An article to read DNS: the Internet's “address book” and DNS server knowledge

When traveling in the world of the Internet, DNS is like a silent “hero”, almost every time you surf the Internet can not do without it. However, many people don't know much about DNS and DNS servers. Today, let's take a deeper look at what they are.

First, what is DNS?

The websites we visit every day have an easy-to-remember domain name, such as “baidu.com”. But in the underlying world of the Internet, communication between computers relies on IP addresses, just like the reality of each house has a unique door number. However, a large website like Baidu may not have the same IP address in different regions in order to spread the traffic and reduce the pressure on the server. We can use the Ping command to check the IP address of a domain name in the region where it is located.

DNS, known as Domain Name System, is a distributed database that maps domain names and IP addresses to each other. Simply put, DNS is like the “address book” of the Internet world, which allows us to find the corresponding website without having to memorize the complicated IP addresses that may change at any time, just by typing in a memorable domain name.

For example, when we type “baidu.com” in the browser to visit Baidu, the computer does not know the IP address of the Baidu server directly. At this time, it will send a request to DNS, DNS query to “baidu.com” corresponding IP address, the information will be fed back to the computer, the computer will then find the Baidu server according to the IP address, to get the data we want.

In case of Baidu server failure, bandwidth upgrade, etc., which results in “baidu.com” needing to change its IP address, the DNS system will notify the DNS server of the new IP address. When the local DNS gets the new information, the next time the user visits this domain name, the local DNS will guide the user's network connection to the new IP address, to ensure that we can still access the website normally.

Knowledge of DNS server

DNS server plays a key role in the whole DNS system, according to the different functions and uses, it is mainly divided into the main server, auxiliary servers (also called slave servers), cache servers and forwarding servers.

(I) Main server

The master server is like a “big manager”, it hosts the control area file, which contains all the authoritative information of the domain. The master server obtains this information directly from the local file, and changes to the zone's DNS records can be made only on the master server. When the changes are complete, the primary server synchronizes the updated information to the secondary server.

(ii) Auxiliary server

The secondary server stores a read-only copy of the zone file, and it obtains information from the primary server through a communication method called zone transfer. Although DNS records for zones cannot be changed directly on the auxiliary server, under certain specific circumstances, the auxiliary server can pass a change request to the primary server to enable DNS record modification.

The presence of a secondary server is critical, and it serves two main purposes. On the one hand, when the primary server fails to shut down, the secondary server can timely top up to provide redundancy protection to ensure that the domain name resolution service is not interrupted and we can still access the relevant websites normally; on the other hand, the secondary server helps to distribute the load of user requests to the domain to avoid the primary server from being overloaded by too many requests and to prevent denial-of-service situations. In this process, auxiliary servers can use cyclic DNS technology, which is a load-balancing technology that allows each server in the domain to receive roughly equal traffic, improving the stability and efficiency of the entire system .

(C) Caching server

Cache server is like a “memory”, it will be the user's previous query of the domain name and IP address mapping relationship is temporarily stored. When there is a new request for the same query, the cache server can directly return the results from the cache, without the need to query other DNS servers, which greatly accelerates the speed of domain name resolution, reduces network delays, and improves the user's online experience.

(D) Forwarding server

The forwarding server is mainly responsible for receiving query requests from local DNS servers and forwarding these requests to other higher-level DNS servers for processing. It is like an “express relay station”, which can centralize the management and forwarding of query requests, improve query efficiency, and also help protect the security and privacy of the local network.