What is Domain Name System
Source: Shangpin China |
Type: website encyclopedia |
Date: August 26, 2012
In the Internet, because of the uniform IP address Website production The applications of any two hosts on the can easily communicate using the IP address. But the IP address is a binary number with a length of 32 bits. Even if it is represented by four decimal numbers, it is very difficult for ordinary users to remember the IP address of such abstract numbers. In order to provide an intuitive host identifier (host name) to ordinary users, TCP 8P has specially designed a character based host naming mechanism, that is, to give each host a name composed of strings. This host name is a more advanced address form than IP addresses, which is the domain name system discussed in this section.
On the one hand, the Internet domain name system can give each host a name that is easy to remember, and on the other hand, it can also establish the mapping relationship between the host name and IP address. The domain name system can also complete the work of consulting various information of the host. Almost all application layer software needs to use the domain name system, for example, the Remote Terminal Protocol (Telnet), File Transfer Protocol (FTP), and Simple Mail Transfer Protocol (SMTP).
1. Naming mechanism and management of hierarchical domain name system
The simplest way to name a host on the network is that the name of each host is composed of a string. The address resolution is solved through the host name and IP address mapping table in the Network Information Center (NIC), and then the NIC is responsible for the allocation, confirmation and recycling of host names. This is called the "hierarchical naming mechanism", It looks simple on the surface. However, in fact, it cannot be applied to large-scale networks such as the Internet. The fundamental reason is that this naming mechanism has no structure.
With the increasing number of hosts on the Internet, the possibility of host name duplication is increasing, the burden of the network information center is increasing, and the maintenance of the address mapping table will become more and more difficult. Therefore, the Internet adopts a hierarchical naming mechanism. Generally, three aspects must be considered when naming hosts on the Internet: ① the host name is globally unique, that is, it can be used universally on the entire Internet; ② It shall be easy to manage; ③ To facilitate mapping. Since user level names cannot be accepted by protocols that use IP addresses, and IP addresses are not easily understood by ordinary users, there is a need for mapping between the two. The efficiency of mapping is a key issue. The specific solutions to the above three problems constitute a specific naming mechanism - hierarchical naming mechanism. The so-called "hierarchical" refers to the addition of a hierarchical structure to the name, so that it corresponds to the hierarchy of the Hierarchical Name Space management mechanism. The namespace is divided into several parts and authorized to be managed by the corresponding organization. The management authority has the right to further divide the namespaces under its jurisdiction and authorize the corresponding authority to manage them. If this continues, the organization and management of namespaces will form a tree like hierarchical structure. The management organizations of each layer and the final host are represented as nodes in the tree structure and are represented with corresponding identifiers.
DNS is a distributed host information database, which manages the host name and IP address of the entire Internet.
The domain name system is managed hierarchically. Therefore, the distributed host information database is also hierarchical, similar to the structure of the file system in the computer. The whole database is an inverted tree structure, as shown in Figure 5-10. The top is the root. The root name is an empty tag "", but it is written as "." in the text format. Each node in the tree represents a part of the entire database, that is, the domain of the domain name system. The domain can be further divided into sub domains. Each domain has a domain name that defines its location in the database. In the domain name system, the full name of a domain name is a string of all tags from the sub domain name up to the root, separated by ".".
In the hierarchical naming mechanism management, the division of the highest level namespace is based on the "Site Name". As a part of the entire Internet, a node is composed of several networks, which are closely linked in geographical location or organizational relationship. Therefore, an Internet treats 4111 as a two point. For example, commercial organizations (COM) , educational institution (EDU) and a country code<Country Code>. There are several "Administrative Croup" in each node. Therefore, the division of the second level namespace is based on the "Group Name", and the "local name" of each host is below the group name. Generally, a complete and universal hierarchical hostname consists of three parts.
Sometimes the local name of the host may be a specific organization or network, which is called "sub domain". The subdomain can be preceded by a host name, so the hierarchical host name can be expressed as: host name, local name, group name, network point name. For example, if the name of a host computer is www.nlc.gov.en, it means the name of a host computer of the National Library of China.
2. Internet Domain Name System
The hierarchical name management mechanism implemented by the Internet is called Domain Name System (DNS). In order to ensure the universality of the domain name system, the Internet has formulated a set of formal general standard codes as the first level domain names.
In the first level domain name code, the first eight domain names correspond to the organization mode, and the next one corresponds to the geographical mode. The organizational model is the organizational domain name generated by dividing the organizational management hierarchy, which is composed of three letters, such as EDU, COM, etc. In 1997, seven first level domain names were added, namely, FIM, STORE, WEB, ARTS, REC, INFO, and NOM. The geographical model is the geographical domain name generated by the geographical division of countries and regions. This type of domain name is the name of countries and regions in the world, and is composed of two letters. As shown in Table 5-2, it is some region codes.
The highest level domain name of the Internet in China is "CN". There are 40 secondary domain names, which are divided into 6 "category domain names", including AC, CObI, EDU, GOV, NET and OHG. 34 "administrative domain names", for example, Il BJ (Beijing), SH (Shanghai), TJ (Tianjin) and zi (Zhejiang), etc.
3. Working principle of domain name system
Identifying a host's domain name in a familiar natural language is easier to remember than using a numeric IP address. However, the host domain name cannot be directly used in TCP 8-P routing. When users use the host domain name for communication, they must first map it to an IP address. Because of the Internet, communication software must use IP addresses when sending and receiving data. This process of mapping host domain names to IP addresses is called domain name resolution. Domain name resolution includes forward resolution (from domain name to IP address) and reverse resolution (from IP address to domain name). The domain name system of the Internet can transparently complete this work.
The mapping of Internet domain names to IP addresses is accomplished by a group of independent and cooperative domain name servers. The domain name server is actually a domain name service software. It runs on the specified machine to complete the mapping between domain names and IP addresses.
(1) Composition of domain name system
The domain name system consists of a parser and a domain name server.
① Parser: In the domain name system, the parser is the client. It connects with the application program and is responsible for querying the domain name server, explaining the response returned from the domain name server, and transmitting information to the application program.
② Domain name server: The domain name server is used to store domain name information. Part of the domain name information forms a zone. The domain name server is responsible for storing and managing one or more zones. In order to improve the reliability of the system, the domain name information of each zone is saved by at least two domain name servers.
(2) Working process of domain name system
A domain name server cannot store the names and addresses of all computers on the Internet. Generally speaking, the server only stores the computer name and address of a company or organization. For example, when a computer user in China needs to communicate with a computer named www of Massachusetts Institute of Technology, the user must first point out the name of that computer. Assume that the domain name address of this computer is "www.mlt.edu". Before communicating with the computer www, the application of this computer in China needs to know the IP address of ww,. In order to obtain the IP address, the application needs to use the Internet's domain name server.
① Suppose the parser sends a request to the local domain name server in China to find the IP address of "www.mit.edu".
② The local domain name server in China queries its own database first. If no relevant records are found, it sends a request to the root "." domain name server to search the IP address of "www.mit.edu"; The root domain name server returns a pointer information to the Chinese local domain name server and points to the edu domain name server.
③ China's Woody Domain Name Server sends a request to the edu domain name server to find the IP address of "mit. edu". The edu domain name server returns a pointer information to China's local domain name server and points to the "mit. edu" domain name server.
④ After the same resolution process, the "mit. edu" domain name server will return the IP address of "www.mit. edu" to the local domain name server in China.
⑤ The Chinese local domain name server sends the IP address of "www.mit.edu" to the parser.
⑥ The parser uses an IP address to communicate with www.mit.edu.
The whole process seems quite tedious, but because of the cache mechanism, the query process is very fast. From the above example, we can see that in order to get an address, a local domain name server often needs to find multiple domain name servers. Therefore, while searching for addresses, the local domain name server will also get information about many other domain name servers, such as IP addresses, responsible regions, etc. The local domain name server stores all this information together with the recently found host address in the cache for future reference.
(3) Domain name management of China's Internet
In order to adapt to the rapid development of the Internet, China has specially set up the "China Internet Network Information Center" and promulgated new regulations on China Internet domain names. On June 3, 1997, the Office of the Leading Group for Informatization Work of the State Council hosted the conference on the establishment of China Internet Network Information Center (CNNIC) and the release of the Interim Measures for the Registration of Internet Domain Names in China, announcing the establishment of China Network Information Center (CNNIC), CNNIC also issued the Interim Administrative Measures for the Registration of Internet Domain Names in China and the Implementation Rules for the Registration of Internet Domain Names in China. CNNIC is responsible for Internet domain name registration, IP address allocation, autonomous system number allocation, reverse domain name registration and other registration services in China, and will also provide relevant database services, relevant information and training services. As a non-profit management and service organization, CNNIC is responsible for making suggestions on the development, guidelines, policies and management of China's Internet, and assisting the Information Office of the State Council in implementing the management of China's Internet. This article was published in UEO Marketing website construction Company Shangpin China //ihucc.com/
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