name System 4566:Domain Names - Implementation and Specification 4364: 4110: 4029:S. Thomson; Y. Rekhter; J. Bound (April 1997). 4017:The Role of Wildcards in the Domain Name System 3625: 3041:Domain Names - Implementation and Specification 2525:can also be used to help validate DNS results. 1516:) controls the content of these four sections. 1080: 942:strings into the valid DNS character set using 936:Internationalizing Domain Names in Applications 691:during business hours. Later, Feinler set up a 5218:DNS Encodings of Network Names and Other Types 5153:DNS Query Name Minimisation to Improve Privacy 4811: 4429: 4427: 4340:"Oblivious DoH · DNSCrypt/dnscrypt-proxy Wiki" 3371: 2970:Nygren., E.; Sitaraman R. K.; Sun, J. (2010). 2711:(gTLD) registries have adopted this so-called 2535: 2445:requirements for security measures to protect 2000:Name of the node to which this record pertains 857:, and delimited by dots, such as example.com. 825:The hierarchical Domain Name System for class 743:substantially revised the DNS implementation. 5301:– site where you can do experiments with DNS. 3559:Domain Names - Domain Concepts and Facilities 3507:Domain Names - Domain Concepts and Facilities 3417:Domain Names - Domain Concepts and Facilities 2304: 2125:In addition to resource records defined in a 1017:An authoritative name server can either be a 1009:name server is a name server that only gives 557:into IP addresses. For example, the hostname 382: 5010:Domain Name System (DNS) IANA Considerations 4626:Negative Caching of DNS Queries (DNS NCACHE) 4365:Herzberg, Amir; Shulman, Haya (2014-01-01). 3994:Domain Name System (DNS) IANA Considerations 3983:, D. Eastlake 3rd (November 2008), Section 3 3981:Domain Name System (DNS) IANA Considerations 3897: 3796: 2884: 2467:, leading to many attack possibilities; the 2245:The role of wildcard records was refined in 1000: 5053:Domain Name System Structure and Delegation 4424: 4332: 3659:: CS1 maint: numeric names: authors list ( 3547: 3545: 3502:"Name space specifications and terminology" 3413: 3157:(5th ed.). O'Reilly Media. p. 3. 3037: 2662: 2532:data, since it is often seen as innocuous. 2046:Length of RDATA field (specified in octets) 680:(ISI), whose team worked closely with SRI. 533:The Domain Name System originally used the 4823:DNS Security Introduction and Requirements 4004: 4002: 3696: 3692: 3690: 3450: 3448: 3409: 3407: 3405: 3403: 3401: 3361:"The Berkeley Internet Name Domain Server" 3301:"Paul Mockapetris | Internet Hall of Fame" 3112: 2741:Some domain name registries, often called 2463:DNS responses traditionally do not have a 1050:, by setting a protocol flag, called the " 973:The Domain Name System is maintained by a 891:as it also stores the length of the name. 656:era. The Stanford Research Institute (now 389: 375: 30:"DNS" redirects here. For other uses, see 5133:Running a Root Server Local to a Resolver 4965: 4187: 4144: 4044: 3711: 3637: 3571: 3519: 3470: 3429: 3152: 3127: 3053: 3033: 3031: 3029: 3027: 3025: 3023: 2786:Decentralized object location and routing 1228:delegation is being provided, there is a 530:, but other database systems are common. 27:System to identify resources on a network 4706:DNS Name Server Identifier (NSID) Option 4291: 3996:, D. Eastlake 3rd (November 2008), p. 11 3554:"How the database is divided into zones" 3542: 3493: 2718:For top-level domains on COM and NET, a 2149:which specify names that start with the 1324: 1087: 989:, the servers to query when looking up ( 958:of the existing top-level domain names ( 923:, and hyphen. This rule is known as the 899:character set, consisting of characters 841:Domain name syntax, internationalization 820: 5315:Internet properties established in 1983 5270:Kruger, Lennard G. (18 November 2016). 4616:Clarifications to the DNS Specification 4262: 4022: 3999: 3687: 3619: 3600: 3445: 3398: 3324:Andrei Robachevsky (26 November 2013). 2671:(ICANN) or other organizations such as 2348: 2276: 1192:, the non-recursive query of its local 1108:"www.wikipedia.org" is referred to the 620:receive different translations for the 472:, the domain name hierarchy and the IP 14: 5307: 5269: 5208:Domain Administrators Operations Guide 5189:– Specified original top-level domains 5173:These RFCs have an official status of 4656:DNS Extensions to Support IP Version 6 4556:Domain Names - Concepts and Facilities 4433: 3106: 3076:Champika Wijayatunga (February 2015). 3020: 2469:Domain Name System Security Extensions 2360: 2292: 2285:different IP address each time from a 2264: 1964:Domain Name System Security Extensions 1797: 1315:American Registry for Internet Numbers 1223:Circular dependencies and glue records 791:. Each node or leaf in the tree has a 514:records, or for human queries such as 502:(MX), name servers (NS), pointers for 5229: 5027: 4636:Indicating Resolver Support of DNSSEC 4517: 4328:from the original on 25 October 2019. 4247: 3946:"Domain Name System (DNS) Parameters" 3258: 3246: 3234: 3189: 3177: 2925: 2329: 2253:, because the original definition in 1506: 1388: 981:. The nodes of this database are the 468:The Internet maintains two principal 5246: 4948: 4786:Extension Mechanisms for DNS (EDNS0) 4118:. National University of Singapore. 4099:Extension Mechanisms for DNS (EDNS0) 3605:. Bloomsbury Publishing. p. 8. 3119:Role of the Domain Name System (DNS) 2826:IPv6 brokenness and DNS whitelisting 1537:Number of authority resource records 787:The domain name space consists of a 782: 409:) is a hierarchical and distributed 5257:. Guardian News & Media Limited 5242:from the original on 29 March 2023. 4999:DNS Proxy Implementation Guidelines 4696:HMAC SHA TSIG Algorithm Identifiers 4316:"Anonymized DNSCrypt specification" 4292:Ulevitch, David (6 December 2011). 4139:. Internet Engineering Task Force. 4136:DNS over Dedicated QUIC Connections 3414:Mockapetris, Paul (November 1987). 3153:Liu, Cricket; Albitz, Paul (2006). 3038:Mockapetris, Paul (November 1987). 2979:ACM SIGOPS Operating Systems Review 2506:, is acute in systems that support 2365:RFC 9250, published in 2022 by the 2140: 1937: 1914:Type of RR (A, AAAA, MX, TXT, etc.) 1871: 1361: 1189: 1121: 24: 4544: 4539: 3552:Paul Mockapetris (November 1987). 3500:Paul Mockapetris (November 1987). 2621:, which do provide such protection 2439: 581:2606:2800:220:1:248:1893:25c8:1946 413:that provides a naming system for 25: 5341: 5223: 5042:Choosing a Name for Your Computer 4988:Classless IN-ADDR.ARPA delegation 4776:Non-Terminal DNS Name Redirection 4470:. 3 December 2015. Archived from 4304:from the original on 1 July 2020. 4277:from the original on 2021-03-21. 4248:Pauly, Tommy (2 September 2021). 3898:Ben Anderson (7 September 2011). 2781:Comparison of DNS server software 2394:encryption in a single protocol. 1465:is not blacklisted and points to 1295: 1267: 1128:Recursive and caching name server 860:The right-most label conveys the 751:then took over BIND maintenance. 712:University of Southern California 674:University of Southern California 5247:Ball, James (28 February 2014). 4586:Incremental Zone Transfer in DNS 4452:from the original on 2019-09-30. 4215:from the original on 2022-01-21. 3626:D. Eastlake 3rd (January 2006). 2959:from the original on 2015-04-17. 2759: 2691:protocol. As of 2015, usage of 2145:The domain name system supports 1320: 1159: 948:country code top-level domains ( 687:(NIC), directed by Feinler, via 4524:. New York: Portfolio/Penguin. 4486: 4456: 4405: 4358: 4285: 4263:Muffett, Alec (February 2021). 4256: 4241: 4219: 4160: 4126: 4104: 4084: 3986: 3973: 3964: 3938: 3913: 3891: 3866: 3842: 3817: 3790: 3776:. Addison-Wesley Professional. 3763: 3730: 3594: 3386:from the original on 2019-06-30 3343: 3317: 3293: 3264: 3195: 3094:from the original on 2015-12-22 3008:from the original on 2010-12-02 2397: 2367:Internet Engineering Task Force 1025:server. Historically the terms 968: 719:Internet Engineering Task Force 660:) maintained a text file named 5279:Congressional Research Service 4176:Privacy Enhancing Technologies 3146: 3069: 2963: 2938: 2878: 2701:country code top-level domains 2508:internationalized domain names 2110:of a record is set to IN (for 1903:Name of the requested resource 678:Information Sciences Institute 13: 1: 4443:The Internet Protocol Journal 3874:"Providers ignoring DNS TTL?" 3773:Linux Administration Handbook 3378:Internet Systems Consortium. 2872: 2856:List of managed DNS providers 2523:forward-confirmed reverse DNS 2510:, as many character codes in 2320:Transmission Control Protocol 1636:Zero, reserved for future use 1467:6.113.0.203.blacklist.example 1444:5.113.0.203.blacklist.example 1442:is blacklisted. It points to 879:specifies a subdomain of the 539:Transmission Control Protocol 4943:DNS Queries over HTTPS (DoH) 2836:Public recursive name server 2316:Extension Mechanisms for DNS 2271:Extension Mechanisms for DNS 2169:use the mail exchanger (MX) 1977:Resource record (RR) fields 1880:Resource record (RR) fields 1081:Address resolution mechanism 1075: 1038:automatic updating mechanism 777: 565:translates to the addresses 7: 5325:Application layer protocols 5198:Domain Administrators Guide 4812:Proposed security standards 4434:Huston, Geoff (July 2019). 3326:"Happy 30th Birthday, DNS!" 2752: 2743:network information centers 2536:Privacy and tracking issues 2494:. In many fonts the letter 2417: 2057:Additional RR-specific data 1115:fully qualified domain name 1094:fully qualified domain name 753:Internet Systems Consortium 739:. In 1985, Kevin Dunlap of 544: 10: 5346: 5230:Vixie, Paul (4 May 2007). 5168: 5143:DNS Privacy Considerations 4913:The EDNS(0) Padding Option 4511: 4436:"DNS Privacy and the IETF" 4250:"Oblivious DNS Over HTTPS" 4081:. 3850:"What is DNS propagation?" 3684:. 2644:app included DoH? What if 2305:DNS over UDP/TCP/53 (Do53) 2060:Variable, as per RDLENGTH 1864: 1861: 1850: 1847: 1800: 1154:Internet service providers 853:, that are conventionally 802:The tree sub-divides into 685:Network Information Center 647: 447:authoritative name servers 29: 4518:Evans, Claire L. (2018). 4039:. Network Working Group. 3706:. Network Working Group. 3632:. Network Working Group. 3122:. Network Working Group. 2903:10.1049/iet-ifs.2014.0386 2606:or pornography blocking. 2570:Content Delivery Networks 2555:man-in-the-middle attacks 1865:Number of additional RRs 1836: 1833: 1810: 1794: 1791: 1678: 1675: 1672: 1669: 1664: 1256:authoritative name server 1237:authoritative name server 1001:Authoritative name server 610:content delivery networks 4198:10.2478/popets-2019-0028 4101:, P. Vixie (August 1999) 2891:IET Information Security 2851:List of DNS record types 2736:Public Interest Registry 2709:Generic top-level domain 2663:Domain name registration 2657:DNS Privacy and the IETF 2404:virtual private networks 2183: 1944:list of DNS record types 1862:Number of authority RRs 1541:Number of additional RRs 524:real-time blackhole list 4371:IEEE Internet Computing 3601:Lindsay, David (2007). 2991:10.1145/1842733.1842736 2806:DNS management software 2543:network packet sniffing 2465:cryptographic signature 1329:DNS resolution sequence 977:system, which uses the 755:was founded in 1994 by 561:within the domain name 463:Internet protocol suite 43:Internet protocol suite 4966:Best Current Practices 4960:New DNS RR Definitions 4065:. Updated by RFC 4019:, E. Lewis (July 2006) 3305:internethalloffame.org 3219:internethalloffame.org 2821:Hierarchical namespace 2801:DNS Long-Lived Queries 2660: 2299:User Datagram Protocol 1330: 1097: 830: 535:User Datagram Protocol 478:communication protocol 3925:Microsoft Corporation 3380:"The History of BIND" 3276:Internet Hall of Fame 2695:is being considered. 2630: 2596:counter-surveillance, 2391:University of Chicago 2369:, describes DNS over 1328: 1117:"www.wikipedia.org". 1091: 824: 747:, Phil Almquist, and 3668:Updated by RFC 3282:on 14 September 2018 3078:"DNS Abuse Handling" 2776:Alternative DNS root 2504:IDN homograph attack 2402:DNS may be run over 2387:Princeton University 2349:DNS over HTTPS (DoH) 2277:Dynamic zone updates 2147:wildcard DNS records 1956:round-robin ordering 1848:Number of questions 1547:Header flags format 1446:, which resolves to 1413:mail transfer agents 1254:For example, if the 1190:caching DNS resolver 1096:"www.wikipedia.org". 1052:Authoritative Answer 975:distributed database 954:. In addition, many 772:Request for Comments 522:(spam) by storing a 32:DNS (disambiguation) 5187:Domain Requirements 5073:The Naming of Hosts 4474:on 22 December 2015 4413:10/15/2010 apwg.org 4383:10.1109/MIC.2014.14 3672:. Updates RFC 3382:. History of BIND. 3272:"Elizabeth Feinler" 2551:DNS cache poisoning 2521:Techniques such as 2458:DNS cache poisoning 2408:tunneling protocols 2361:DNS over QUIC (DoQ) 2293:Transport protocols 2282:Dynamic DNS updates 2265:Protocol extensions 2173:. The A record for 1978: 1962:. In contrast, the 1952:resource record set 1881: 1661: 1548: 1529:Number of questions 1230:circular dependency 1186:non-recursive query 979:client–server model 789:tree data structure 508:domain name aliases 504:reverse DNS lookups 5330:Internet Standards 5320:Domain Name System 5028:Informational RFCs 4494:"Find a Registrar" 4418:2012-10-03 at the 4346:. DNSCrypt project 4059:Proposed Standard. 3854:IONOS Digitalguide 3829:IONOS Digitalguide 3666:Proposed Standard. 3261:, p. 120–121. 2330:DNS over TLS (DoT) 1976: 1969:When sent over an 1879: 1851:Number of answers 1659: 1546: 1507:DNS message format 1389:Other applications 1331: 1302:reverse DNS lookup 1286:Start of Authority 1245:additional section 1098: 831: 516:responsible person 403:Domain Name System 18:Domain name system 4949:Experimental RFCs 4229:. 9 December 2020 4061:Updates RFC 3831:. 27 January 2022 3810:978-3-319-66742-3 3783:978-0-13-700275-7 3739:"DNS Terminology" 3700:(February 2004). 3612:978-1-84113-584-7 3566:. sec. 4.2. 3514:. sec. 3.1. 3164:978-0-596-10057-5 3116:(February 2003). 2846:Split-horizon DNS 2064: 2063: 1971:Internet Protocol 1932: 1931: 1869: 1868: 1654: 1653: 1533:Number of answers 1487:root name servers 1406:load distribution 1375:Internet Explorer 1249:authority section 1033:primary/secondary 987:root name servers 806:beginning at the 795:and zero or more 783:Domain name space 666:Elizabeth Feinler 658:SRI International 600:An important and 520:unsolicited email 487:), IP addresses ( 440:network protocols 419:Internet Protocol 399: 398: 50:Application layer 16:(Redirected from 5337: 5289: 5287: 5285: 5276: 5266: 5264: 5262: 5243: 5232:"DNS Complexity" 4535: 4506: 4505: 4503: 4501: 4490: 4484: 4483: 4481: 4479: 4460: 4454: 4453: 4451: 4440: 4431: 4422: 4409: 4403: 4402: 4362: 4356: 4355: 4353: 4351: 4336: 4330: 4329: 4312: 4306: 4305: 4289: 4283: 4282: 4276: 4269: 4260: 4254: 4253: 4245: 4239: 4238: 4236: 4234: 4223: 4217: 4216: 4214: 4191: 4173: 4164: 4158: 4157: 4148: 4146:10.17487/RFC9250 4130: 4124: 4123: 4117: 4108: 4102: 4088: 4082: 4057: 4048: 4046:10.17487/RFC2136 4026: 4020: 4006: 3997: 3990: 3984: 3977: 3971: 3968: 3962: 3961: 3959: 3957: 3942: 3936: 3935: 3933: 3932: 3917: 3911: 3910: 3908: 3906: 3895: 3889: 3888: 3886: 3885: 3870: 3864: 3863: 3861: 3860: 3846: 3840: 3839: 3837: 3836: 3821: 3815: 3814: 3794: 3788: 3787: 3767: 3761: 3760: 3758: 3757: 3751:10.17487/RFC9499 3734: 3728: 3724: 3715: 3713:10.17487/RFC3696 3694: 3685: 3664: 3658: 3650: 3641: 3639:10.17487/RFC4343 3623: 3617: 3616: 3598: 3592: 3591: 3589: 3587: 3575: 3573:10.17487/RFC1034 3549: 3540: 3539: 3537: 3535: 3523: 3521:10.17487/RFC1034 3497: 3491: 3490: 3488: 3486: 3474: 3472:10.17487/RFC7719 3452: 3443: 3442: 3433: 3431:10.17487/RFC1034 3411: 3396: 3395: 3393: 3391: 3375: 3369: 3368: 3356: 3350: 3347: 3341: 3340: 3338: 3336: 3330:Internet Society 3321: 3315: 3314: 3312: 3311: 3297: 3291: 3290: 3288: 3287: 3278:. Archived from 3268: 3262: 3256: 3250: 3244: 3238: 3232: 3223: 3222: 3211: 3202: 3199: 3193: 3187: 3181: 3175: 3169: 3168: 3150: 3144: 3140: 3131: 3129:10.17487/RFC3467 3110: 3104: 3103: 3101: 3099: 3093: 3082: 3073: 3067: 3066: 3057: 3055:10.17487/RFC1035 3035: 3018: 3017: 3015: 3013: 3007: 2976: 2967: 2961: 2960: 2958: 2951: 2942: 2936: 2929: 2923: 2922: 2882: 2791:Domain hijacking 2769: 2764: 2763: 2658: 2498:and the numeral 2489: 2485: 2241: 2238: 2235: 2232: 2229: 2226: 2223: 2220: 2217: 2214: 2211: 2208: 2205: 2202: 2199: 2196: 2193: 2190: 2187: 2160: 2156: 2141:Wildcard records 1979: 1975: 1938:Resource records 1882: 1878: 1872:Question section 1831: 1826: 1821: 1816: 1808: 1662: 1658: 1549: 1545: 1475: 1474: 1468: 1463: 1462: 1452: 1451: 1445: 1440: 1439: 1362:Broken resolvers 1282:Negative caching 1261:top level domain 862:top-level domain 797:resource records 708:Paul Mockapetris 696:have the domain 595:e-mail addresses 583: 582: 571: 570: 560: 391: 384: 377: 39: 38: 21: 5345: 5344: 5340: 5339: 5338: 5336: 5335: 5334: 5305: 5304: 5283: 5281: 5274: 5260: 5258: 5226: 5171: 5163:DNS Terminology 5030: 4968: 4951: 4814: 4547: 4545:Standards track 4542: 4540:Further reading 4532: 4514: 4509: 4499: 4497: 4496:. VeriSign, Inc 4492: 4491: 4487: 4477: 4475: 4462: 4461: 4457: 4449: 4438: 4432: 4425: 4420:Wayback Machine 4410: 4406: 4363: 4359: 4349: 4347: 4338: 4337: 4333: 4314: 4313: 4309: 4290: 4286: 4274: 4267: 4261: 4257: 4246: 4242: 4232: 4230: 4225: 4224: 4220: 4212: 4171: 4165: 4161: 4131: 4127: 4115: 4109: 4105: 4089: 4085: 4027: 4023: 4007: 4000: 3991: 3987: 3978: 3974: 3969: 3965: 3955: 3953: 3944: 3943: 3939: 3930: 3928: 3919: 3918: 3914: 3904: 3902: 3896: 3892: 3883: 3881: 3872: 3871: 3867: 3858: 3856: 3848: 3847: 3843: 3834: 3832: 3823: 3822: 3818: 3811: 3795: 3791: 3784: 3768: 3764: 3755: 3753: 3735: 3731: 3695: 3688: 3652: 3651: 3624: 3620: 3613: 3599: 3595: 3585: 3583: 3550: 3543: 3533: 3531: 3498: 3494: 3484: 3482: 3458:DNS Terminology 3453: 3446: 3412: 3399: 3389: 3387: 3376: 3372: 3357: 3353: 3348: 3344: 3334: 3332: 3322: 3318: 3309: 3307: 3299: 3298: 3294: 3285: 3283: 3270: 3269: 3265: 3257: 3253: 3245: 3241: 3233: 3226: 3221:. 23 July 2012. 3213: 3212: 3205: 3200: 3196: 3188: 3184: 3176: 3172: 3165: 3151: 3147: 3111: 3107: 3097: 3095: 3091: 3080: 3074: 3070: 3036: 3021: 3011: 3009: 3005: 2974: 2968: 2964: 2956: 2949: 2945: 2943: 2939: 2930: 2926: 2883: 2879: 2875: 2870: 2767:Internet portal 2765: 2758: 2755: 2728:BigRock and PDR 2665: 2659: 2656: 2559:captive portals 2538: 2487: 2483: 2442: 2440:Security issues 2420: 2400: 2383: 2363: 2351: 2332: 2307: 2295: 2279: 2267: 2243: 2242: 2239: 2236: 2233: 2230: 2227: 2224: 2221: 2218: 2215: 2212: 2209: 2206: 2203: 2200: 2197: 2194: 2191: 2188: 2185: 2158: 2154: 2143: 1940: 1874: 1829: 1824: 1819: 1814: 1806: 1509: 1472: 1471: 1466: 1460: 1459: 1449: 1448: 1443: 1437: 1436: 1402:fault tolerance 1398:virtual hosting 1391: 1364: 1323: 1298: 1270: 1225: 1216:iterative query 1201:recursive query 1162: 1130: 1083: 1078: 1003: 971: 843: 785: 780: 650: 580: 579: 568: 567: 559:www.example.com 558: 547: 500:mail exchangers 395: 215:Transport layer 35: 28: 23: 22: 15: 12: 11: 5: 5343: 5333: 5332: 5327: 5322: 5317: 5303: 5302: 5296: 5290: 5267: 5244: 5225: 5224:External links 5222: 5221: 5220: 5210: 5200: 5190: 5170: 5167: 5166: 5165: 5155: 5145: 5135: 5125: 5115: 5105: 5095: 5085: 5075: 5065: 5055: 5045: 5029: 5026: 5025: 5024: 5013: 5002: 4991: 4980: 4967: 4964: 4963: 4962: 4950: 4947: 4946: 4945: 4935: 4925: 4915: 4905: 4895: 4885: 4875: 4865: 4855: 4845: 4835: 4825: 4813: 4810: 4809: 4808: 4798: 4788: 4778: 4768: 4758: 4748: 4738: 4728: 4718: 4708: 4698: 4688: 4678: 4668: 4658: 4648: 4638: 4628: 4618: 4608: 4598: 4588: 4578: 4568: 4558: 4546: 4543: 4541: 4538: 4537: 4536: 4530: 4513: 4510: 4508: 4507: 4485: 4455: 4423: 4404: 4357: 4331: 4307: 4298:Cisco Umbrella 4284: 4255: 4240: 4218: 4182:(2): 228–244. 4159: 4125: 4103: 4083: 4021: 3998: 3985: 3972: 3963: 3937: 3912: 3890: 3865: 3841: 3816: 3809: 3789: 3782: 3762: 3743:tools.ietf.org 3729: 3726:Informational. 3686: 3618: 3611: 3593: 3541: 3492: 3444: 3397: 3370: 3351: 3342: 3316: 3292: 3263: 3251: 3249:, p. 120. 3239: 3237:, p. 119. 3224: 3203: 3194: 3192:, p. 113. 3182: 3180:, p. 112. 3170: 3163: 3145: 3142:Informational. 3105: 3068: 3019: 2962: 2937: 2924: 2876: 2874: 2871: 2869: 2868: 2863: 2858: 2853: 2848: 2843: 2838: 2833: 2828: 2823: 2818: 2813: 2811:DNS over HTTPS 2808: 2803: 2798: 2793: 2788: 2783: 2778: 2772: 2771: 2770: 2754: 2751: 2664: 2661: 2654: 2625: 2624: 2623: 2622: 2611:DNS over HTTPS 2597: 2583: 2537: 2534: 2451:authentication 2447:data integrity 2441: 2438: 2419: 2416: 2399: 2396: 2382: 2379: 2362: 2359: 2354:DNS over HTTPS 2350: 2347: 2331: 2328: 2324:zone transfers 2306: 2303: 2294: 2291: 2278: 2275: 2266: 2263: 2210:*.a.x.example. 2184: 2151:asterisk label 2142: 2139: 2062: 2061: 2058: 2055: 2051: 2050: 2047: 2044: 2040: 2039: 2036: 2033: 2027: 2026: 2023: 2020: 2016: 2015: 2012: 2009: 2005: 2004: 2001: 1998: 1994: 1993: 1986: 1983: 1960:load balancing 1939: 1936: 1930: 1929: 1926: 1923: 1919: 1918: 1915: 1912: 1908: 1907: 1904: 1901: 1897: 1896: 1889: 1886: 1873: 1870: 1867: 1866: 1863: 1860: 1857: 1853: 1852: 1849: 1846: 1843: 1839: 1838: 1835: 1832: 1827: 1822: 1817: 1812: 1809: 1803: 1802: 1799: 1798:Transaction ID 1796: 1793: 1789: 1788: 1785: 1782: 1779: 1776: 1773: 1770: 1767: 1764: 1761: 1758: 1755: 1752: 1749: 1746: 1743: 1740: 1737: 1734: 1731: 1728: 1725: 1722: 1719: 1716: 1713: 1710: 1707: 1704: 1701: 1698: 1695: 1692: 1687: 1681: 1680: 1677: 1674: 1671: 1668: 1652: 1651: 1648: 1645: 1641: 1640: 1637: 1634: 1630: 1629: 1626: 1623: 1619: 1618: 1615: 1612: 1608: 1607: 1604: 1601: 1597: 1596: 1593: 1590: 1586: 1585: 1582: 1579: 1575: 1574: 1571: 1568: 1564: 1563: 1556: 1553: 1521:Identification 1508: 1505: 1479: 1478: 1455: 1390: 1387: 1363: 1360: 1339:e-mail clients 1322: 1319: 1297: 1296:Reverse lookup 1294: 1269: 1268:Record caching 1266: 1224: 1221: 1161: 1158: 1129: 1126: 1082: 1079: 1077: 1074: 1066:, to indicate 1002: 999: 970: 967: 842: 839: 784: 781: 779: 776: 724:In 1984, four 649: 646: 618:simultaneously 606:cloud services 546: 543: 474:address spaces 455:fault-tolerant 429:identification 397: 396: 394: 393: 386: 379: 371: 368: 367: 366: 365: 358: 353: 348: 343: 335: 334: 328: 327: 326: 325: 318: 313: 308: 303: 298: 288: 287: 286: 281: 268: 267: 265:Internet layer 261: 260: 259: 258: 251: 246: 241: 236: 231: 226: 218: 217: 211: 210: 209: 208: 201: 196: 191: 186: 181: 176: 171: 166: 161: 156: 151: 146: 141: 136: 131: 126: 121: 116: 111: 106: 101: 96: 91: 81: 76: 71: 61: 53: 52: 46: 45: 26: 9: 6: 4: 3: 2: 5342: 5331: 5328: 5326: 5323: 5321: 5318: 5316: 5313: 5312: 5310: 5300: 5299:Mess with DNS 5297: 5294: 5291: 5280: 5273: 5268: 5256: 5255: 5250: 5245: 5241: 5237: 5233: 5228: 5227: 5219: 5215: 5211: 5209: 5205: 5201: 5199: 5195: 5191: 5188: 5184: 5180: 5179: 5178: 5176: 5164: 5160: 5156: 5154: 5150: 5146: 5144: 5140: 5136: 5134: 5130: 5126: 5124: 5120: 5116: 5114: 5110: 5106: 5104: 5100: 5096: 5094: 5090: 5086: 5084: 5080: 5076: 5074: 5070: 5066: 5064: 5060: 5056: 5054: 5050: 5046: 5043: 5039: 5035: 5034: 5033: 5022: 5018: 5014: 5011: 5007: 5003: 5000: 4996: 4992: 4989: 4985: 4981: 4978: 4974: 4970: 4969: 4961: 4957: 4953: 4952: 4944: 4940: 4936: 4934: 4930: 4926: 4924: 4920: 4916: 4914: 4910: 4906: 4904: 4900: 4896: 4894: 4890: 4886: 4884: 4880: 4876: 4874: 4870: 4866: 4864: 4860: 4856: 4854: 4850: 4846: 4844: 4840: 4836: 4834: 4830: 4826: 4824: 4820: 4816: 4815: 4807: 4803: 4799: 4797: 4793: 4789: 4787: 4783: 4779: 4777: 4773: 4769: 4767: 4763: 4759: 4757: 4753: 4749: 4747: 4743: 4739: 4737: 4733: 4729: 4727: 4723: 4719: 4717: 4713: 4709: 4707: 4703: 4699: 4697: 4693: 4689: 4687: 4683: 4679: 4677: 4673: 4669: 4667: 4663: 4659: 4657: 4653: 4649: 4647: 4643: 4639: 4637: 4633: 4629: 4627: 4623: 4619: 4617: 4613: 4609: 4607: 4603: 4599: 4597: 4593: 4589: 4587: 4583: 4579: 4577: 4573: 4569: 4567: 4563: 4559: 4557: 4553: 4549: 4548: 4533: 4531:9780735211759 4527: 4523: 4522: 4516: 4515: 4495: 4489: 4473: 4469: 4465: 4459: 4448: 4444: 4437: 4430: 4428: 4421: 4417: 4414: 4408: 4400: 4396: 4392: 4388: 4384: 4380: 4376: 4372: 4368: 4361: 4345: 4341: 4335: 4327: 4323: 4322: 4317: 4311: 4303: 4299: 4295: 4288: 4281: 4273: 4266: 4259: 4251: 4244: 4228: 4222: 4211: 4207: 4203: 4199: 4195: 4190: 4185: 4181: 4177: 4170: 4163: 4155: 4152: 4147: 4142: 4138: 4137: 4129: 4122: 4114: 4107: 4100: 4096: 4092: 4087: 4080: 4076: 4072: 4068: 4064: 4060: 4055: 4052: 4047: 4042: 4038: 4037: 4032: 4025: 4018: 4014: 4010: 4005: 4003: 3995: 3989: 3982: 3976: 3967: 3951: 3947: 3941: 3926: 3922: 3916: 3901: 3894: 3879: 3875: 3869: 3855: 3851: 3845: 3830: 3826: 3820: 3812: 3806: 3802: 3801: 3793: 3785: 3779: 3775: 3774: 3766: 3752: 3748: 3744: 3740: 3733: 3727: 3722: 3719: 3714: 3709: 3705: 3704: 3699: 3693: 3691: 3683: 3679: 3675: 3671: 3667: 3662: 3656: 3648: 3645: 3640: 3635: 3631: 3630: 3622: 3614: 3608: 3604: 3597: 3582: 3579: 3574: 3569: 3565: 3561: 3560: 3555: 3548: 3546: 3530: 3527: 3522: 3517: 3513: 3509: 3508: 3503: 3496: 3481: 3478: 3473: 3468: 3464: 3460: 3459: 3451: 3449: 3440: 3437: 3432: 3427: 3423: 3419: 3418: 3410: 3408: 3406: 3404: 3402: 3385: 3381: 3374: 3366: 3362: 3355: 3346: 3331: 3327: 3320: 3306: 3302: 3296: 3281: 3277: 3273: 3267: 3260: 3255: 3248: 3243: 3236: 3231: 3229: 3220: 3216: 3210: 3208: 3198: 3191: 3186: 3179: 3174: 3166: 3160: 3156: 3149: 3143: 3138: 3135: 3130: 3125: 3121: 3120: 3115: 3109: 3090: 3086: 3079: 3072: 3064: 3061: 3056: 3051: 3047: 3043: 3042: 3034: 3032: 3030: 3028: 3026: 3024: 3004: 3000: 2996: 2992: 2988: 2984: 2980: 2973: 2966: 2955: 2948: 2941: 2934: 2928: 2920: 2916: 2912: 2908: 2904: 2900: 2896: 2892: 2888: 2881: 2877: 2867: 2864: 2862: 2859: 2857: 2854: 2852: 2849: 2847: 2844: 2842: 2839: 2837: 2834: 2832: 2831:Multicast DNS 2829: 2827: 2824: 2822: 2819: 2817: 2814: 2812: 2809: 2807: 2804: 2802: 2799: 2797: 2796:DNS hijacking 2794: 2792: 2789: 2787: 2784: 2782: 2779: 2777: 2774: 2773: 2768: 2762: 2757: 2750: 2748: 2744: 2739: 2738:exclusively. 2737: 2733: 2729: 2725: 2721: 2716: 2714: 2710: 2706: 2702: 2696: 2694: 2690: 2686: 2682: 2678: 2674: 2670: 2653: 2651: 2647: 2643: 2639: 2635: 2629: 2620: 2616: 2612: 2608: 2607: 2605: 2604:advertisement 2601: 2598: 2595: 2594:onion routing 2591: 2587: 2584: 2581: 2578: 2577: 2576: 2573: 2571: 2566: 2564: 2560: 2556: 2552: 2548: 2547:DNS hijacking 2544: 2533: 2531: 2526: 2524: 2519: 2517: 2513: 2509: 2505: 2501: 2497: 2493: 2480: 2478: 2474: 2470: 2466: 2461: 2459: 2454: 2452: 2448: 2437: 2434: 2429: 2425: 2415: 2413: 2409: 2405: 2395: 2392: 2388: 2378: 2376: 2372: 2368: 2358: 2355: 2346: 2344: 2340: 2336: 2327: 2325: 2321: 2317: 2312: 2309:UDP reserves 2302: 2300: 2290: 2288: 2283: 2274: 2272: 2262: 2260: 2256: 2252: 2248: 2182: 2180: 2176: 2172: 2168: 2164: 2152: 2148: 2138: 2136: 2132: 2128: 2123: 2121: 2117: 2113: 2109: 2104: 2101: 2097: 2095: 2091: 2087: 2083: 2079: 2075: 2071: 2068: 2059: 2056: 2053: 2052: 2048: 2045: 2042: 2041: 2037: 2034: 2032: 2029: 2028: 2024: 2021: 2018: 2017: 2013: 2010: 2007: 2006: 2002: 1999: 1996: 1995: 1991: 1987: 1984: 1981: 1980: 1974: 1972: 1967: 1965: 1961: 1957: 1953: 1949: 1945: 1935: 1927: 1924: 1921: 1920: 1916: 1913: 1910: 1909: 1905: 1902: 1899: 1898: 1894: 1890: 1887: 1884: 1883: 1877: 1858: 1855: 1854: 1844: 1841: 1840: 1828: 1823: 1818: 1813: 1805: 1804: 1790: 1786: 1783: 1780: 1777: 1774: 1771: 1768: 1765: 1762: 1759: 1756: 1753: 1750: 1747: 1744: 1741: 1738: 1735: 1732: 1729: 1726: 1723: 1720: 1717: 1714: 1711: 1708: 1705: 1702: 1699: 1696: 1693: 1691: 1688: 1686: 1683: 1682: 1667: 1663: 1657: 1649: 1646: 1643: 1642: 1638: 1635: 1632: 1631: 1627: 1624: 1621: 1620: 1616: 1613: 1610: 1609: 1605: 1602: 1599: 1598: 1594: 1591: 1588: 1587: 1583: 1580: 1577: 1576: 1572: 1569: 1566: 1565: 1561: 1557: 1554: 1551: 1550: 1544: 1542: 1538: 1534: 1530: 1526: 1522: 1517: 1515: 1504: 1502: 1498: 1494: 1492: 1488: 1483: 1476: 1464: 1456: 1453: 1441: 1433: 1432: 1431: 1430:For example: 1428: 1424: 1422: 1418: 1414: 1409: 1407: 1403: 1399: 1394: 1386: 1384: 1383:Google Chrome 1379: 1376: 1372: 1368: 1359: 1357: 1352: 1346: 1344: 1340: 1336: 1327: 1321:Client lookup 1318: 1316: 1310: 1308: 1303: 1293: 1291: 1287: 1283: 1278: 1274: 1265: 1262: 1257: 1252: 1250: 1246: 1242: 1238: 1233: 1231: 1220: 1217: 1212: 1210: 1206: 1202: 1197: 1195: 1191: 1187: 1182: 1180: 1176: 1175:non-recursive 1172: 1167: 1160:DNS resolvers 1157: 1155: 1151: 1148: 1146: 1145: 1138: 1136: 1125: 1123: 1118: 1116: 1111: 1105: 1103: 1095: 1090: 1086: 1073: 1070: 1069: 1065: 1061: 1057: 1053: 1049: 1048:authoritative 1044: 1041: 1039: 1034: 1030: 1029: 1024: 1020: 1015: 1012: 1008: 1007:authoritative 998: 996: 992: 988: 984: 980: 976: 966: 964: 962: 957: 953: 951: 945: 941: 937: 934:approved the 933: 928: 926: 922: 918: 914: 910: 906: 902: 898: 892: 888: 886: 882: 878: 874: 869: 867: 863: 858: 856: 852: 848: 838: 836: 828: 823: 819: 817: 813: 809: 805: 800: 798: 794: 790: 775: 773: 768: 766: 762: 758: 754: 750: 746: 742: 738: 734: 731: 727: 722: 720: 715: 713: 709: 703: 701: 700: 694: 690: 686: 681: 679: 675: 671: 667: 663: 659: 655: 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