Domain Name System (DNS)
If you use the Internet to do your work like sending e-mail or browsing the Web, then you use Domain Name Systems (DNS) without even realizing it. The DNS translates human-friendly computer hostnames into IP addresses. For example, ipcnetworking.com translates to 216.239.34.21.
Human readable names like blog.ipcnetworking.com are easier to remember than IP addresses such as 216.239.34.21. 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 DNS system is a database. It forms one of the largest and most active distributed databases on the planet. DNS 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.
A name server would start its search for an IP address by contacting one of the root name servers. The root servers know the IP address for all of the name servers that handle the top-level domains. Every DNS server will have to maintain a root cache file so that they know how to contact the root name server to retrieve information. A sample root cache file is listed below:
In general, the DNS 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 DNS is an essential component of the functionality of the Internet.A domain name usually consists of two or more parts (technically labels), which are conventionally written separated by dots, such as blog.ipcnetworking.com.The rightmost label conveys the top-level domain (for example, the address blog.chengsoongiap.com has the top-level domain com).Each label to the left specifies a subdivision, or subdomain of the domain above it. For example: ipcnetworking.com is a subdomain of the com domain, and blog.ipcnetworking.com is a subdomain of the domain ipcnetworking.com. In theory, this subdivision can go down 127 levels.
Human readable names like blog.ipcnetworking.com are easier to remember than IP addresses such as 216.239.34.21. 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 DNS system is a database. It forms one of the largest and most active distributed databases on the planet. DNS 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.
A name server would start its search for an IP address by contacting one of the root name servers. The root servers know the IP address for all of the name servers that handle the top-level domains. Every DNS server will have to maintain a root cache file so that they know how to contact the root name server to retrieve information. A sample root cache file is listed below:
; This file holds the information on root name servers needed to ; initialize cache of Internet domain name servers ; (e.g. reference this file in the "cache ." ; configuration file of BIND domain name servers). ; ; This file is made available by InterNIC ; under anonymous FTP as ; file /domain/named.cache ; on server FTP.INTERNIC.NET ; -OR- RS.INTERNIC.NET ; ; last update: Jun 8, 2011 ; related version of root zone: 2011060800 ; ; formerly NS.INTERNIC.NET ; . 3600000 IN NS A.ROOT-SERVERS.NET. A.ROOT-SERVERS.NET. 3600000 A 198.41.0.4 A.ROOT-SERVERS.NET. 3600000 AAAA 2001:503:BA3E::2:30 ; ; FORMERLY NS1.ISI.EDU ; . 3600000 NS B.ROOT-SERVERS.NET. B.ROOT-SERVERS.NET. 3600000 A 192.228.79.201 ; ; FORMERLY C.PSI.NET ; . 3600000 NS C.ROOT-SERVERS.NET. C.ROOT-SERVERS.NET. 3600000 A 192.33.4.12 ; ; FORMERLY TERP.UMD.EDU ; . 3600000 NS D.ROOT-SERVERS.NET. D.ROOT-SERVERS.NET. 3600000 A 128.8.10.90 D.ROOT-SERVERS.NET. 3600000 AAAA 2001:500:2D::D ; ; FORMERLY NS.NASA.GOV ; . 3600000 NS E.ROOT-SERVERS.NET. E.ROOT-SERVERS.NET. 3600000 A 192.203.230.10 ; ; FORMERLY NS.ISC.ORG ; . 3600000 NS F.ROOT-SERVERS.NET. F.ROOT-SERVERS.NET. 3600000 A 192.5.5.241 F.ROOT-SERVERS.NET. 3600000 AAAA 2001:500:2F::F ; ; FORMERLY NS.NIC.DDN.MIL ; . 3600000 NS G.ROOT-SERVERS.NET. G.ROOT-SERVERS.NET. 3600000 A 192.112.36.4 ; ; FORMERLY AOS.ARL.ARMY.MIL ; . 3600000 NS H.ROOT-SERVERS.NET. H.ROOT-SERVERS.NET. 3600000 A 128.63.2.53 H.ROOT-SERVERS.NET. 3600000 AAAA 2001:500:1::803F:235 ; ; FORMERLY NIC.NORDU.NET ; . 3600000 NS I.ROOT-SERVERS.NET. I.ROOT-SERVERS.NET. 3600000 A 192.36.148.17 I.ROOT-SERVERS.NET. 3600000 AAAA 2001:7FE::53 ; ; OPERATED BY VERISIGN, INC. ; . 3600000 NS J.ROOT-SERVERS.NET. J.ROOT-SERVERS.NET. 3600000 A 192.58.128.30 J.ROOT-SERVERS.NET. 3600000 AAAA 2001:503:C27::2:30 ; ; OPERATED BY RIPE NCC ; . 3600000 NS K.ROOT-SERVERS.NET. K.ROOT-SERVERS.NET. 3600000 A 193.0.14.129 K.ROOT-SERVERS.NET. 3600000 AAAA 2001:7FD::1 ; ; OPERATED BY ICANN ; . 3600000 NS L.ROOT-SERVERS.NET. L.ROOT-SERVERS.NET. 3600000 A 199.7.83.42 L.ROOT-SERVERS.NET. 3600000 AAAA 2001:500:3::42 ; ; OPERATED BY WIDE ; . 3600000 NS M.ROOT-SERVERS.NET. M.ROOT-SERVERS.NET. 3600000 A 202.12.27.33 M.ROOT-SERVERS.NET. 3600000 AAAA 2001:DC3::35 ; End of File
In general, the DNS 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 DNS is an essential component of the functionality of the Internet.A domain name usually consists of two or more parts (technically labels), which are conventionally written separated by dots, such as blog.ipcnetworking.com.The rightmost label conveys the top-level domain (for example, the address blog.chengsoongiap.com has the top-level domain com).Each label to the left specifies a subdivision, or subdomain of the domain above it. For example: ipcnetworking.com is a subdomain of the com domain, and blog.ipcnetworking.com is a subdomain of the domain ipcnetworking.com. In theory, this subdivision can go down 127 levels.
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