1. Application layer: Domain Name System DNS (Domain Name System)
Source of notes:
Teacher at Lake University of Science and Technology: Overview of the Application Layer
Teacher at Lake University of Science and Technology: Domain Name System DNS
Disclaimer: The study notes are from a teacher at HuUST and are for study reference only.
DNS messages are encapsulated using the UDP protocol of the transport layer, and the transport layer port number is 53.
The role of domain name system DNS
Domain name (www.×××.com) -> DNS -> IP address -> ARP -> MAC address
The Internet cannot use only one DNS server. Because the Internet is huge, only one DNS server will be unable to work properly due to overload. Once the only DNS server is paralyzed, the entire Internet will be paralyzed. The Internet uses a hierarchical naming tree as the host name
. and use distributed DNS
Hierarchical tree structure of domain name structure
Top-level domain classification
Internet domain name space
Root domain name server (query website: DNS ICANN )
Four types of domain name servers
Root domain name server: does not directly resolve the domain name, but returns the IP address of the top-level domain name server to which the domain name belongs. Top-level domain name
server: manages all second-level domain names registered on the server.
Domain name server: is responsible for managing a certain zone. Domain name
local domain name server: proxy function, forwarding messages to the hierarchical structure of the top-level domain name server and authority domain name server mentioned above
Domain name resolution process
Recursive query
Iterative query
In order to improve the efficiency of DNS query and reduce the load on the root domain name server, the domain name server uses cache.
If there is a cache of the IP address to be checked in the local domain name server, there is no need to iterate the query.
If there is no IP address to be checked in the local domain name server To cache the address, you need to iteratively query the root domain name server, top-level domain name server, and authority domain name server.
