TCP/IP Animation , LAN, DHCP, NAT
LAN, DHCP, NATSo as to access website from PC or mobile device, the device needs to have a global IP address.The address is assigned by the router in the LAN which has NAT function when PC accesses website.The procedure is as follows.1.PC requests private IP address to DHCP server or router in the LAN.2.DHCP server assigns private IP address to it for a certain period.3.When the PC accesses web site, the private IP address is converted to a global IP address.4.After the web data is returned, it is sent to the PC according to IP address converted from global to private.Please operate this scene with turning on the PC and pushing 'Internet' button.*Static NATWeb server in this LAN is published. One private IP address and one global IP address are set pair and always fixed for this server.The gateway router manages this and converts these address when accessed from outside.It is called 'Static NAT'.
DHCP,NAPT1.PC1 : Searches DHCP server with ARP packet 'DHCP_DISCOVER' by broadcast.2.DHCP : Tells that DHCP server exists, with ARP packet 'DHCP_OFFER' by broadcast.3.PC1 : Requests IP address with ARP packet 'DHCP_REQUEST' by broadcast.4.DHCP : Assigns private IP address for a period, with ARP packet 'DHCP_ACK'.5.PC1 : Got private IP address.6.PC1 : Searches rooter or server as a relay node to access the destination server.7.Router : Returns its own MAC address by unicast.8.PC1 : Got the MAC address of the next node.9.PC1 : Accesses the website 'https://www.ogumo.co.jp'.10.Router : Changes the private IP address to global IP address.11.Router : Uses the common global IP address. And saves local address and port.12.Ogumo server : Got the request.13.Ogumo server : Sends the website contents.14.Router : Changes the IP address from global to private.15.Router : Sends the data to the local PC.16.PC1 : Got the website data.
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