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DNS Server

DNS Server

The Domain Name System (DNS) is a system that stores information associated with domain names in a distributed database on networks, such as the Internet. The domain name system associates many types of information with domain names, but most importantly, it provides the IP address associated with the domain name. It also lists mail exchange servers accepting e-mail for each domain. This means that DNS is involved with each page visit on the internet and with each email message sent. DNS is useful for several reasons. Most well known, the DNS makes it possible to attach hard-to-remember IP addresses (such as 207.142.131.206) to easy-to-remember domain names (such as "wikipedia.org") Humans take advantage of this when they recite URLs and e-mail addresses. Less recognized, the domain name system makes it possible for people to assign authoritative names, without needing to communicate with a central registrar each time.

A brief history of the DNS

The practice of using a name as a more human-legible abstraction of a machine's numerical address on the network predates even TCP/IP, all the way back to the ARPAnet era. Originally, each computer on the network retrieved a file called HOSTS.TXT from SRI (now SRI International) which mapped an address (eg. 192.0.2.135) to a name (eg. www.example.com.) The Hosts file still exists on most modern operating systems either by default or through configuration and allows users to specify an IP Address to use for a hostname without checking the DNS. This file is now used primarily for troubleshooting DNS errors or mapping local addresses to more organic names. Such a system had inherent limitations, because of the obvious requirement that every time a given computer's address changed, every computer that wanted to communicate with it would need an update to its Hosts file. The growth of networking called for a more scalable system: one which recorded a change in a host's address in one place only. Other hosts would learn about the change dynamically through a notification system, thus completing a globally accessible network of all hosts' names and their associated IP Addresses. Enter the DNS. Paul Mockapetris invented the DNS in 1983; the original specifications appear in RFC 882 and 883. In 1987, the publication of RFC 1034 and RFC 1035 updated the DNS specification and made RFC 882 and RFC 883 obsolete. Several more recent RFCs have proposed various extensions to the core DNS protocols.

How the DNS works in theory

Actors

1987 The domain name space is a gigantic tree of domain names. Each node or leaf in the tree is associated with resource records, which hold the information associated with the domain name. The tree is divided into zones. A zone is a collection of connected nodes that are authoritatively served by an authoritative DNS nameserver. (Note that a single nameserver can host several zones.) When a system administrator wants to let another administrator control a part of the domain name space within his or her zone of authority, he or she can delegate control to the other administrator. This splits a part of the old zone off into a new zone, which is served by the second administrator's nameservers. The old zone is no longer authoritative for what is under the authority of the new zone. The information associated with nodes is looked up by a resolver. A resolver knows how to communicate with name servers by sending DNS requests, and heeding DNS responses. Resolving usually entails recursing through several name servers to find the needed information. Some resolvers are simple, and can only communicate with a single name server. These simple resolvers rely on a recursing name server to perform the work of finding information for it.

Understanding the parts of a domain name

A domain name usually consists of two or more parts (technically labels), separated by dots. For example wikipedia.org.
- The rightmost label conveys the top-level domain (for example, the address en.wikipedia.org has the top-level domain org).
- Each label to the left specifies a subdivision or subdomain of the domain above it. Note that "subdomain" expresses relative dependence, not absolute dependence: for example, wikipedia.org comprises a subdomain of the org domain, and en.wikipedia.org could form a subdomain of the domain wikipedia.org (in practice, however, en.wikipedia.org actually represents a hostname). In theory, this subdivision can go down to 127 levels deep, and each label can contain up to 63 characters, as long as the whole domain name does not exceed a total length of 255 characters. But in practice some domain registries have shorter limits than that.
- Finally, the leftmost part of the domain name (usually) expresses the hostname. The rest of the domain name simply specifies a way of building a logical path to the information required; the hostname is the actual target system name for which an IP address is desired. For example, the domain name en.wikipedia.org has the hostname "en". The DNS consists of a hierarchical set of DNS servers. Each domain or subdomain has one or more authoritative DNS servers that publish information about that domain and the name servers of any domains "beneath" it. The hierarchy of authoritative DNS servers matches the hierarchy of domains. At the top of the hierarchy stand the root servers: the servers to query when looking up (resolving) a top-level domain name.

An example of theoretical DNS recursion

root servers An example may clarify this process. Suppose an application needs to find the IP address of www.wikipedia.org. It puts this question to a local DNS recursor.
- Before starting, the recursor has to know where to find the root servers; administrators of recursive DNS servers manually specify (and periodically update) a file called the root hints which specify recently known IP addresses of these servers, from which the DNS server can obtain a current complete list.
- The process starts by the recursor asking one of these root servers - for example, the server with the IP address "198.41.0.4" - the question "what is the IP address for www.wikipedia.org?"
- The root server replies with a delegation, meaning roughly: "I don't know the IP address of www.wikipedia.org, but I do know that the DNS server at 204.74.112.1 has information on the org domain."
- The local DNS recursor then asks that DNS server (i.e. 204.74.112.1) the same question it had previously put to the root servers, i.e. "what is the IP address for www.wikipedia.org?". It gets a similar reply - essentially, "I don't know the address of www.wikipedia.org, but I do know that the DNS server at 207.142.131.234 has information on the wikipedia.org domain."
- Finally the request goes to this third DNS server (207.142.131.234), which replies with the required IP address. This process utilises recursive searching.

Understanding domain registration and glue records

Reading the example above, you might reasonably wonder: "how does the DNS server 204.74.112.1 know what IP address to give out for the wikipedia.org domain?" In the first step of the process, we noted that a DNS recursor has the IP addresses of the root servers more-or-less hard coded. Equally, the name servers that are authoritative for the Top-Level Domains change very infrequently. However, the name servers that provide authoritative answers for common domain names may change relatively often. As part of the process of registering a domain name (and at any time thereafter), a registrant provides the registry with the name servers that will be authoritative for that domain name; therefore, when registering wikipedia.org, that domain is associated with the name servers gunther.bomis.com and zwinger.wikipedia.org at the .org registry. Consequently, in the example above, when the server identified by 204.74.112.1 receives a request, the DNS server scans its list of domains, locates wikipedia.org, and returns the name servers associated with that domain. Name servers in delegations are listed 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. Since this can introduce a bootstrapping problem when the name of the nameserver is in the domain about which nothing is yet known, it is occasionally necessary for the nameserver providing the delegation to also provide the IP address of the next nameserver. This record is called a glue record.

DNS in practice

When an application (such as a web browser) tries to find the IP address of a domain name, it doesn't necessarily follow all of the steps outlined in the Theory section above. We will first look at the concept of caching, then outline the operation of DNS in "the real world".

Caching and time to live

Because of the huge volume of requests generated by a system like the DNS, the designers wished to provide a mechanism to reduce the load on individual DNS servers. The mechanism devised provided that when a DNS resolver (i.e. client) received a DNS response, it would cache that response for a given period of time. A value (set by the administrator of the DNS server handing out the response) called the time to live, or TTL defines that period of time. Once a response goes into cache, the resolver will consult its cached (stored) answer; only when the TTL expires (or until an administrator manually flushes the response from the resolver's memory) will the resolver contact the DNS server for the same information. Generally, the time to live is specified in the Start of Authority (SOA) record. SOA parameters are:
- Serial — the zone serial number, incremented when the zone file is modified, so the slave and secondary name servers know when the zone has been changed and should be reloaded.
- Refresh — This is the number of seconds between update requests from secondary and slave name servers.
- Retry — This is the number of seconds the secondary or slave will wait before retrying when the last attempt has failed.
- Expire — This is the number of seconds before a master or slave will wait before considering the data stale if it cannot reach the primary name server.
- Minimum — Previously used to determine the minimum TTL, this is used for negative caching. (Newer versions of named will accept 'M','H','D' & 'W' suffixes indicating that the time interval is respectively in Minutes, Hours, Days and Weeks).

Caching time

An important consequence of this distributed and caching architecture is that changes to the DNS are not always immediately effective globally. This is best explained with an example: If an administrator has set a TTL of 6 hours for the host www.wikipedia.org, and then changes the IP address to which www.wikipedia.org resolves at 12:01pm, the administrator must consider that a person who cached a response with the old IP Address at 12:00pm will not consult the DNS server again until 6:00pm. The period between 12:01pm and 6:00pm in this example is called caching time, which is best defined as a period of time that begins when you make a change to a DNS record and ends after the maximum amount of time specified by the TTL expires. This essentially leads to an important logistical consideration when making changes to the DNS: not everyone is necessarily seeing the same thing you're seeing. [http://www.ietf.org/rfc/rfc1537.txt RFC1537] helps to convey basic rules for how to set the TTL. Note that the term "propagation", although very widely used, is a poor term to describe the effects of caching. Specifically, it implies that [1] when you make a DNS change, it somehow spreads to all other DNS servers (instead, other DNS servers check in with yours as needed), and [2] that you do not have control over the amount of time the record is cached (you have complete control for all DNS records on your domain, except your NS records and any authoritative DNS servers that use your domain name). Many people incorrectly refer to a mysterious 48 hour or 72 hour propagation time when you make a DNS change. When you change the NS records for your domain or the IP addresses for hostnames of authoritative DNS servers using your domain (if any), there can be a lengthy period of time before all DNS servers use the new information. This is because those records are handled by the zone parent DNS servers (for example, the .com DNS servers if your domain is example.com), which typically cache those records for 48 hours. However, those DNS changes will be immediately available for any DNS servers that do not have them cached. And, any DNS changes on your domain other than the NS records and authoritative DNS server names can be nearly instantaneous, if you choose for them to be (by lowering the TTL once or twice ahead of time, and waiting until the old TTL expires before making the change).

DNS in the real world

TTL Users generally do not communicate directly with a DNS resolver. Instead DNS resolution is handled transparently via client applications such as web browsers (Mozilla Firefox, Safari, Opera, Internet Explorer, etc), mail clients (Outlook Express, Mozilla Thunderbird, etc), and other internet applications. When a request is made which necessitates a DNS lookup, such programs send a resolution request to the local DNS resolver in the operating system which in turn handles the communications required. 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 request to a designated DNS server or 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 configure that server's address manually or allow DHCP to set it; however, where systems administrators have configured systems to use their own DNS servers, their DNS resolvers will generally point to their own nameservers. This name server will then follow the process outlined above in DNS in theory, 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. As a final level of complexity, some applications such as Web browsers also have their own DNS cache, in order to reduce use of the DNS resolver library itself, which can add extra difficulty to DNS debugging, as it obscures which data is fresh, or lies in which cache. These caches typically have very short caching times of the order of 1 minute. A notable exception is Internet Explorer. Recent versions cache DNS records for 30 minutes[http://support.microsoft.com/default.aspx?scid=KB;en-us;263558].

Other DNS applications

The system outlined above provides a somewhat simplified scenario. The DNS includes several other functions:
- Hostnames and IP addresses do not necessarily match on a one-to-one basis. Many hostnames may correspond to a single IP address: combined with virtual hosting, this allows a single machine to serve many web sites. Alternatively a single hostname may correspond to many IP addresses: this can facilitate fault tolerance and load distribution, and also allows a site to move physical location seamlessly.
- There are many uses of DNS besides translating names to IP addresses. For instance, Mail transfer agents use DNS to find out where to deliver e-mail for a particular address. The domain to mail exchanger mapping provided by MX records accommodates another layer of fault tolerance and load distribution on top of the name to IP address mapping.
- Sender Policy Framework controversially takes advantage of a DNS record type, the TXT record.
- To provide resilience in the event of computer failure, multiple DNS servers provide coverage of each domain. In particular, thirteen root servers exist worldwide. DNS programs or operating systems have the IP addresses of these servers built in. The USA hosts, at least nominally, all but three of the root servers. However, because many root servers actually implement anycast, where many different computers can share the same IP address to deliver a single service over a large geographic region, most of the physical (rather than nominal) root servers now operate outside the USA. The DNS uses TCP and UDP on port 53 to serve requests. Almost all DNS queries consist of a single UDP request from the client followed by a single UDP reply from the server. TCP typically comes into play only when the response data size exceeds 512 bytes, or for such tasks as zone transfer.

Standards

- RFC 1034 Domain Names - Concepts and Facilities.
- RFC 1035 Domain Names - Implementation and Specification.
- RFC 1183 New DNS RR Definitions
- RFC 1706 DNS NSAP Resource Records
- RFC 1876 Location Information in the DNS (LOC)
- RFC 1886 DNS Extensions to support IP version 6
- RFC 1912 Common DNS Operational and Configuration Errors
- 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 2317 Classless IN-ADDR.ARPA delegation
- RFC 2672 Non-Terminal DNS Name Redirection
- RFC 2782 A DNS RR for specifying the location of services (DNS SRV)
- RFC 2845 Secret Key Transaction Authentication for DNS (TSIG)
- RFC 2874 DNS Extensions to Support IPv6 Address Aggregation and Renumbering
- RFC 3403 Dynamic Delegation Discovery System (DDDS) (NAPTR records)

Types of DNS records

Important categories of data stored in the DNS include the following:
- An A record or address record maps a hostname to a 32-bit IPv4 address.
- An AAAA record or IPv6 address record maps a hostname to a 128-bit IPv6 address.
- A CNAME record or canonical name record makes one domain name an alias of another. The aliased domain gets all the subdomains and DNS records of the original.
- An MX record or mail exchange record maps a domain name to a list of mail exchange servers for that domain.
- A PTR record or pointer record maps an IPv4 address to the canonical name for that host. Setting up a PTR record for a hostname in the in-addr.arpa domain that corresponds to an IP address implements reverse DNS lookup for that address. For example (at the time of writing), www.icann.net has the IP address 192.0.34.164, but a PTR record maps 164.34.0.192.in-addr.arpa to its canonical name, referrals.icann.org.
- An NS record or name server record maps a domain name to a list of DNS servers authoritative for that domain. Delegations depend on NS records.
- An SOA record or start of authority record specifies the DNS server providing authoritative information about an Internet domain, the email of the domain administrator, the domain serial number, and several timers relating to refreshing the zone.
- An SRV record is a generalized service location record.
- A TXT record allows an administrator to insert arbitrary text into a DNS record. For example, this record is used to implement the Sender Policy Framework specification. Other types of records simply provide information (for example, a LOC record gives the physical location of a host), or experimental data (for example, a WKS record gives a list of servers offering some well-known service such as HTTP or POP3 for a domain).

Internationalised domain names

Domain names must use only a subset of ASCII characters—the Roman alphabet in upper and lower case, the digits 0 through 9, and the hyphen. This prevented the representation of names and words of many languages natively. ICANN has approved the Punycode-based IDNA system, which maps Unicode strings into the valid DNS character set, as a workaround to this issue. Some registries have adopted IDNA.

DNS software

Various flavors of DNS software implement the DNS, including:
- BIND (Berkeley Internet Name Daemon) – full featured, most popular, de facto Internet standard
- djbdns (Daniel J. Bernstein's DNS) – composed of several small-footprint components
- MaraDNS – UDP only
- VitalQIP (Lucent Technologies)
- Adonis DNS Management Appliance (BlueCat Networks Inc)
- NSD (Name Server Daemon) – small footprint, UDP only, authoritative only
- PowerDNS
- Microsoft DNS (in the server editions of Windows 2000 and Windows 2003)
- Simple DNS Plus (JH Software) - shareware, runs on Windows DNS-oriented utilities include:
- dig (the "domain information groper")
- mysqlBind - BIND 8/9 DNS server administration system for one or hundreds of DNS servers. GPL licensed.

Legal users of domains

Registrant

No one in the world really "owns" a domain name except the Network Information Centre (NIC), or domain name registry. Most of the NICs in the world receive an annual fee from a legal user in order for the legal user to utilise the domain name (i.e. a sort of a leasing agreement exists, subject to the registry's terms and conditions). Depending on the various naming convention of the registries, legal users become commonly known as "registrants" or as "domain holders". ICANN holds a complete list of domain registries in the world. One can find the legal user of a domain name by looking in the WHOIS database held by most domain registries. For most of the more than 240 country code top-level domains (ccTLDs), the domain registries hold the authoritative WHOIS (Registrant, name servers, expiry dates etc). For instance, DENIC, Germany NIC holds the authoritative WHOIS to a .DE domain name. However, some domain registries, such as VeriSign, use a registry-registrar model. There are hundreds of Domain Name Registrars that actually perform the domain name registration with the end-user, such as eNom. By using this method of distribution, the registry only has to manage the relationship with the registrar, and the registrar maintains the relationship with the end-users, or 'registrants'. For .COM, .NET domain names, the domain registries, VeriSign holds a basic WHOIS (registrar and name servers etc). One can find the detailed WHOIS (Registrant, name servers, expiry dates etc) at the registrars. Since about 2001, most gTLD registries (.ORG, .BIZ, .INFO) have adopted a so-called "thick" registry approach, i.e. keeping the authoritative WHOIS with the various registries instead of the registrars.

Administrative contact

A registrant usually designates an administrative contact to manage the domain name. In practice, the administrative contact usually has the most immediate power over a domain. Management functions delegated to the administrative contacts may include (for example):
- the obligation to conform to the requirements of the domain registry in order to retain the right to use a domain name
- authorisation to update the physical address, e-mail address and telephone number etc in WHOIS

Technical contact

A technical contact manages the name servers of a domain name. The many functions of a technical contact include:
- making sure the configurations of the domain name conforms to the requirements of the domain registry
- updating the domain zone
- providing the 24x7 functionality of the name servers (that leads to the accessibility of the domain name)

Billing contact

Self-explanatory, the party whom a NIC invoices.

Name servers

Namely the authoritative name servers that host the domain name zone of a domain name.

Politics

Many investigators have voiced criticism of the methods used currently to control ownership of domains. Most commonly, critics claim abuse by monopolies or near-monopolies, such as VeriSign, Inc., and problems with assignment of top-level domains. The international body ICANN (the Internet Corporation for Assigned Names and Numbers) oversees the domain name industry.

Truth in Domain Names Act

In the United States, the "Truth in Domain Names Act", in combination with the PROTECT Act, forbids the use of a misleading domain name with the intention of attracting people into viewing a visual depiction of sexually explicit conduct on the internet

External links and documentation

- [http://www.linux.ie/articles/dns.php All About DNS]
- [http://www.linux.ie/articles/tutorials/dns-tsig.php Securing DNS with Transaction Signatures]
- [http://www.nap.edu/execsumm_pdf/11258.pdf Signposts in Cyberspace: The Domain Name System and Internet Navigation (PDF format)]
- [http://cr.yp.to/djbdns/forgery.html DNS Forgery]
- [http://ketil.froyn.name/poison.html DNS Poisoning, a practical example]
- [http://www.windowsnetworking.com/articles_tutorials/Quickly-Test-DNS-Resolution.html How to 'Quickly' Test DNS Resolution]
- [http://www.ckdhr.com/dns-loc/sites.html Sites supporting DNS LOC]
- [http://www.bind9.net/dns-links Domain Name System Links, Whitepapers, and Research]
- [http://www.dnswatch.info DNS lookups] shows recursive search process during dns lookup
- [http://www.adminschoice.com/docs/domain_name_service.htm Setting up DNS server in unix]
- [http://www.DNSstuff.com Online DNS tools]
- [http://support.microsoft.com/default.aspx?scid=KB;en-us;263558 Microsoft KB Article on IE Cache Times]
- [http://pdos.csail.mit.edu/chord/papers/ddns.pdf Serving DNS using a Peer-to-Peer Lookup Service]
- [http://distributeddns.sourceforge.net/ Distributed DNS] Category:Internet standards Category:Internet protocols ko:DNS ms:Sistem Nama Domain ja:Domain Name System

Domain name

The term domain name has multiple meanings, all related to the Domain Name System (main article).
- a name that is entered into a computer (e.g. as part of a website or other URL, or an email address) and then looked up in the global [Domain Name System] which informs the computer of the IP address(es) with that name.
- the product that registrars provide to their customers.
- a name looked up in the DNS for other purposes. They are sometimes colloquially (and incorrectly) referred to by marketers as "web addresses". Domain names are Hostnames that provide rememberable names to stand in for numeric IP addresses. They allow for any service to move to a different location in the topology of the Internet (or another internet), which would then have a different IP address. Each string of letters, digits and hyphens between the dots is called a label in the parlance of the domain name system (DNS). Valid labels are subject to certain rules, which have relaxed over the course of time. Originally labels must start with a letter, and end with a letter or digit; any intervening characters may be letters, digits, or hyphens. Labels must be between 1 and 63 characters long (inclusive). Letters are ASCII A–Z and a–z; domain names are compared case-insensitively. Later it became permissible for labels to commence with a digit (but not for domain names to be entirely numeric), and for labels to contain internal underscores, but support for such domain names is uneven. These are the rules imposed by the way names are looked up ("resolved") by DNS. Some top level domains (see below) impose more rules, such as a longer minimum length, on some labels. Fully qualified names (FQDNs) are sometimes written with a final dot. Translating numeric addresses to alphabetical ones, domain names allow Internet users to localize and visit websites. Additionally since more than one IP address can be assigned to a domain name, and more than one domain name assigned to an IP address, one server can have multiple roles, and one role can be spread among multiple servers. One IP address can even be assigned to several servers, such as with anycast and hijacked IP space.

Examples

The following examples illustrates the difference between a URL (Uniform Resource Locator) and a domain name: : URL: http://www.example.com/ : Domain name: www.example.com As a general rule, the IP address and the server name are interchangeable. For most internet services, the server will not have any way to know which was used. However, the explosion of interest in the web means that there are far more websites than servers. To accommodate this, the hypertext transfer protocol (HTTP) specifies that the client tells the server which name is being used. This way, one server with one IP address can provide different sites for different domain names. This feature is goes under the name virtual hosting and is commonly used by web hosts. For example, the server at 192.0.34.166 handles all of the following sites: : www.example.com : www.example.net : www.example.org

Top-level domains

Every domain name ends in a top-level domain (TLD) name, which is always either one of a small list of generic names (three or more characters), or a two characters territory code based on ISO-3166 (there are few exceptions and new codes are integrated case by case). Examples of (gTLD) extensions are:
- .com
- .net
- .org
- .biz
- .info
- .name
- .museum
- .travel
- .pro
- .aero
- .xxx (disapproved by ICANN) Examples of country code top-level domain (ccTLD) extensions are:
- .au
- .eu (not an ISO-3166 code, and not a country, but used anyway for the European Union. Scheduled to be launched December 7, 2005)
- .us
- .uk (not an ISO-3166 code, but used anyway)
- .br
- .fr
- .es
- .de
- .in
- .it
- .jp
- .ca
- .nz
- .su (not an existing country at the moment - Soviet Union, but used anyway)

Official assignment

ICANN (Internet Corporation for Assigned Names and Numbers) has overall responsibility for managing the DNS. It controls the root domain, delegating control over each top-level domain to a domain name registry. For ccTLDs, the domain registry is typically controlled by the government of that country. ICANN has a consultation role in these domain registries but is in no position to regulate the terms and conditions of how a domain name is allocated or who allocates it in each of these country level domain registries. On the other hand, generic top-level domains (gTLDs) are governed directly under ICANN which means all terms and conditions are defined by ICANN with the cooperation of the gTLD registries. Domain names which are theoretically leased can be considered in the same way as real estate, due to a significant impact on online brand building, advertising, search engine optimization, etc.

Uses and abuses

As domain names became attractive to marketers, rather than just the technical audience for which they were originally intended, they began to be used in manners that in many cases did not fit in their intended structure. As originally planned, the structure of domain names followed a strict hierarchy in which the top level domain indicated the type of organization (commercial, governmental, etc.), and addresses would be nested down to third, fourth, or further levels to express complex structures, where, for instance, branches, departments, and subsidiaries of a parent organization would have addresses which were subdomains of the parent domain. Also, hostnames were intended to correspond to actual physical machines on the network, generally with only one name per machine. However, once the World Wide Web became popular, site operators frequently wished to have memorable addresses, regardless of whether they fit properly in the structure; thus, since the .com domain was the most popular and memorable, even noncommercial sites would often get addresses under it, and sites of all sorts wished to have second-level domain registrations even if they were parts of a larger entity where a logical subdomain would have made sense (e.g., abcnews.com instead of news.abc.com). A website found at http://www.example.org will often be advertised without the "http://", and in most cases can be reached by just typing "example.org" into a web browser. In the case of a .com, the website can sometimes be reached by just typing "example" (depending on browser versions and configuration settings, which vary in how they interpret incomplete addresses). With "virtual hosting", often many domain names would point to the same physical server. The popularity of domain names also led to uses which were regarded as abusive by established companies with trademark rights; this was known as cybersquatting, in which somebody took a name that resembled a trademark in order to profit from traffic to that address. To combat this, various laws and policies were enacted to allow abusive registrations to be forcibly transferred, but these were sometimes themselves abused by overzealous companies committing reverse domain hijacking against domain users who had legitimate grounds to hold their names, such as their being generic words as well as trademarks in a particular context, or their use in the context of fan or protest sites with free speech rights of their own.

Generic domain names — problems arising out of unregulated name selection

Within a particular top-level domain, parties are generally free to select an unallocated domain name as their own on a first come, first served basis. For generic or commonly used names, this may sometimes lead to the use of a domain name which is inaccurate or misleading. This problem can be seen with regard to the ownership or control of domain names for a generic product or service. By way of illustration, there has been tremendous growth in the number and size of literary festivals around the world in recent years. In this context, currently a generic domain name such as literary.org is available to the first literary festival organisation which is able to obtain registration, even if the festival in question is very young or obscure. Some critics would argue that there is greater amenity in reserving such domain names for the use of, for example, a regional or umbrella grouping of festivals. Related issues may also arise in relation to non-commercial domain names.

Unconventional domain names

Due to the rarity of one-word dot-com domain names, many unconventional domain names, domain hacks, have been gaining popularity. They make use of the top-level domain as an integral part of the website's title. Two of the most visited domain hack websites are del.icio.us and blo.gs, which spell out 'delicious' and 'blogs', respectively. Some unconventional domain names are also used to create email hacks. Non-working examples that spell 'James' are j@m.es and j@mes.com, which use the domain names m.es (of Spain's .es) and mes.com.

Commercial resale of domain names

An economic effect of the widespread usage of domain names has been the resale market for generic domain names that has sprung up in the last decade. Certain domains, especially those related to business, gambling, pornography, and other commercially lucrative fields have become very much in demand to corporations and entrepreneurs due to their intrinsic value in attracting clients. In fact, the most expensive internet domain name to date, according to Guinness World Records, is business.com which was resold in 1999 for $7.5 million. Another high value domain name, sex.com, was stolen from its rightful owner by means of a forged transfer instruction via fax. During the height of the dot-com era, the domain was earning millions of dollars per month in advertising revenue from the large influx of visitors that arrived daily. Two long-running US lawsuits resulted, one against the thief and one against the domain registrar VeriSign[http://www.wired.com/news/business/0,1367,63142,00.html]. In one of the cases, the judge found in favor of the plaintiff, leading to an unprecendented ruling that classified domain names as property, granting them the same legal protections. In 1999, Microsoft traded the valuable name Bob.com for the name Windows2000.com which was the name of their new operating system.[http://www.theregister.com/1999/11/11/windows2000_com_owner_sells_domain/] One of the reasons for the value of domain names is that even without advertising or marketing, they attract clients seeking services and products who simply type in the generic name. Furthermore, generic domain names such as Rent.com or Books.com are extremely easy for potential customers to remember, increasing the probability that they become repeat customers or regular clients. Although the current domain market is nowhere as strong as it was during the dot-com heyday, it remains strong and is currently experiencing solid growth again. Annually tens of millions of dollars change hands due to the resale of domains. Large numbers of registered domain names lapse and are deleted each year. On average 25,000 domain names drop (are deleted) every day.

Caveat Emptor

Care should always be exercised when registering a domain name: DNS is case-insensitive and the modern trend of words run together with intercapping can be misinterpreted when converted to lowercase. Who Represents, a database of artists and agents, chose http://www.whorepresents.com; Experts Exchange, the programmers' site, famously had http://www.expertsexchange.com; Pen Island unwisely chose http://www.penisland.net; a therapists' network thought http://www.therapistfinder.com looked good and of course the Italian power company PowerGen Italia became http://www.powergenitalia.com. Fortunately the dash is allowable in DNS, a fact possibly unknown to those organisations listed above. DNS is case-insensitive, so CAMFT's website can be advertised as http://www.TherapistFinder.com (instead of http://www.therapistfinder.com).

External links

- [http://www.dnjournal.com/ Domain Name Journal] - Covering the Domain Name Industry with Profiles and News.
- [http://www.domainnamewire.com/ Domain Name Wire] - Latest news about Domain Name Industry, domain sales, and legal issues.
- [http://www.gobin.info/domainname/ Domain Name Universe] - List of all existing Domain Name Registries, global Domain Name Search, Latest news.
- [http://www.faqs.org/rfcs/std/std13.html STD 13/RFC 1034], Domain Names—Concepts and Facilities, an Internet Protocol Standard.
- [http://www.icann.org/ ICANN] - Internet Corporation for Assigned Names and Numbers.
- [http://www.icann.org/udrp/udrp.htm UDRP], Uniform Domain-Name Dispute-Resolution Policy.
- [http://www.internic.net/ Internic.net], public information regarding Internet domain name registration services.
- [http://lifeofawebsite.com/begin/country-specific-domains.php List of Country Specific Domains]
- [http://www.circleid.com/ CircleID], Community discussions on TLDs and Internet infrastructure.
- [http://xona.com/domainhacks/ Domain Hacks] - unconventional domain name search utility
- The authoritative definition is that given in
- RFC 1032 - Domain administrators guide
- RFC 1033 - Domain administrators operations guide
- RFC 1034 - Domain names - concepts and facilities
- RFC 1035 - Domain names - implementation and specification Category:Domain Name System Category:Internet Category:Information technology Category:Identifiers als:Domäne (Internet) ja:ドメイン名

Internet

:For the more general networking concept, see internetworking. The Internet, or simply the Net, is the worldwide system of interconnected computer networks which makes information stored on it accessible. This information is transmitted by packet switching using a standardized Internet Protocol (IP) and many other protocols. It is made up of thousands of smaller commercial, academic, domestic and government networks. It carries various information and services, such as electronic mail, online chat, and the interlinked web pages and other documents of the World Wide Web.

Creation of the Internet

During the 1950s, several communications researchers realized that there was a need to allow general communication between users of various computers and communications networks. This led to research into decentralized networks, queuing theory, and packet switching. The subsequent creation of ARPANET in the United States in turn catalyzed a wave of technical developments that made it the basis for the development of the Internet. Contrary to popular myth, the DoD did not create the ARPANET so that they could communicate to the US Government after a nuclear war. The first TCP/IP wide area network was operational in 1984 when the United States' National Science Foundation (NSF) constructed a university network backbone that would later become the NSFNet. It was then followed by the opening of the network to commercial interests in 1995. Important separate networks that offered gateways into, then later merged into the Internet include Usenet, Bitnet and the various commercial and educational X.25 networks such as Compuserve and JANET. The ability of TCP/IP to work over these pre-existing communication networks allowed for a great ease of growth. Use of Internet as a phrase to describe a single global TCP/IP network originated around this time. The collective network gained a public face in the 1990s. In August 1991 CERN in Switzerland publicized the new World Wide Web project, two years after Tim Berners-Lee had begun creating HTML, HTTP and the first few web pages at CERN in Switzerland. In 1993 the Mosaic web browser version 1.0 was released, and by late 1994 there was growing public interest in the previously academic/technical Internet. By 1996 the word "Internet" was common public currency, but it referred almost entirely to the World Wide Web. Meanwhile, over the course of the decade, the Internet successfully accommodated the majority of previously existing public computer networks (although some networks such as FidoNet have remained separate). This growth is often attributed to the lack of central administration, which allows organic growth of the network, as well as the non-proprietary open nature of the Internet protocols, which encourages vendor interoperability and prevents any one company from exerting too much control over the network.

Today's Internet

FidoNets, FTP client, and Telnet client]] Apart from the complex physical connections that make up its infrastructure, the Internet is held together by bi- or multi-lateral commercial contracts (for example peering agreements) and by technical specifications or protocols that describe how to exchange data over the network. Indeed, the Internet is essentially defined by its interconnections and routing policies. In an often-cited, if perhaps gratuitously mathematical definition, Seth Breidbart once described the Internet as "the largest equivalence class in the reflexive, transitive, symmetric closure of the relationship 'can be reached by an IP packet from'". Unlike older communications systems, the Internet protocol suite was deliberately designed to be independent of the underlying physical medium. Any communications network, wired or wireless, that can carry two-way digital data can carry Internet traffic. Thus, Internet packets flow through wired networks like copper wire, coaxial cable, and fiber optic; and through wireless networks like Wi-Fi. Together, all these networks, sharing the same high-level protocols, form the Internet. The Internet protocols originate from discussions within the Internet Engineering Task Force (IETF) and its working groups, which are open to public participation and review. These committees produce documents that are known as Request for Comments documents (RFCs). Some RFCs are raised to the status of Internet Standard by the Internet Architecture Board (IAB). Some of the most used protocols in the Internet protocol suite are IP, TCP, UDP, DNS, PPP, SLIP, ICMP, POP3, IMAP, SMTP, HTTP, HTTPS, SSH, Telnet, FTP, LDAP, SSL, and TLS. Some of the popular services on the Internet that make use of these protocols are e-mail, Usenet newsgroups, file sharing, Instant Messenger, the World Wide Web, Gopher, session access, WAIS, finger, IRC, MUDs, and MUSHs. Of these, e-mail and the World Wide Web are clearly the most used, and many other services are built upon them, such as mailing lists and blogs. The Internet makes it possible to provide real-time services such as Internet radio and webcasts that can be accessed from anywhere in the world. Some other popular services of the Internet were not created this way, but were originally based on proprietary systems. These include IRC, ICQ, AIM, and Gnutella. There have been many analyses of the Internet and its structure. For example, it has been determined that the Internet IP routing structure and hypertext links of the World Wide Web are examples of scale-free networks. Similar to how the commercial Internet providers connect via Internet exchange points, research networks tend to interconnect into large subnetworks such as:
- GEANT
- Internet2
- GLORIAD These in turn are built around relatively smaller networks. See also the list of academic computer network organizations In network schematic diagrams, the Internet is often represented by a cloud symbol, into and out of which network communications can pass.

Internet culture

The Internet is also having a profound impact on work, leisure, knowledge and worldviews. worldviews]]

ICANN

The Internet Corporation for Assigned Names and Numbers (ICANN) is the authority that coordinates the assignment of unique identifiers on the Internet, including domain names, Internet protocol addresses, and protocol port and parameter numbers. A globally unified namespace (i.e., a system of names in which there is one and only one holder of each name) is essential for the Internet to function. ICANN is headquartered in Marina del Rey, California, but is overseen by an international board of directors drawn from across the Internet technical, business, academic, and non-commercial communities. The US government continues to have a privileged role in approving changes to the root zone file that lies at the heart of the domain name system. Because the Internet is a distributed network comprising many voluntarily interconnected networks, the Internet, as such, has no governing body. ICANN's role in coordinating the assignment of unique identifiers distinguishes it as perhaps the only central coordinating body on the global Internet, but the scope of its authority extends only to the Internet's systems of domain names, Internet protocol addresses, and protocol port and parameter numbers.

The World Wide Web

Through keyword-driven Internet research using search engines like Google, millions worldwide have easy, instant access to a vast and diverse amount of online information. Compared to encyclopedias and traditional libraries, the World Wide Web has enabled a sudden and extreme decentralization of information and data. Some companies and individuals have adopted the use of 'weblogs' or blogs, which are largely used as easily-updatable online diaries. Some commercial organizations encourage staff to fill them with advice on their areas of specialization in the hope that visitors will be impressed by the expert knowledge and free information, and be attracted to the corporation as a result. One example of this practice is Microsoft, via whose product developers publish their personal blogs in order to pique the public's interest in their work. For more information on the distinction between the World Wide Web and the Internet itself — as in everyday use the two are sometimes confused — see Dark internet where this is discussed in more detail.

Remote access

The Internet allows computer users to connect to other computers and information stores easily, wherever they may be across the world. They may do this with or without the use of security, authentication and encryption technologies, depending on the requirements. This is encouraging new ways of working from home, collaboration and information sharing in many industries. An accountant sitting at home can audit the books of a company based in another country, on a server situated in a third country that is remotely maintained by IT specialists in a fourth. These accounts could have been created by home-working book-keepers, in other remote locations, based on information e-mailed to them from offices all over the world. Some of these things were possible before the widespread use of the Internet, but the cost of private, leased lines would have made many of them infeasible in practice. An office worker away from his or her desk, perhaps the other side of the world on a business trip or a holiday, can open a remote desktop session into his or her normal office PC using a secure Virtual Private Network (VPN) connection via the Internet. This gives him or her complete access to all their normal files and data, including e-mail and other applications, while they are away.

Collaboration

This low-cost and nearly instantaneous sharing of ideas, knowledge and skills has revolutionized some, and given rise to whole new, areas of human activity. One example of this is the collaborative development and distribution of Free/Libre/Open-Source Software (FLOSS) such as Linux, Mozilla and OpenOffice.org. See Collaborative software.

File-sharing

A computer file can be e-mailed to customers, colleagues and friends as an attachment. It can be uploaded to a website or FTP server for easy download by others. It can be put into a "shared location" or onto a file server for instant use by colleagues. The load of bulk downloads to many users can be eased by the use of "mirror" servers or peer-to-peer networking. In any of these cases, access to the file may be controlled by user authentication; the transit of the file over the Internet may be obscured by encryption and money may change hands before or after access to the file is given. The price can be paid by the remote charging of funds from, for example a credit card whose details are also passed - hopefully fully encrypted - across the Internet. The origin and authenticity of the file received may be checked by digital signatures or by MD5 message digests. These simple features of the Internet, over a world-wide basis, are changing the basis for the production, sale and distribution of many types of product, wherever they can be reduced to a computer file for transmission. This includes all manner of office documents, publications, software products, music, photography, video, animations, graphics and the other arts. This in turn is causing seismic shifts in each of the existing industry associations, such as the RIAA and MPAA, that previously controlled the production and distribution of these products.

Streaming media and VoIP

Many existing radio and television broadcasters have provided Internet 'feeds' of their live audio and video streams (for example, the BBC). They have been joined by a range of pure Internet 'broadcasters' who never had on-air licences. This means that an Internet-connected device, such as a computer or something more specific, can be used to access on-line media in much the same way as was previously possible only with a TV or radio receiver. The range of material is much wider, from pornography to highly specialised technical web-casts. The simplest equipment can allow anybody, with little censorship or licencing control, to broadcast on a worldwide basis. Time-shift viewing or listening is not a problem as the BBC have shown with their Preview, Classic Clips and Listen Again features. Web-cams can be seen as an even lower-budget extension of this phenomenon. In this case the picture may update only slowly - perhaps once every few seconds or slower, but Internet users can watch animals around an African waterhole, ships in the Panama Canal or the traffic at a local roundabout live and in real time. Video chat rooms, video conferencing, and remote controllable webcams have become popular. Some people install webcams in their bedrooms that can be accessed by other voyeurs, often with two-way sound. VoIP stands for Voice over IP, where IP refers to the Internet Protocol that underlies all Internet communication. This phenomenon began as an optional two-way voice extension to some of the Instant Messaging systems that took off around the turn of the millennium. In recent years many people and organizations have made VoIP systems as easy to use and as convenient as a normal telephone. The benefit is that, as the actual voice traffic is carried by the Internet, VoIP is free or costs much less than an actual telephone call, especially over long distances and especially for those with always-on ADSL or DSL Internet connections anyway. The disadvantages are that it is still difficult to initiate a call with someone, unless they also have a VoIP phone or are at their computer and that there are still several competing standards that are mitigating against universal acceptance. In all of these cases, existing large organisations, that have grown accustomed to regular incomes for their services, are finding increased competition in their service areas, coming directly from the Internet. While newcomers strive to make these inroads, the traditional industries are having to adapt, adopt, complain or suffer. Meanwhile the consumer in each case most probably benefits from the increased range of services and possible price reductions. Some worry about censorship and control while others see a continuing globalisation of culture and norms.

Language

Main article: English on the Internet The most prevalent language for communication on the Internet is English. This may be due to the Internet's origins or to the growing role of English as an international language. It may also be related to the poor capability of early computers to handle characters other than those in the basic Latin alphabet (see Unicode). After English (32 % of web visitors) the most-requested languages on the world wide web are Chinese 13 %, Japanese 8 %, Spanish 6 %, German 6 % and French 4 %. (From [http://www.internetworldstats.com/stats7.htm Internet World Stats]) By continent, 33 % of the world's Internet users are based in Asia, 29 % in Europe and 23 % in North America.[http://www.internetworldstats.com/stats.htm] The Internet's technologies have developed enough in recent years that good facilities are available for development and communication in most widely used languages. However, some glitches such as mojibake still remain.

Cultural awareness

From a cultural awareness perspective, the Internet has been both an advantage and a liability. For people who are interested in other cultures it provides a significant amount of information and an interactivity that would be unavailable otherwise. However, for people who are not interested in other cultures there is some evidence indicating that the Internet enables them to avoid contact to a greater degree than ever before.

Censorship

Some countries, such as Iran and the People's Republic of China, restrict what people in their countries can see on the Internet, especially unwanted political and religious content. In the Western world, it is Germany that has the highest rate of censorship. Internet Service Providers are required by law to block some sites that contain child pornography or Nazi or Islamist propaganda. Censorship is sometimes done through government sponsored censoring filters, or by means of law or culture, making the propagation of targeted materials extremely hard. At the moment most Internet content is available regardless of where one is in the world, so long as one has the means of connecting to it.

Internet access

Germany Common methods of home access include dial-up, landline broadband (over coaxial cable, fiber optic or copper wires), Wi-Fi, satellite and cell phones. Public places to use the Internet include libraries and Internet cafes, where computers with Internet connections are available. There are also Internet access points in many public places like airport halls, in some cases just for brief use while standing. Various terms are used, such as "public Internet kiosk", "public access terminal", and "Web payphone". Many hotels now also have public terminals, though these are usually fee based. Wi-Fi provides wireless access to computer networks, and therefore can do so to the Internet itself. Hotspots providing such access include Wi-Fi-cafes, where a would-be user needs to bring their own wireless-enabled devices such as a laptop or PDA. These services may be free to all, free to customers only, or fee-based. A hotspot need not be limited to a confined location. The whole campus or park, or even the entire city can be enabled. Grassroots efforts have led to wireless community networks. Apart from Wi-Fi, there have been experiments with proprietary mobile wireless networks like Ricochet, various high-speed data services over cellular or mobile phone networks, and fixed wireless services. These services have not enjoyed widespread success due to their high cost of deployment, which is passed on to users in high usage fees. New wireless technologies such as WiMAX have the potential to alleviate these concerns and enable simple and cost effective deployment of metropolitan area networks covering large, urban areas. There is a growing trend towards wireless mesh networks, which offer a decentralized and redundant infrastructure and are often considered the future of the Internet. Broadband access over power lines was approved in 2004 in the United States in the face of stiff resistance from the amateur radio community. The problem with modulating a carrier signal onto power lines is that an above-ground power line can act as a giant antenna and jam long-distance radio frequencies used by amateurs, seafarers and others. Countries where Internet access is available to a majority of the population include Germany, India, China, Chile, Iceland, Finland, Sweden, Greece, Italy, Australia, Denmark, the United States, Canada, the United Kingdom, The Netherlands, Japan, Singapore, Taiwan, Thailand, South Korea and Norway. The use of the Internet around the world has been growing rapidly over the last decade, although the growth rate seems to have slowed somewhat after 2000. The phase of rapid growth is ending in industrialized countries, as usage becomes ubiquitous there, but the spread continues in Africa, Latin America, the Caribbean and the Middle East. However, there are still problems for many. ADSL and other broadband access are rare or nonexistent in most developing countries. Even in developed countries, high prices, mediocre performance and access restrictions often limit its uptake. Within individual countries, wide differences may exist between larger cities (often having multiple providers of broadband access) and some rural areas, where no broadband access may be available at all. The expansion of the availability of Internet access is a way to bridge the so-called digital divide.

Capitalization conventions

In formal usage, Internet is traditionally written with a capital first letter. The Internet Society, the Internet Engineering Task Force, the Internet Corporation for Assigned Names and Numbers, the World Wide Web Consortium, and several other Internet-related organizations all use this convention in their publications. In English grammar, proper nouns are capitalized. Most newspapers, newswires, periodicals, and technical journals also capitalize the term. Examples include the New York Times, the Associated Press, Time, The Times of India, Hindustan Times and Communications of the ACM. In other cases, the first letter is often written small (internet), and many people are not aware of any convention of using a capital letter. Some argue that internet is the correct form. Since 2000, a significant number of publications have switched to using internet. Among them are The Economist, the Financial Times, the London Times, and the Sydney Morning Herald. As of 2005, most publications using internet appear to be located outside of North America although one American news source, Wired News, has adopted the lowercase spelling.

Leisure

The Internet has been a major source of leisure since before the World Wide Web, with entertaining social experiments such as MOOs being conducted on university servers, and humor-related USENET groups receiving much of the main traffic. Today, many Internet forums have sections devoted to neta; short cartoons in the form of Flash movies are also popular. The pornography and gambling industries have both taken full advantage of the World Wide Web, and often provide a significant source of advertising revenue for other Web sites. Although many governments have attempted to put restrictions on both industries' use of the Internet, this has generally failed to stop their widespread popularity. One main area of leisure on the Internet is multiplayer gaming. This form of leisure creates communities, bringing people of all ages and origins to enjoy the fast-paced world of multiplayer games. These range from MMORPG to first-person shooters, from role-playing games to online gambling. This has revolutionized the way many people interact and spend their free time on the Internet. Online gaming began with services such as GameSpy and MPlayer, which players of games would typically subscribe to. Non-subscribers were limited to certain types of gameplay or certain games. With the release of Diablo by Blizzard Entertainment, gamers were treated to a built in online game service that was free of charge. With Blizzard's next game, StarCraft, the gaming world saw an explosion in the numbers of players using the Internet to play multi-player games. StarCraft may have been the first non-MMO game in which most players utilized the online gameplay as opposed to the single-player gameplay. Online gaming has progressed so much in the last 10 years that gamers earn a living from being a professional at the subject by winning tournaments and prizes as well as signing sponsor deals. Because there is a large support for certain online games, a new community has been born for people modding games, where users edit games to add a whole new element to it. This is how games such as Counter-Strike were born from the Half-Life Gaming Engine. Cyberslacking has become a serious drain on corporate resources; the average UK employee spends 57 minutes a day surfing, according to a study by Peninsula Business Services[http://news.scotsman.com/topics.cfm?tid=914&id=1001802003].

A complex system

Many computer scientists see the Internet as a "prime example of a large-scale, highly engineered, yet highly complex system" (Willinger, et al). The Internet is extremely heterogeneous. (For instance, data transfer rates and physical characteristics of connections vary widely.) The Internet exhibits "emergent phenomena" that depend on its large-scale organization. For example, data transfer rates exhibit temporal self-similarity.

Marketing

The Internet has also become a big market, and the biggest companies today have grown by taking advantage of the efficient low-cost advertising and commerce through the Internet. It is the fastest way to spread information to a vast community of people all at once. The Internet has revolutionized shopping –– a person can order a CD online and receive it in the mail within a couple of days, or download it directly in some cases.

Criticism

Many hyperlinks are outdated as time takes its toll on the existence of URL weblinks. These weblinks are often times defunct and are retained as hyperlinks for extended timeframes as a result of laziness or being busy enough to be sidetracked away from updating webpages. This is a common hoax for people who are fans in the field of what those links provide them with/to.

External links

General

- [http://www.channel101.com/ Internet TV Stations]
- [http://www.isoc.org/ The Internet Society (ISOC)]
- [http://www.techterms.org/internet.php Internet Dictionary] - Definitions of Internet-related terms
- [http://www.experienced-people.co.uk/1099-webmaster-glossary/ The Alternate Internet Glossary] (Humor)
- A [http://www.illusivecreations.com Calgary Web Design] company that has put together over 300 articles about the internet and web development. You can view them by going [http://www.illusivecreations.com/articles/ here].
- [http://www.clickz.com/stats/sectors/geographics/article.php/5911_151151 Internet access stats]
- [http://www.sharpened.net/glossary/ Glossary of Computer and Internet Terms]
- [http://scoreboard.keynote.com/scoreboard/Main.aspx?Login=Y&Username=public&Password=public Internet Health Report] from Keynote
- [http://www.internetworldstats.com/stats.htm Internet World Stats]

Articles

- [http://www.iht.com/articles/2005/09/29/business/net.php "EU and U.S. clash over control of the Net" - International Herald Tribune article by Tom Wright]
- [http://www.wired.com/wired/archive/13.08/intro.html "10 Years that changed the world" - WiReD looks back at the evolution of the Internet over last 10 years]
- [http://www.fourmilab.ch/documents/digital-imprimatur/ John Walker: The Digital Imprimatur]
- [http://www.addressingtheworld.info addressingtheworld.info] - website accompanying a book (ISBN 0742528103) on the history of DNS
- [http://computer.howstuffworks.com/internet-infrastructure.htm How Stuff Works explanation of the Infrastructure of the Internet]
- [http://www.searchandgo.com/articles/internet/net-explained-1.php Internet Explained] Seven part article explaining the origins to the present and a future look at the Internet.
- [http://www.wired.com/news/culture/0,1284,64596,00.html?tw=wn_tophead_7 "It's Just the 'internet' Now" - Wired.com article by Tony Long]

History

- [http://www.isoc.org/internet/history/brief.shtml The Internet Society History Page]
- [http://www.internetvalley.com/archives/mirrors/cerf-how-inet.txt How the Internet Came to Be]
- [http://www.zakon.org/robert/internet/timeline/ Hobbes' Internet Timeline v7.0]
- [http://www.ciolek.com/PAPERS/e-scholarship2000.html Futures and Non-futures for Scholarly Internet. ]
- [http://www.lk.cs.ucla.edu/internet_history.html History of the Internet links]
- [http://www.ietf.org/rfc/rfc801.txt RFC 801, planning the TCP/IP switchover]
- [http://www.archive.org/ Internet Archive] - A searchable database of old cached versions of websites dating back to 1996
- A list of lectures, some of which relate to the Internet, from the Massachusetts Institute of Technology is available [http://ocw.mit.edu/OcwWeb/Comparative-Media-Studies/CMS-930Media--Education--and-the-MarketplaceFall2001/VideoLectures/index.htm here]. Of particular interest is lecture #3 The Next Big Thing: Video Internet which is delivered in Real Player format. The lecture gives a brief history of networking; discusses convergence between the internet/telephone/television networks; the expansion of broadband access; makes predictions about the future of delivery of video over the internet.

References

- Walter Willinger, Ramesh Govindan, Sugih Jamin, Vern Paxson, and Scott Shenker. (2002). Scaling phenomena in the Internet. In Proceedings of the National Academy of Sciences, 99, suppl. 1, 2573 – 2580. Category:Communication Category:Digital media Category:Internet Category:Digital Revolution Category:Technology Category:Computer networks Category:Networks ko:인터넷 ms:Internet ja:インターネット simple:Internet th:อินเทอร์เน็ต fiu-vro:Internet

IP address

An IP address (Internet Protocol address) is a unique number that devices use in order to identify and communicate with each other on a network utilizing the Internet Protocol standard. Any participating device — including routers, computers, time-servers, internet FAX machines, and some telephones — must have its own unique address. This allows information passed onwards on behalf of the sender to indicate where to send it next, and for the receiver of the information to know that it is the intended destination. The numbers currently used in IP addresses range from 0.0.0.0 to 255.255.255.255, though some of these values are reserved for specific purposes. This does not provide enough possibilities for every internet device to have its own permanent number. Subnet routing, Network Address Translation and the Dynamic Host Configuration Protocol (DHCP) server all allow local networks to use the same IP addresses as other networks elsewhere though both are connected to the Internet. Devices such as network printers, web servers and email servers are often allocated static IP addresses so they can always be found. IP addresses are conceptually similar to phone numbers, except they are used in LANs (Local Area Network), WANs (Wide Area Network), and the Internet. Because the numbers are not easy for humans to remember, the Domain Name System provides a service analogous to an address book lookup called "domain name resolution" or "name resolution". Special DNS servers on the internet are dedicated to performing the translation from a domain name to an IP address and v.v.

More detail

The Internet Protocol (IP) knows each logical host interface by a number, the IP address. On any given network, this number must be unique among all the host interfaces that communicate through this network. Users of the Internet are sometimes given a host name in addition to their numerical IP address by their Internet service provider. The IP addresses of users browsing the world wide web are used to enable communications with the server of the web site. Also, it is usually in the header of email messages one sends. In fact, for all programs that utilize the TCP/IP protocol, the sender IP address and destination IP address are required in order to establish communications and send data. Depending on one's Internet connection the IP address can be the same every time one connects (called a static IP address), or different every time one connects, (called a dynamic IP address). In order to use a dynamic IP address, there must exist a server which can provide the address. IP addresses are usually given out through a server service called DHCP or the Dynamic Host Configuration Protocol. If a static address is used, it must be manually programmed into parameters of the device's network interface. Internet addresses are needed not only for unique enumeration of hosted interfaces, but also for routing purposes, therefore a high fraction of them are always unused or reserved. The unique nature of IP addresses makes it possible in many situations to track which computer — and by extension, which person — has sent a message or engaged in some other activity on the Internet. This information has been used by law enforcement authorities to identify criminal suspects. The dynamically-assigned nature of many IP addresses can make this even more difficult.

IP version 4

Addressing

In version 4 of the Internet protocol (IPv4), the current standard protocol for the Internet, IP addresses consist of 32 bits, which makes for 4,294,967,296 (over 4 billion) unique host interface addresses in theory. In practice, because addresses are allocated in blocks, many unused addresses are unavailable (much like unused phone numbers in a sparsely-populated area code), so that there is some pressure to extend the address range via IP version 6 (see below). IPv4 addresses are commonly expressed as a dotted quad, four octets (8 bits) separated by periods. The host known as www.wikipedia.org currently has the number 3482223596, written as 207.142.131.236 in base-256: 3482223596 equals 207×256³ + 142×256² + 131×256¹ + 236×256⁰. (Resolving the name "www.wikipedia.org" to its associated number is handled by Domain Name System servers.) IPv4 addresses were originally divided into two parts: the network and the host. A later change increased that to three parts: the network, the subnetwork, and the host, in that order. However, with the advent of classless inter-domain routing (CIDR), this distinction is no longer meaningful, and the address can have an arbitrary number of levels of hierarchy. (Technically, this was already true any time after the advent of subnets, since a site could elect to have more than one level of subnetting inside a network number.) For more information on current IPv4 address ranges, see tables on class ranges and special (reserved) ranges. See also: Classful network

Assignment

Each interface of a device is assigned, at least conceptionally, a unique IP address. In practice, some interfaces may be unnumbered, and many addresses are not globally unique. The actual assignment of an address is not arbitrary. The fundamental principle of routing, that addresses encode information about a device's location within a network, implies that an address assigned to one part of a network will not function in another part of the network. A hierarchical structure, standardized by CIDR and overseen by the Internet Assigned Numbers Authority (IANA) and its Regional Internet Registries (RIRs), manages the assignment of Internet address worldwide. Each RIR maintains a publically searchable WHOIS database that provides information about IP address assignments; information from these databases plays a central role in numerous tools which attempt to locate IP addresses geographically. (See List of assigned Class A IP addresses for a list of some of the large Class A address blocks currently assigned.)

Exhaustion

Some private IP address space has been allocated via RFC 1918. This means the addresses are available for any use by anyone and therefore the same RFC 1918 IP addresses can be reused. However they are not routable on the Internet. They are used extensively due to the shortage of registerable addresses. Network address translation (NAT) is required to connect those networks to the Internet. While a number of measures have been taken to conserve the limited existing IPv4 address space (such as the use of NAT and Private Addressing), the number of 32-bit IP addresses is not sufficient to accommodate the long-term growth of the Internet. For this reason, the plan is that the Internet 128-bit IPv6 addressing scheme will be adopted over the next 5 to 15 years. See also: IPv4 address exhaustion

IP version 5

What would be considered IPv5 existed only as an experimental non-IP real time streaming protocol called ST2, described in RFC 1819. This protocol was abandoned; RSVP has replaced it to some degree.

IP version 6

In IPv6, the new (but not yet widely deployed) standard protocol for the Internet, addresses are 128 bits wide, which, even with generous assignment of netblocks, should suffice for the foreseeable future. In theory, there would be exactly 2¹²⁸, or about 3.403 × 10³⁸ unique host interface addresses. If the earth were made entirely out of 1 cubic millimeter grains of sand, then you could give a unique address to each grain in 300 million planets the size of the earth. This large address space will be sparsely populated, which makes it possible to again encode more routing information into the addresses themselves.

Addressing

A version 6 address is written as eight 4-digit hexadecimal numbers separated by colons. For readability, addresses may be shortened in two ways. Within each colon-delimited section, leading zeroes may be truncated. Secondly, one string of zeroes (and only one) may be replaced with two colons (::). For example, all of the following addresses are equivalent:
- 1080:0000:0000:0000:0000:0034:0000:417A
- 1080:0:0:0:0:34:0:417A
- 1080::34:0:417A Global unicast IPv6 addresses are constructed as two parts: a 64-bit routing part followed by a 64-bit host identifier. Netblocks are specified as in the modern alternative for IPv4: network number, followed by a slash, and the number of relevant bits of the network number (in decimal). Example: 12AB::CD30:0:0:0:0/60 includes all addresses starting with 12AB00000000CD3. IPv6 has many improvements over IPv4 other than just bigger address space, including autorenumbering and mandatory support for IPsec. Further reading: Internet RFCs including RFC 791, RFC 1519 (IPv4 addresses), and RFC 2373 (IPv6 addresses).

External links

- [http://www.linuxjournal.com/article/7856 Introduction to geolocation by IP address]
- [http://www.circleid.com/community/topics/view/IP%20Addressing/ Articles on CircleID about IP addressing]
- [http://www.securityfocus.com/infocus/1674 IP Spoofing: An Introduction]
- [http://www.byte.com/art/9602/sec16/art4.htm IP-Address Management on LANs] - article in Byte magazine
- [http://www.circleid.com/posts/ip_address_allocation_vs_internet_production_i_understanding_the_relationsh/ Introduction to IP address allocation]
- [http://seeyourip.info/ IP-Address: detailed text description]
- [http://www.hostip.info/ Community project to geotarget IP addresses] Category:Computing Category:Computer networks Category:Information technology Category:Internet architecture Category:Identifiers als:IP-Adresse ko:IP 주소 ja:IPアドレス simple:IP address th:หมายเลขไอพี

Mail exchange server

A mail transfer agent or MTA (also called a mail server, or a mail exchange server in the context of the Domain Name System) is a computer program or software agent that transfers electronic mail messages from one computer to another. It receives messages from another MTA (relaying), a mail submission agent (MSA) that itself got the mail from a mail user agent (MUA), or directly from an MUA, thus acting as an MSA itself. The MTA works behind the scenes, while the user usually interacts with the MUA. The delivery of email to a user's mailbox typically takes place via a mail delivery agent (MDA); many MTAs have basic MDA functionality built in, but a dedicated MDA like procmail can provide more sophistication.

External links

- Daniel J. Bernstein, [http://cr.yp.to/surveys/smtpsoftware6.txt Internet host SMTP server survey], November 2001
- [http://www.geocities.com/mailsoftware42/ Open source Mail Server Comparison] Category:Email Category:Mail transport agents ja:メール転送エージェント th:เมลเซิร์ฟเวอร์

Uniform Resource Locator

A Uniform Resource Locator, URL (properly pronounced as a spelled-out initialism, not syllabized as 'earl'), or Web address, is a standardized address name layout for resources (such as documents or images) on the Internet (or elsewhere). First created by Tim Berners-Lee for use on the World Wide Web, the currently used forms are detailed by Internet standard RFC 1738. It is also known as Universal Resource Locator [http://www.orafaq.com/glossary/faqglosu.htm],[http://www.patrickgavin.com/SEO-Glossary.htm],[http://www.wda.org/Public/help/glossary.htm]. The URL was a fundamental innovation in the history of the Internet. The syntax is designed to be generic, extensible, and able to express addresses in any character set using a limited subset of ASCII characters (for instance, whitespace is never used in a URL). URLs are classified by the "scheme" which typically identifies the network protocol used to retrieve the resource over a computer network.

Definition

URIs and URLs

Every URL is a type of Uniform Resource Identifier (URI), or more precisely the set of URLs is a proper subset of the set of URIs. A URI identifies a particular resource while a URL both identifies a resource and indicates how to locate it. To illustrate the distinction consider the URI urn:ietf:rfc:1738 which identifies IETF RFC 1738 without indicating where to find the text of this RFC. Now consider three URLs for three separate documents containing the text of this RFC:
- http://www.ietf.org/rfc/rfc1738.txt
- http://www.w3.org/Addressing/rfc1738.txt
- http://rfc.sunsite.dk/rfc/rfc1738.html Each URL uniquely identifies each document and thus is a URI itself, but URL syntax is such that the identity allows one to also locate each of these documents. Thus, a URL functions as the document's address. Historically, the terms have been almost synonymous as almost all URIs have also been URLs. For this reason, many definitions in this article mention URIs instead of URLs; the discussion applies to both URIs and URLs.

URL scheme

A URL begins with the name of its scheme, followed by a colon, followed by a scheme-specific part. Some examples of URL schemes:
- http - HTTP resources
- https - HTTP over SSL
- ftp - File Transfer Protocol
- mailto - E-mail address
- ldap - Lightweight Directory Access Protocol lookups
- file - resources available on the local computer or over a local file sharing network
- news - Usenet newsgroups
- gopher - the Gopher protocol
- telnet - the telnet protocol
- data - the Data: URL scheme for inserting small pieces of content in place See also http://www.iana.org/assignments/uri-schemes

Generic URI syntax

The syntax of the scheme-specific part depends on the requirements of the scheme. Schemes using typical connection-based protocols use a common "generic URI" syntax, defined below: scheme://authority/path?query The authority typically consists of a hostname or IP address of a server, optionally followed by a colon and a port number. It may in fact also contain information on username and password for authenticating to the server. The path is a specification of a location in some hierarchical structure, using a slash ("/") as delimiter between components. The query part is typically intended to express parameters of a dynamic query to some database residing on the server.

Example: HTTP URLs

The URLs employed by HTTP, the protocol used to transmit web pages, are the most popular kind of URI and can be used as an example to demonstrate the concept of the URI. The HTTP URL syntax is: scheme://host:port/path?parameter=value#anchor
- scheme, in the case of HTTP, is most of the time http, but https can also be used for signifying HTTP over a TLS connection (to make the connection more secure).
- Many web browsers allow use of scheme://username:password@host:port/... for HTTP authentication. This format has been used as an exploit to make it difficult to correctly identify the server involved. Consequently, support for this format has been dropped from some browsers. According to section 3.3 of RFC 1738, "No user name or password is allowed" in HTTP URLs.
- host, which is probably the most prominent part of a URL, is in almost all cases the domain name of a server, e.g. www.wikipedia.org, google.com, www.imv.au.dk, etc.
- The :port portion specifies an IP port number. It is usually omitted (defaults to 80 in that case) and in the entire URL probably has the least relevance for the user.
- The path portion is used by the server (specified by host) in whatever way the server's software is set up, but in many cases it specifies a filename, possibly prepended with directory names. For example, in the path /wiki/Cow, wiki would be a (pseudo-)directory and Cow would be a (pseudo-)filename.
- The part given above as ?parameter=value is referred to as query portion (sometimes search portion). It can either be omitted, have one parameter-value pair as in the example, or have many of them, which is expressed as ?para=value&anotherpara=value&.... The parameter-value pairs are only relevant if the file specified by the path is not a simple, static webpage, but some sort of automatically generated page. The generator software uses the parameter-value pairs in any way it is set up; mostly they carry information specific to one user and one moment in the use of the site, like concrete search terms, usernames, etc. (Watch, for example, how the URL in your browser's address bar behaves during a [http://google.com/ Google] search: your search term is passed to some sophisticated program on google.com as a parameter, and Google's program returns a page with the search results to you.)
- The #anchor part, lastly, is called fragment identifier and refers to certain significant places inside a page; for example, this Wikipedia page has anchors at each section heading which can be referred to via the fragment ID. They are relevant if a URL should be given which, when loaded in a browser, directly jumps to a certain point in a long page. An example would be this link, which leads to this page and to the beginning of this section. (Watch how the URL in your browser's address bar changes when clicking the link.) For another example of a HTTP URL, see below.

URI references

The term URI reference means a particular instance of a URI, or portion thereof, as used in, for instance, an HTML document, in order to refer to a particular resource. A URI reference often looks just like a URL or the tail end of a URL. URI references introduce two new concepts: the distinction between absolute and relative references, and the concept of a fragment identifier. An absolute URL is a URI reference that is just like a URL defined above; it starts with a scheme followed by a colon and then a scheme-specific part. A relative URL is a URI reference that comprises just the scheme-specific part of a URL, or some trailing component thereof. The scheme and leading components are inferred from the context in which the URL reference appears: the base URI (or base URL) of the document containing the reference. A URI reference can also be followed by a hash sign ("#") and a pointer to within the resource referenced by the URI as a whole. This is not a part of the URI as such, but is intended for the "user agent" (browser) to interpret afte