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What is DNS
DNS is the abbreviation of Domain Name System (Domain Name System). It is a computer and network service naming system organized into a domain hierarchy. It is used in TCP/IP networks. The service it provides is used to convert host names and domain names. Works for IP addresses.
addressing process
- On the local host
When we enter the url in the browser, we will first check whether the browser cache and the local hosts file have the mapping of this domain name. If so, we will call the ip address mapping and the resolution is completed. If there is no mapping of this domain name in hoots, it will search the cache of the local DNS resolver to see if there is a mapping relationship of this URL. If so, it will return directly to complete the domain name resolution. - On the local server
If there is no corresponding URL mapping relationship between hosts and the local fiDNS resolver cache, it will first find the preferred DNS server set by the TCP/ip parameter, that is, the local DNS server. When the local DNS server receives the query, if the domain name to be queried is included in the resources in the local configuration area, it will return the resolution, which is authoritative. If the domain name to be queried is not included in the resources in the local configuration area, but the server has cached the mapping relationship of the URL, the resolution result will be returned and the query will end. The resolution is not authoritative.
If the local DNS server fails and the forwarding mode (iteration) is not adopted between network servers, the local DNS will send requests to 13 root DNSs. After receiving the request, the root DNS server will determine who is authorized to manage the domain name and return An IP responsible for the top-level domain name server. After receiving the top-level server IP information, the local DNS server will continue to send requests to the top-level domain name server IP. If the server cannot be resolved, the thief will find the IP of the next-level DNS server responsible for this domain name For the local DNS server, always select loop until the query finds the mapping, then return the resolution result to the local DNS server, and then the local DNS server returns the resolution result. If the forwarding mode is adopted, the DNS server will forward the request to the upper-level DNS server, and send it up until the query result is obtained, and finally return the query result to the local DNS server, and then the local DNS server returns the result.
