DNS Series one: DNS query principle

Most of the network traffic is based on TCP/IP, while TCP/IP traffic is based on IP address, but in the real network access who is willing to use IP address, because the IP address we remember inconvenient. To solve this problem, DNS is available.

DNS: Domain Name System users access to the Internet through the input www.luwenju.com actually entered a computer name, the user's computer to the DNS server, the server will respond to the request after the user's computer an IP address, The user's computer accesses the Internet at the IP address returned through the DNS server. As shown in the following figure

In the figure above, the DNS client queries the DNS server for the IP of a particular computer, and because the DNS server is able to respond to queries in its own DNS database, it returns the www.luwenju.com=192.168.1.100 from its own resource records to the client.

The client gives the computer name to the DNS server, and the server starts querying. DNS server query has four kinds: 1, recursive query 2, iterative query 3, forwarders 4, private root

The following query methods in these 4 respectively

1, recursive query:

When a DNS client sends a DNS server to request resolution of a computer name, the DNS server first looks for its own database, and if the database has the corresponding domain name and IP mapping information, returns the IP address of the domain name to the client. If the server does not find the resource record in its own database, the query fails

The DNS client first initiates a query request to the DNS server, and then the DNS server starts checking the resource record and returns it to the client if the resource record is found. If it is not found, you can find the record through forwarders and root hints. If the DNS server does not find the record by any means, the query is declared unsuccessful.