When asked what DNS is, many people know that it is related to domain names. Those who are more familiar with it know that DNS is a domain name resolution system, but in some people's impression, it is a domain name resolution service. Which one is correct? Since there is such a name, there is a certain reason and it does not come out of thin air. So what is the relationship between them? In fact, there are three DNSs:
One of DNS - Domain name structure, also known as DNS name structure. A domain name generally consists of English letters, Arabic numerals and a horizontal "-". It can be up to 67 characters (including suffixes), and there is no difference in the case of letters. Each level cannot exceed 22 letters. These symbols constitute the prefix, body and suffix of the domain name, which are combined to form a complete domain name.
Take a common domain name as an example. For example, the domain name www.baidu.com is composed of two parts. "baidu" is the main body of the domain name and also the host name, and the last "com" is the suffix of the domain name, which represents a com international domain name. The www. in front is the network name, and baidu.com is the domain name of www. Domain name language types can be diversified. In recent years, some countries have also developed and used domain names composed of their own national languages. Currently, domain names based on English are still the mainstream.
DNS 2 - Domain Name Server, that is, domain name service. The way to identify a computer on the Internet is to use IP, but a set of IP numbers is not easy to remember and has no meaning. At this time, "Domain Name" appeared That's called a domain name. The role of a domain name is only to facilitate memory. What can really be recognized by a computer is the IP. Therefore, when the user enters the Domain Name, the browser must first go to a host with corresponding information about the Domain Name and IP to query the IP of the computer. We call this host that was discovered the Domain Name Server.
For example, when we enter www.abc.com , the browser will send the name to the nearest DNS Server for identification. If found, it will return the IP of the host and then request information from it. However, If it is not found, a situation similar to DNS NOT FOUND will occur, so once the DNS Server crashes, the web page will not be able to be opened.
DNS No. 3 - Domain Name Systerm, literally translated as domain name system, is the basis for supporting the operation of DNS server. It consists of four parts: DNS domain name space, resource records, DNS server, and DNS client.
1. domain name space
The domain name space consists of root domain, top-level domain name, second-level domain name, sub-domain, etc.
2. resource record
Maps DNS domain names to specific types of resource information for use in name registration and resolution.
3． DNS server
Provides name lookup services for storing and answering resource records
4. DNS client
Used to query the DNS server and resolve the domain name to the resource record type specified in the query.
It can be seen that DNS has three different faces, or three twin brothers, each of which has different meanings. Domain name structure is for domain names, Domain Name Server is a dynamic resolution service process, and Domain Name Systerm is somewhat similar to Domain name structure, both are static, but it represents a wider range, including the entire domain name resolution system. . (Source: http://dns.qy.com.cn )