The domain name space

The domain name space consists of a tree of domain names. Each node or leaf in the tree has zero or more resource records, which hold information associated with the domain name. The tree sub-divides into zones beginning at the root zone. A DNS zone consists of a collection of connected nodes authoritatively served by an authoritative nameserver. (Note that a single nameserver can host several zones.)

Administrative responsibility over any zone may be divided, thereby creating additional zones. Authority is said to be delegated for a portion of the old space, usually in form of sub-domains, to another nameserver and administrative entity. The old zone ceases to be authoritative for the new zone.

Parts of a domain name:

A domain name usually consists of two or more parts (technically labels), which are conventionally written separated by dots, such as example.com.

• The rightmost label conveys the top-level domain (for example, the address www.example.com has the top-level domain com).
• Each label to the left specifies a subdivision, or subdomain of the domain above it. Note: “subdomain” expresses relative dependence, not absolute dependence. For example: example.com is a subdomain of the com domain, and www.example.com is a subdomain of the domain example.com. In theory, this subdivision can go down 127 levels. Each label can contain up to 63 octets. The whole domain name may not exceed a total length of 253 octets. ^[5] In practice, some domain registries may have shorter limits.
• A hostname refers to a domain name that has one or more associated IP addresses; ie: the 'www.example.com' and 'example.com' domains are both hostnames, however, the 'com' domain is not.

DNS servers:

The Domain Name System is maintained by a distributed database system, which uses the client-server model. The nodes of this database are the name servers. Each domain or subdomain has one or more authoritative DNS servers that publish information about that domain and the name servers of any domains subordinate to it. The top of the hierarchy is served by the root nameservers: the servers to query when looking up (resolving) a top-level domain name (TLD).

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Domain Name System

The Domain Name System (DNS) is a hierarchical naming system for computers, services, or any resource participating in the Internet. It associates various information with domain names assigned to such participants. Most importantly, it translates domain names meaningful to humans into the numerical (binary) identifiers associated with networking equipment for the purpose of locating and addressing these devices world-wide. An often used analogy to explain the Domain Name System is that it serves as the "phone book" for the Internet by translating human-friendly computer hostnames into IP addresses. For example, www.example.com translates to 208.77.188.166.

The Domain Name System makes it possible to assign domain names to groups of Internet users in a meaningful way, independent of each user's physical location. Because of this, World-Wide Web (WWW) hyperlinks and Internet contact information can remain consistent and constant even if the current Internet routing arrangements change or the participant uses a mobile device. Internet domain names are easier to remember than IP addresses such as 208.77.188.166 (IPv4) or 2001:db8:1f70::999:de8:7648:6e8 (IPv6). People take advantage of this when they recite meaningful URLs and e-mail addresses without having to know how the machine will actually locate them.

The Domain Name System distributes the responsibility of assigning domain names and mapping those names to IP addresses by designating authoritative name servers for each domain. Authoritative name servers are assigned to be responsible for their particular domains, and in turn can assign other authoritative name servers for their sub-domains. This mechanism has made the DNS distributed, fault tolerant, and helped avoid the need for a single central register to be continually consulted and updated.

In general, the Domain Name System also stores other types of information, such as the list of mail servers that accept email for a given Internet domain. By providing a world-wide, distributed keyword-based redirection service, the Domain Name System is an essential component of the functionality of the Internet.

Other identifiers such as RFID tags, UPC codes, International characters in email addresses and host names, and a variety of other identifiers could all potentially utilize DNS

The Domain Name System also defines the technical underpinnings of the functionality of this database service. For this purpose it defines the DNS protocol, a detailed specification of the data structures and communication exchanges used in DNS, as part of the Internet Protocol Suite (TCP/IP). The context of the DNS within the Internet protocols may be seen in the following diagram. The DNS protocol was developed and defined in the early 1980s and published by the Internet Engineering Task Force

Server operating systems

Some popular operating systems for servers — such as FreeBSD, Solaris, and Linux — are derived from or are similar to UNIX. UNIX was originally a minicomputer operating system, and as servers gradually replaced traditional minicomputers, UNIX was a logical and efficient choice of operating system for the servers. UNIX-based operating systems, many of which are free in both senses, are popular.

Server-oriented operating systems tend to have certain features in common that make them more suitable for the server environment, such as

• GUI not available or optional,
• ability to reconfigure and update both hardware and software to some extent without restart,
• advanced backup facilities to permit regular and frequent online backups of critical data,
• transparent data transfer between different volumes or devices,
• flexible and advanced networking capabilities,
• automation capabilities such as daemons in UNIX and services in Windows, and
• tight system security, with advanced user, resource, data, and memory protection.

Server-oriented operating systems can in many cases interact with hardware sensors to detect conditions such as overheating, processor and disk failure, and consequently alert an operator and/or take remedial measures itself.

Because servers must supply a restricted range of services to perhaps many users while a desktop computer must carry out a wide range of functions required by its user, the requirements of an operating system for a server are different from those of a desktop machine. While it is possible for an operating system to make a machine both provide services and respond quickly to the requirements of a user, it is usual to use different operating systems on servers and desktop machines. Some operating systems are supplied in both server and desktop versions with similar user interface.

The desktop versions of the Windows and Mac OS X operating systems are deployed on a minority of servers, as are some proprietary mainframe operating systems, such as z/OS. The dominant operating systems among servers are UNIX-based and open source kernel distributions.

The rise of the microprocessor-based server was facilitated by the development of Unix to run on the x86 microprocessor architecture. The Microsoft Windows family of operating systems also runs on x86 hardware, and since Windows NT have been available in versions suitable for server use.

While the role of server and desktop operating systems remains distinct, improvements in the reliability of both hardware and operating systems have blurred the distinction between the two classes. Today, many desktop and server operating systems share similar code bases, differing mostly in configuration. The shift towards web applications and middleware platforms has also lessened the demand for specialist application servers.1

Server hardware

Hardware requirements for servers vary, depending on the server application. Absolute CPU speed is not usually as critical to a server as it is to a desktop machine. Servers' duties to provide service to many users over a network lead to different requirements like fast network connections and high I/O throughput. Since servers are usually accessed over a network they may run in headless mode without a monitor or input device. Processes which are not needed for the server's function are not used. Many servers do not have a graphical user interface (GUI) as it is unnecessary and consumes resources that could be allocated elsewhere. Similarly, audio and USB interfaces may be omitted.

Servers often run for long periods without interruption and availability must often be very high, making hardware reliability and durability extremely important. Although servers can be built from commodity computer parts, mission-critical servers use specialized hardware with low failure rates in order to maximize uptime. For example, servers may incorporate faster, higher-capacity hard drives, larger computer fans or water cooling to help remove heat, and uninterruptible power supplies that ensure the servers continue to function in the event of a power failure. These components offer higher performance and reliability at a correspondingly higher price. Hardware redundancy—installing more than one instance of modules such as power supplies and hard disks arranged so that if one fails another is automatically available—is widely used. ECC memory devices which detect and correct errors are used; non-ECC memory can cause data corruption.

Servers are often rack-mounted and situated in server rooms for convenience and to restrict physical access for security.

Many servers take a long time for the hardware to start up and load the operating system. Servers often do extensive preboot memory testing and verification and startup of remote management services. The hard drive controllers then start up banks of drives sequentially, rather than all at once, so as not to overload the power supply with startup surges, and afterwards they initiate RAID system prechecks for correct operation of redundancy. It is not uncommon for a machine to take several minutes to start up, but it may not need restarting for months or years.

Server (computing)

Usage in information technology.

In hardware

A server is a computer that has been set aside to run a specific server application. For example, when the software Apache HTTP Server is used as the web server for a company's website, the computer running Apache is also called the web server. Server applications can be divided among server computers over an extreme range, depending upon the workload.

Server is also used as a designation for computer models intended for use in running server applications under heavy workloads, also called operating units often unattended and for an extended period of time. While any workstation computer is capable of acting as a server, a server computer usually has special features intended to make it more suitable. These features can include a faster CPU, faster and more plentiful RAM, and larger hard drives. More obvious distinctions include redundancy in power supplies, network connections, and storage devices as well as the modular design of so-called Blade servers often used in server farms.

A server appliance refers to network-connected computer appliances or "appliance hardware" that provide specific, dedicated applications to a network. Use of the term appliance indicates the marriage of software and hardware in a single system that is not heavily customizable such as Google Search Appliance. Such appliances are expected to work out-of-the-box with little customization and sometimes remain the sole property of the company that produced them. The simplest appliances include switches, routers, gateways, and print servers.

In software

Server used as an adjective, as in server operating system, refers to the product's ability to handle multiple requests, and is said to be "server-grade". A server operating system is intended or better enabled to run server applications. The differences between the server and workstation versions of a product can vary from the removal of an arbitrary software limits due to licensing, as in the case of Windows 2000, or the addition of bundled applications as in Mac OS X Server.

Hosted service provider

A Hosted Service Provider (xSP) is a business that delivers a combination of traditional IT functions such as infrastructure, applications (Software as a Service), security, monitoring, storage, Web development, website hosting and email, over the Internet or other wide area networksapplication service provider (ASP) and an Internet service provider (ISP). (WAN). An xSP combines the abilities of an

This approach enables customers to consolidate and outsource much of their IT needs for a predictable recurring fee. xSPs that integrate Web publishing give customers a central repository to rapidly and efficiently distribute information and resources among employees, customers, partners and the general public.

Hosted Service Providers benefit from economies of scale and operate on a one-to-many business model, delivering the same software and services to many customers at once. Customers are charged on a subscription basis.

Internet hosting service

An Internet hosting service is a service that runs Internet servers, allowing organizations and individuals to serve content to the Internet. There are various levels of service and various kinds of services offered.

A common kind of hosting is web hosting. Most hosting providers offer a combined variety of services. Web hosting services also offer e-mail hosting service, for example. DNS hosting service is usually bundled with domain name registration.

Web hosting technology has been causing some controversy lately as Web.com claims that it holds patent rights to some common hosting technologies, including the use of a web-based control panel to manage the hosting service, with its 19 patents. Hostopia, a large wholesale host, recently purchased a license to use that technology from web.com for 10% of retail revenues. Web.com recently sued Go Daddy as well for similar patent infringement

Host (network)

In computer networking, a network host, Internet host or host is a computer connected to the Internet. A network host can host information as well as client and/or server software.

Every Internet host has a unique IP address, including a host address part. The host address is assigned either manually by the computer administrator, or automatically at start-up by means of the Dynamic Host Configuration Protocol (DHCP).

Every host is a network node (i.e. a network device), but every node is not a host. Network nodes such as modems and network switches are not assigned host addresses, and are not considered as hosts. Devices such as network printers and hardware routers are assigned IP host addresses, but since they are not general-purpose computers, they are sometimes not considered as hosts in the literature.

Origin of the concept

The term terminal host denotes a multi-user computer or software providing services to computer terminals, or a computer that provides services to smaller or less capable devices. ^[1]

The term host is used in a number of RFCs that define the Internet and its predecessor ARPANET. The background is that while ARPANET was developed, computers connected to the network were typically main frame computer systems that could be accessed from dumb terminals connected via serial ports. Since the terminals did not reside software, they were not considered as hosts. The terminals were not connected to the network, and were not assigned any IP host address. Part of the picture is also that a vision behind the Internet is that it should facilitate distributed computing, where information as well as client and server software easily can be moved and shared among computers.

Hosts file:

RFC 627 is an example of an early ARPANET standard, where the term hosts file is originally defined. This file is used to define locations of host computers. This is why the file was named hosts, literally a file with a list of hosts

Xhost:

In the X Window System, Xhost is a software that sends graphical data, sounds, etc, to a graphical terminal software at the user computer. Xhost is an example where the host is considered as client and the terminal as server according to the client-server model, since the host takes initiative to the process-to-process communication session, and the terminal is waiting for this initiative. See also Xbase-clients.