DNS (Domain Name System, Domain Name System), a distributed database on the Internet that maps domain names and IP addresses to each other, enables users to access the Internet more conveniently without having to remember IP strings that can be directly read by machines. The process of obtaining the IP address corresponding to the host name through the host name is called domain name resolution (or host name resolution).
The basic idea of CDN (Content Delivery Network) is to avoid bottlenecks and links on the Internet that may affect the speed and stability of data transmission, so as to make content transmission faster and more stable. By placing node servers everywhere in the network to form a layer of intelligent virtual network on the basis of the existing Internet, the CDN system can real-time based on network traffic and the connection and load status of each node, as well as the distance to the user and response time Such comprehensive information redirects the user's request to the service node closest to the user. Its purpose is to enable users to obtain the desired content nearby, solve the situation of Internet network congestion, and improve the response speed of users visiting websites.
If it is domain name resolution, DNS is essential, CDN is optional, CDN = smarter mirroring + caching + traffic diversion. Generally speaking, CDN is mainly used for different network acceleration.
1. DNS basic
Domain Name System, simply put, is to resolve a domain name to the corresponding IP address, it is fine, there are recursive query and iterative query. The port number it uses is 53.
2. How does the local domain name server know the IP of the root domain name server during resolution?
At present, there are 13 root domain name servers in the world, of which 1 is the main root, in the United States; 12 are auxiliary roots, of which 9 are in the United States, 2 are in Europe, and 1 is in Japan. There is a redundant relationship between these root domain name servers, mainly to prevent problems with each of them, and to allow other servers to be selected nearby. Each domain name has to go through the root name server to get the top-level index. Now, there are more than 200 mirror servers of root name servers around the world.
Since the root domain name servers are fixed, the local domain name server needs to know where the root server is, as long as the IP addresses of those root servers are recorded in the local configuration file instead of the domain name, and they can be used directly when needed.
3. The simple process of DNS resolution
is to request the DNS server step by step until the request reaches a certain IP address. Each time the DNS server returns him either a certain IP address, or the DNS server address of the subdomain to be queried next time. (The specific process is in the back)
4. A record and CNAME
A record: used to specify the correspondence between domain names and IP addresses.
Quote: A (Address) record is used to specify the IP address record corresponding to the host name (or domain name). Users can point the website server under the domain name to their own web server. You can also set up subdomains of your domain name. Generally speaking, the A record is the IP of the server, and the domain name binding A record is to tell the DNS, when you enter the domain name, it will guide you to the server
CNAME record corresponding to the A record set in the DNS: it is the correspondence between the host name and the CNAME.
Reference: CNAME (Canonical Name) records, usually referred to as aliases. Here, you can define a host alias, such as setting ftp.***.com to point to a host www.***.com, then you can use FTP.***.com to access www. ***.com now.
5. What is a CDN?
CDN is Content Delivery Network, CDN DNS is DNS first, the main function of this DNS is: when a telecom user requests service, it will return the IP of the telecom server; when a China Unicom user requests service, it will send the China Unicom server's IP IP returned. This saves time overhead.