TCP/IP Animation , DNS
DNSWhen PC accesses any web service server, it needs to know the registered global IP address of the destination server. So as to get the address, it must tell DNS server the domain of the destination and ask it to convert it to IP address. The procedure is as follows.1. First it asks DNS server in the LAN. If the DNS server has the IP address information of the destination in its cache, the DNS server tells the address.2. If DNS server in the LAN doesn't know the address, it asks one of the 13 DNS root servers which are put in the world about IP address of the domain (like ogumo.co.jp) in the URI.3. Root server knows only the IP address of TLD DNS servers which manage TLD such as 'com', 'us' and 'jp'. Thus it returns IP address of the TLD server.4. After receiving the address, DNS server in the LAN asks the TLD server. If it knows the address, it returns the address. Otherwise it returns the address of SLD which manages such as 'ne', 'co' and 'or'.5. In this way the server which knows the IP address returns the address. After getting IP address of the domain, DNS server in the LAN asks DNS server in the destination LAN to convert the target (like http://www.ogumo.co.jp) to IP address.
(https://www.ogumo.co.jp)Converts the destination to global IP address.1.PC : Asks ISP DNS server about the IP address of the target.2.ISP : Asks DNS root server.3.Root : I know only ccTLD ' .jp ' server address.Ask it.4.ISP : Asks ccTLD ' .jp ' server.5.ccTLD(.jp) : I know only ccSTD ' .co.jp ' server address.Ask it.6.ISP : Asks ccSTD ' .co.jp ' server.7.ccSTD(.co.jp) : Converts the domain to global IP address. 'ogumo.co.jp → 220.127.116.11'8.ISP : Got IP address of the domain.9.ISP : Asks about IP address of the target server in the LAN.10.ogumo.co.jp : Tells the target server address. '18.104.22.168'11.ogumo.co.jp : Returns the IP address.12.ISP : Returns the IP address.13.PC : Got IP address of the target server.
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