I. Starting point for dns resolution: user request
When a user enters a domain name in a browser (e. G. Www. Example. Com) and tries to access it, the process triggers the dns resolution. The user’s computer first checks if the domain name can be resolved directly through the local cache。
Ii. Local cache queries
As a first step, a user's computer or browser checks whether a parsing record of the domain name exists in its built-in dns cache. If the domain name has been previously visited and the cache has not expired, the computer will connect directly with the ip address in the cache, thus saving time for resolution。
Iii. Local dns server queries
Second, if no corresponding records are found in the local cache, the user's computer will send a query to the dns server in the local network. Local dns servers are usually provided by internet service providers (isps), which also maintain their own cache systems. Returns directly to the user computer if the domain name is recorded in the dns server cache。
Iv. Level-by-step queries
In the third step, if the local dns server cache is not recorded, the dns resolution process moves to the level-up query. Local dns servers send queries to root name servers. There are only a few root domain name servers worldwide, which manage and distribute top level domain name (tld) server address information。
Step four, the root domain server returns the top level domain name server address to the local dns server. The local dns server then sends a query to the top-level domain name server to obtain the address of the authoritative domain name server。
In the fifth step, after the top-level domain name server returns to the address of the authoritative domain name server, the local dns server then sends a query to the authoritative domain name server requesting that the ip address of the specific domain name be resolved。
V. Response to the authority diversity names
Step six, the authoritative domain name server returns the ip address of the domain name or other relevant records upon request. The local dns server caches this resolution so that in the future it can respond quickly to the same queries and return the results to the user computer。
User access to target servers
