Introduction to Data Communications
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Domain Name Look-up Procedure

When a domain name is used, the IP stack doesn't understand domain names. It says "what is this? Is not an IP address!". The only thing the IP stack understands is IP addresses. The look-up order is as follows:

  1. The IP stack checks the hosts file to see if there is a domain name match to IP address. If there is, the IP address is used.
  2. If there is no match, the IP stack will look for a NIS server with its host file shared. If this service is not installed, the IP stack will jump to the next step.
  3. If there is still no match, the IP stack will send out a request to the domain name server configured during the network configuration to see if it knows whose IP address belongs to the domain name.
  4. If the domain name server doesn't know, it may make an enquiry to the next level up domain name server to see if it knows whose IP address belongs to the domain name and so on.

On the Internet, there are 13 top level root domain name servers. The current addresses and domain names are found at ftp://internic.net/domain/named.cache (also called named.ca and named.root)

	Domain Name		IP Address	Description

	A.ROOT-SERVERS.NET	198.41.0.4	formerly NS.INTERNIC.NET

	B.ROOT-SERVERS.NET	128.9.0.107	formerly NS1.ISI.EDU

	C.ROOT-SERVERS.NET	192.33.4.12	formerly C.PSI.NET

	D.ROOT-SERVERS.NET	128.8.10.90	formerly TERP.UMD.EDU

	E.ROOT-SERVERS.NET	192.203.230.10	formerly NS.NASA.GOV

	F.ROOT-SERVERS.NET	192.5.5.241	formerly NS.ISC.ORG

	G.ROOT-SERVERS.NET	192.112.36.4	formerly NS.NIC.DDN.MIL

	H.ROOT-SERVERS.NET	128.63.2.53	formerly AOS.ARL.ARMY.MIL

	I.ROOT-SERVERS.NET	192.36.148.17	formerly NIC.NORDU.NET

	J.ROOT-SERVERS.NET	198.41.0.10	temporarily housed at NSI (InterNIC)

	K.ROOT-SERVERS.NET	193.0.14.129	housed in LINX, operated by RIPE NCC

	L.ROOT-SERVERS.NET	198.32.64.12	temporarily housed at ISI (IANA)

	M.ROOT-SERVERS.NET	202.12.27.33	housed in Japan, operated by WIDE

These are controlled by InterNIC which is the primary agency responsible for registering domain names. At the time of this writing, there are several new agencies that are taking over the domain registration process for different parts of the world.

Introduction to Data Communications
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