Domain Name System - Revision history

Ngck: /* External Links */

2009-04-13T00:18:08Z

External Links

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	* [http://www.zytrax.com/books/dns/ DNS For Rocket Scientists: An Open Source Guide of DNS]		* [http://www.zytrax.com/books/dns/ DNS For Rocket Scientists: An Open Source Guide of DNS]
	* [http://www.bind9.net/ DNS & BIND]		* [http://www.bind9.net/ DNS & BIND]
-	--Jacky Ng ([[User:Ngck\|Ngck]]) 20:11, 12 April 2009 (EDT)	+	--Jacky Ng ([[User:Ngck\|Ngck]]) 20:18, 12 April 2009 (EDT)

Ngck: /* See Also */

2009-04-13T00:17:34Z

Ngck: /* External Links */

2009-04-13T00:14:56Z

External Links

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	== External Links ==		== External Links ==
-	* "[http://technet.microsoft.com/en-us/library/cc772774.aspx How DNS Works: Domain Name System(DNS)]".	+	* [http://technet.microsoft.com/en-us/library/cc772774.aspx How DNS Works: Domain Name System(DNS)]
-	* "[http://icann.org Internet Corporation for Assigned Names and Numbers (ICANN)]".	+	* [http://icann.org Internet Corporation for Assigned Names and Numbers (ICANN)]
-	--Jacky Ng ([[User:Ngck\|Ngck]]) 20:03, 12 April 2009 (EDT)	+	* [http://queue.acm.org/detail.cfm?id=1242499 DNS Complexity]
		+	* [http://www.zytrax.com/books/dns/ DNS For Rocket Scientists: An Open Source Guide of DNS]
		+	* [http://www.bind9.net/ DNS & BIND]
		+	--Jacky Ng ([[User:Ngck\|Ngck]]) 20:11, 12 April 2009 (EDT)

Ngck at 00:04, 13 April 2009

2009-04-13T00:04:09Z

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	* "[http://technet.microsoft.com/en-us/library/cc772774.aspx How DNS Works: Domain Name System(DNS)]".		* "[http://technet.microsoft.com/en-us/library/cc772774.aspx How DNS Works: Domain Name System(DNS)]".
	* "[http://icann.org Internet Corporation for Assigned Names and Numbers (ICANN)]".		* "[http://icann.org Internet Corporation for Assigned Names and Numbers (ICANN)]".
-	--Jacky Ng ([[User:Ngck\|Ngck]]) 00:27, 8 April 2009 (EDT)	+	--Jacky Ng ([[User:Ngck\|Ngck]]) 20:03, 12 April 2009 (EDT)

Ngck at 00:03, 13 April 2009

2009-04-13T00:03:19Z

Ngck: /* Domain Name Resolution */

2009-04-11T22:40:48Z

Domain Name Resolution

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	=== Domain Name Resolution ===		=== Domain Name Resolution ===
-	In theory, the domain name resolution operates in a top-down approach, starting from the root name server and traces its way down to the servers at the leaves of the hierarchical tree. There are two ways of using DNS:	+	In theory, the domain name resolution operates in a top-down approach, starting from the root name server and traces its way down to the servers at the leaves of the hierarchical tree. There are two ways of using DNS:<sup>[1]</sup>
	# The client sends a query to each of the name server one at a time		# The client sends a query to each of the name server one at a time
	# The client sends a query to one of the name server and makes the name server carry out the whole mapping.		# The client sends a query to one of the name server and makes the name server carry out the whole mapping.
	In either of the case, the client is required to send a query containing the domain name that is needed to be mapped to the name server.		In either of the case, the client is required to send a query containing the domain name that is needed to be mapped to the name server.

-	When the name server receives the query sent by the client, the server checks to see if the domain name is under its subdomain. If the domain name is under its subdomain, the server will map the name to the address and append the answer onto the client’s query and send back the answer to the client. However, if the domain name is not under its subdomain, the server checks the type of interaction the client specified. There are two types of DNS query that can the client can send:	+	When the name server receives the query sent by the client, the server checks to see if the domain name is under its subdomain. If the domain name is under its subdomain, the server will map the name to the address and append the answer onto the client’s query and send back the answer to the client. However, if the domain name is not under its subdomain, the server checks the type of interaction the client specified. There are two types of DNS query that can the client can send:<sup>[1]</sup>
	# ''Non-recursive Resolution'' (''Iterative Resolution'')		# ''Non-recursive Resolution'' (''Iterative Resolution'')
	# ''Recursive Resolution'' (''Complete Resolution'')		# ''Recursive Resolution'' (''Complete Resolution'')
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	In order for the client to start a query, the client needs to know which name server to start the search from. Additionally, the client needs to know at least one of the addresses of the name server. Moreover, DNS requires that each server knows at least one of the address of its root server or parent.		In order for the client to start a query, the client needs to know which name server to start the search from. Additionally, the client needs to know at least one of the addresses of the name server. Moreover, DNS requires that each server knows at least one of the address of its root server or parent.
-	Domain name servers communicate with each other using both TCP and UDP. In addition, the name servers listen on TCP and UDP ports 53. As a result, the client knows how to communicate with the name server once it knows the IP address of the server.	+	Domain name servers communicate with each other using both TCP and UDP.<sup>[6]</sup> In addition, the name servers listen on TCP and UDP ports 53.<sup>[6]</sup> As a result, the client knows how to communicate with the name server once it knows the IP address of the server.

	=== Caching ===		=== Caching ===

Ngck: /* Top-Level Domains */

2009-04-11T22:39:20Z

Top-Level Domains

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	=== Top-Level Domains ===		=== Top-Level Domains ===
-	[[Image:Internet Domain Name.jpg\|thumb\|A small part of the Internet domain name hierarchy.<sup>[1]</sup>]]The Internet's DNS currently uses a set of official top-level domain names (TLDs). These set of TLDs are maintained by the Internet Corporation for Assigned Names and Numbers (ICANA). Currently, ICANA disguishes the following groups of TLDs:	+	[[Image:Internet Domain Name.jpg\|thumb\|A small part of the Internet domain name hierarchy.<sup>[1]</sup>]]The Internet's DNS currently uses a set of official top-level domain names (TLDs). These set of TLDs are maintained by the Internet Corporation for Assigned Names and Numbers (ICANA). Currently, ICANA disguishes the following groups of TLDs:<sup>[5]</sup>

	* Infrastructure top-level domain		* Infrastructure top-level domain

Ngck: /* Domain Registration */

2009-04-11T22:36:49Z

Domain Registration

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	== Domain Registration ==		== Domain Registration ==
-	The right to use a domain name is authorized by ''domain name registrars''. In addition, domain name registrars are accredited by ICANN. Each top-level domain (TLD) is maintained by InterNIC, which is also operated by ICANN. InterNIC receives domain name registration information provided by the domain name registrars and publishes the information. There is an annual fee for the service of authorizing domain name to a user. The authorized users are known as “registrants” or as “domain holders”.	+	The right to use a domain name is authorized by ''domain name registrars''.<sup>[7]</sup> In addition, domain name registrars are accredited by ICANN.<sup>[7]</sup> Each top-level domain (TLD) is maintained by InterNIC, which is also operated by ICANN. InterNIC receives domain name registration information provided by the domain name registrars and publishes the information.<sup>[7]</sup> There is an annual fee for the service of authorizing domain name to a user. The authorized users are known as “registrants” or as “domain holders”.

	== References ==		== References ==

Ngck: /* References */

2009-04-11T22:36:09Z

References

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	# "[http://www.lagunainternet.com/techsupport/history_of_dns.htm History of the Domain Name System]". Retrieved on 2009-04-07.		# "[http://www.lagunainternet.com/techsupport/history_of_dns.htm History of the Domain Name System]". Retrieved on 2009-04-07.
	# "[http://www.mapsofworld.com/referrals/internet/internet-history/history-of-domain-name-system.html History of Domain Name System]". Retrieved on 2009-04-07.		# "[http://www.mapsofworld.com/referrals/internet/internet-history/history-of-domain-name-system.html History of Domain Name System]". Retrieved on 2009-04-07.
-	# "[http://www.icann.org/en/registries/about.htm ICANN \| About gTLDs]". Retrieved on 2009-04-09	+	# "[http://www.icann.org/en/registries/about.htm ICANN \| About gTLDs]". Retrieved on 2009-04-09.
	# William, F. M. (2009). Domain Name System (DNS). In ''Lecture 09: Common Network Services''.		# William, F. M. (2009). Domain Name System (DNS). In ''Lecture 09: Common Network Services''.
		+	# "[http://www.icann.org/en/faq/ ICANN \| FAQs]". Retrieved on 2009-04-09.

	== See Also ==		== See Also ==

Ngck: /* Domain Registration */

2009-04-11T20:52:40Z

Domain Registration

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	== Domain Registration ==		== Domain Registration ==
-	The right to use a domain name is authorized by ''domain name registrars''. In addition, domain name registrars are accredited by ICANN. Each top-level domain (TLD) is maintained by ~~a sponsoring organization called the ''TLD Registry''~~. ~~The TLD Registry~~ receives domain name registration information provided by the domain name registrars and publishes the information. There is an annual fee for the service of authorizing domain name to a user. The authorized users are known as “registrants” or as “domain holders”.	+	The right to use a domain name is authorized by ''domain name registrars''. In addition, domain name registrars are accredited by ICANN. Each top-level domain (TLD) is maintained by InterNIC, which is also operated by ICANN. InterNIC receives domain name registration information provided by the domain name registrars and publishes the information. There is an annual fee for the service of authorizing domain name to a user. The authorized users are known as “registrants” or as “domain holders”.

	== References ==		== References ==

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	== See Also ==		== See Also ==
	* [http://en.wikipedia.org/wiki/Dynamic_DNS Dynamic DNS]		* [http://en.wikipedia.org/wiki/Dynamic_DNS Dynamic DNS]
		+	* [http://en.wikipedia.org/wiki/DNSSEC DNS Security Extensions (DNSSEC)]
		+	* [http://en.wikipedia.org/wiki/DNS_management_software DNS Management Software]
		+	* [http://en.wikipedia.org/wiki/Comparison_of_DNS_server_software Comparison Of DNS Server Software]
	* [http://www.cas.mcmaster.ca/wiki/index.php/DHCP DHCP]		* [http://www.cas.mcmaster.ca/wiki/index.php/DHCP DHCP]

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	== History of DNS ==		== History of DNS ==
-	In the late 1960s, the U.S. Department of Defense Advanced Research Projects Agency (ARPA, later known as DARPA) funded and began working toward an internet technology called the ARPANET.<sup>[1]</sup> Each computer on the network was given an address for interconnecting with other computers on the network. ~~In addition, this~~ information was stored on a central site, called the Network Information Center (NIC), in a single file named HOSTS.TXT.<sup>[3,4]</sup> ~~Moreover, the~~ HOSTS.TXT file ~~contains~~ information regarding the name-to-address mapping of all computers connected to the ARPANET.<sup>[3]</sup> Each computer on the network needed to retrieve this file in order to communication with other computers on the network.<sup>[3]</sup> With only a small ~~amount~~ of computers interconnected at the ~~start~~, HOSTS.TXT worked well. However, there are limitations with this scheme. If there is a change in the address in one of the computers on the network, every computer that ~~want~~ to ~~communication~~ with that machine ~~would need~~ to update its host file. Also, as the network traffic ~~increases~~, there is a need to overcome problems such as overlapping names. ~~As a result,~~ DNS was invented to solve these limitations.	+	In the late 1960s, the U.S. Department of Defense Advanced Research Projects Agency (ARPA, later known as DARPA) funded and began working toward an internet technology called the ARPANET.<sup>[1]</sup> Each computer on the network was given an address for interconnecting with other computers on the network. This information was stored on a central site, called the Network Information Center (NIC), in a single file named HOSTS.TXT.<sup>[3,4]</sup> The HOSTS.TXT file contained information regarding the name-to-address mapping of all computers connected to the ARPANET.<sup>[3]</sup> Each computer on the network needed to retrieve this file in order to communication with other computers on the network.<sup>[3]</sup> With only a small number of computers interconnected in the beginning, HOSTS.TXT worked well. However, there are limitations with this scheme. First, if there was a change in the address of one of the computers on the network, every computer that wanted to communicate with that machine was forced to update its host file. Also, as the network traffic increased, there was a need to overcome problems such as overlapping names. DNS was invented to solve these limitations.

	The Domain Name System was invented by Jon Postel, Paul Mockapetris and Craig Partrige in 1983.<sup>[4]</sup> In addition, they published the original specification, RFC 882, for the DNS.<sup>[4]</sup> Over the years, several more RFCs have been published to update the DNS specification, making the RFC 882 obsolete.		The Domain Name System was invented by Jon Postel, Paul Mockapetris and Craig Partrige in 1983.<sup>[4]</sup> In addition, they published the original specification, RFC 882, for the DNS.<sup>[4]</sup> Over the years, several more RFCs have been published to update the DNS specification, making the RFC 882 obsolete.
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	[[Image:Domain Namespace.jpg\|thumb\|Delegation of authority for names in the Domain Name System.]]		[[Image:Domain Namespace.jpg\|thumb\|Delegation of authority for names in the Domain Name System.]]
	The DNS uses a hierarchical naming scheme. A hierarchical naming scheme operates similar to the management structure of a business organization. At the top level, the namespace is divided and each division is delegated with authority.<sup>[1]</sup> In addition, if there is a change in a division, the top level would not be affected.<sup>[1]</sup>		The DNS uses a hierarchical naming scheme. A hierarchical naming scheme operates similar to the management structure of a business organization. At the top level, the namespace is divided and each division is delegated with authority.<sup>[1]</sup> In addition, if there is a change in a division, the top level would not be affected.<sup>[1]</sup>
-	The syntax of the assigned names often reflects the hierarchical ~~authority delegated~~.<sup>[1]</sup> Using the following namespace as an example:	+
		+	The syntax of the assigned names often reflects the hierarchical structure.<sup>[1]</sup> Using the following namespace as an example:
	<center>''local.site''</center>		<center>''local.site''</center>
-	''site'' is the name of the site authorized by the central authority; ''local'' is the part that is controlled by the site. The period (“.”) is a delimiter to separate the names. ~~Such~~ hierarchical naming scheme is known as domain ~~names~~. Domain name is a name consisting of a sequence of labels separated by periods (dots).<sup>[1]</sup> Each suffix of a domain name is also a domain name. In addition, a domain name denotes a set of one or more hosts. In the case of a domain name denoting a single host (known as a ''host name''), the domain name looks no different from a domain name denoting a set of hosts.	+	''site'' is the name of the site authorized by the central authority; ''local'' is the part that is controlled by the site. The period (“.”) is a delimiter to separate the names. This type of hierarchical naming scheme is known as domain name. Domain name is a name consisting of a sequence of labels separated by periods (dots).<sup>[1]</sup> Each suffix of a domain name is also a domain name. In addition, a domain name denotes a set of one or more hosts. In the case of a domain name denoting a single host (known as a ''host name''), the domain name looks no different from a domain name denoting a set of hosts.

	=== Subset Authority ===		=== Subset Authority ===
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	=== Top-Level Domains ===		=== Top-Level Domains ===
-	[[Image:Internet Domain Name.jpg\|thumb\|A small part of the Internet domain name hierarchy.<sup>[1]</sup>]]The Internet's DNS currently uses a set of official top-level domain names (TLDs). These set of TLDs are maintained by the Internet Corporation for Assigned Names and Numbers (~~ICANA~~). Currently, ~~ICANA disguishes~~ the following groups of TLDs:<sup>[5]</sup>	+	[[Image:Internet Domain Name.jpg\|thumb\|A small part of the Internet domain name hierarchy.<sup>[1]</sup>]]The Internet's DNS currently uses a set of official top-level domain names (TLDs). These set of TLDs are maintained by the Internet Corporation for Assigned Names and Numbers (ICANN). Currently, ICANN distinguishes the following groups of TLDs:<sup>[5]</sup>

	* Infrastructure top-level domain		* Infrastructure top-level domain
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	[[image:Conceptual_Arrangement_of_Server.jpg\|thumb\|The conceptual arrangement of domain name servers in a tree that corresponds to the naming hierarchy.<sup>[1]</sup>]]		[[image:Conceptual_Arrangement_of_Server.jpg\|thumb\|The conceptual arrangement of domain name servers in a tree that corresponds to the naming hierarchy.<sup>[1]</sup>]]
	[[image:Realistic_Arrangement_of_Server.jpg\|thumb\|The realistic arrangement of domain name servers in a tree that corresponds to the naming hierarchy.<sup>[1]</sup>]]		[[image:Realistic_Arrangement_of_Server.jpg\|thumb\|The realistic arrangement of domain name servers in a tree that corresponds to the naming hierarchy.<sup>[1]</sup>]]
-	The DNS uses the ''client-server model''. On the server side, the mechanism that DNS uses to map domain names to addresses is a set of independent, cooperative systems called ''name servers''.<sup>[1]</sup> A name server is a server program that maps domain names to IP addresses. On the client side, there is a client software, called ''name resolver'', which uses one or more name servers when mapping a name to IP address.<sup>[1]</sup> It is used to initiate the queries for the mapping.	+	The DNS uses the ''client-server model''. On the server side, the mechanism that DNS uses to map domain names to addresses is a set of independent, cooperative systems called ''name servers''.<sup>[1]</sup> A name server is a server program that maps domain names to IP addresses. On the client side, there is a client software, called ''name resolver'', which uses one or more name servers when mapping a name to IP address.<sup>[1]</sup> It is used to initiate the queries for the mapping. In a conceptual arrangement of domain name servers, each server knows the addresses of all lower-level servers for all subdomains within the domain it handles.<sup>[1]</sup> However, in reality, servers are combined together since a single server can be used to store all of the information.<sup>[1]</sup>
-	In a conceptual arrangement of domain name servers, each server knows the addresses of all lower-level servers for all subdomains within the domain it handles.<sup>[1]</sup> However, in reality, servers are combined together since a single server can be used to store all of the information.<sup>[1]</sup>	+

	=== Domain Name Resolution ===		=== Domain Name Resolution ===
-	In theory, the domain name resolution operates in a top-down approach~~, starting~~ from the root name server and traces its way down to the servers at the leaves of the hierarchical tree. There are two ways of using DNS:<sup>[1]</sup>	+	In theory, the domain name resolution operates in a top-down approach. It starts from the root name server and traces its way down to the servers at the leaves of the hierarchical tree. There are two ways of using DNS:<sup>[1]</sup>
	# The client sends a query to each of the name server one at a time		# The client sends a query to each of the name server one at a time
	# The client sends a query to one of the name server and makes the name server carry out the whole mapping.		# The client sends a query to one of the name server and makes the name server carry out the whole mapping.
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	If the client specified for non-recursive resolution, the server will generate a reply and suggest the next name server that the client should look to resolve the name, or give an error. On the other hand, if the client specified for recursive resolution, the server will contact another name server that can map the name and send the answer back to the client, or give an error.		If the client specified for non-recursive resolution, the server will generate a reply and suggest the next name server that the client should look to resolve the name, or give an error. On the other hand, if the client specified for recursive resolution, the server will contact another name server that can map the name and send the answer back to the client, or give an error.

-	In order for the client to start a query, the client needs to know which name server to start the search from. Additionally, the client needs to know at least one of the addresses of the name server. Moreover, DNS requires that each server ~~knows~~ at least one of the address of its root server or parent.	+	In order for the client to start a query, the client needs to know which name server to start the search from. Additionally, the client needs to know at least one of the addresses of the name server. Moreover, DNS requires that each server know at least one of the address of its root server or parent.
	Domain name servers communicate with each other using both TCP and UDP.<sup>[6]</sup> In addition, the name servers listen on TCP and UDP ports 53.<sup>[6]</sup> As a result, the client knows how to communicate with the name server once it knows the IP address of the server.		Domain name servers communicate with each other using both TCP and UDP.<sup>[6]</sup> In addition, the name servers listen on TCP and UDP ports 53.<sup>[6]</sup> As a result, the client knows how to communicate with the name server once it knows the IP address of the server.

	=== Caching ===		=== Caching ===
-	Due to large amount of queries send by the resolvers to the root server, there is an extremely high cost ~~of lookup for~~ names. In addition, name lookup can present a heavy load on the Internet. As a result, there is a need to reduce the load on the DNS servers and reduce the number of lookups for names.	+	Due to large amount of queries send by the resolvers to the root server, there is an extremely high cost associated with looking up names. In addition, name lookup can present a heavy load on the Internet. As a result, there is a need to reduce the load on the DNS servers and reduce the number of lookups for names.

	The Internet name servers use ''caching'' to improve the search costs.<sup>[1]</sup> Each server maintains a cache of recently looked up names as well as a record of where the names are from. When the client sends a request to the server to map a name, the server will first check to see if the domain name is under its subdomain. If not, the server checks its cache to see if the domain name has recently been resolved. The server will send its cached information (the address and which name server it’s from) back to the client and the information is marked as ''nonauthoritative'' binding.<sup>[1]</sup> As a result, the client receives the information quickly. However, the information could be outdated and be incorrect. To keep the cache correct, servers keep track of the time of the entries and discard entries that exceed a certain time limit. If the server is asked for the information that it removed, the server will have to go through the domain name resolution process again. The servers do not apply a fixed time to remove the outdated information; instead, they allow the authority to enter in a Time To Live (TTL) value to specify how long it guarantees the binding to be valid.<sup>[1]</sup>		The Internet name servers use ''caching'' to improve the search costs.<sup>[1]</sup> Each server maintains a cache of recently looked up names as well as a record of where the names are from. When the client sends a request to the server to map a name, the server will first check to see if the domain name is under its subdomain. If not, the server checks its cache to see if the domain name has recently been resolved. The server will send its cached information (the address and which name server it’s from) back to the client and the information is marked as ''nonauthoritative'' binding.<sup>[1]</sup> As a result, the client receives the information quickly. However, the information could be outdated and be incorrect. To keep the cache correct, servers keep track of the time of the entries and discard entries that exceed a certain time limit. If the server is asked for the information that it removed, the server will have to go through the domain name resolution process again. The servers do not apply a fixed time to remove the outdated information; instead, they allow the authority to enter in a Time To Live (TTL) value to specify how long it guarantees the binding to be valid.<sup>[1]</sup>