What is a domain name? What website name? What is a URL?

What is a domain name?

 In reality, there are too many domain names to use, but do you understand the detailed meaning of domain names? Do you know what the domain name is? Below, Xiaobian will take you through the meaning of the domain name.

Domain name, I believe that everyone is not default, and has been used countless times! such as:

Google.com, baidu.com, 163.com, etc.

At this time, you may have to wonder why Xiaobian did not add www in front.

Because under normal circumstances, should not be www.baidu.com and the like?

Here, Xiaobian can tell you clearly, plus www, it is no longer a domain name!

Let us analyze the following paragraph:

Http://mail.163.com/index.html

1) http://: This is the protocol, which is the HTTP hypertext transfer protocol, which is the protocol for web pages to be transmitted over the Internet.

2) mail: This is the server name, which represents a mailbox server, so it is mail.

3) 163.com: This is a domain name, a unique name used to locate a website.

4) mail.163.com: This is the name of the website, consisting of the server name + domain name.

5) /: This is the root directory, that is, the server is found by the website name, and then the root directory of the web page is stored on the server.

6:) index.html: This is the default page in the root directory (of course, the default page of 163 is not this I don't know, but most of the default pages are index.html)

7) http://mail.163.com/index.html: This is called URL, Uniform Resource Locator, global address, used to locate resources on the Internet.

Maybe at this time, you still don't understand, what is the difference between this domain name and the website name?

OK, Xiaobian to tell you!

For example, you bought a university whose name is myname.com.

Then, you want to establish a language department, so the liberal arts building was established, called yuwen.myname.com

Then, you want to build a math department, OK, shuxue.myname.com is established.

Like 163, his domain name is 163.com, he wants to build a www server, so he has www.163.com.

He wants to play the mailbox server again, so mail.163.com also has it.

In this way, do you understand?

Well, just mentioned:

Http://mail.163.com/index.html

Among them, index.html is the default web page.

However, when we enter the URL, we usually enter it directly.

Mail.163.com or www.baidu.com, why is this?

Then look down.

Be aware that we can not only access files, but also access directories.

such as:

Http://www.163.com/

This means accessing the current root directory /.

If you don't know what the root directory is, please check Baidu. I won't go into it here.

At this point, the web server will check if it has this directory, OK, definitely. So, will the server return the entire directory to you? No!

The server will look for the default web page in its own directory, usually index.html, of course, you can modify it by configuring the web page. Xiaobian built Apache under LINUX, there are configuration files specifically modified, you can also try.

After that, the server finds the index.html in the directory and returns it to the web browser.

Therefore, when we visit www.baidu.com, the browser will automatically add http:// to us and become http://www.baidu.com.

And Baidu's server, after receiving the request, will automatically add /, become:

Http://www.baidu.com/.

Then, Baidu server will look for index.html or other default webpages in this directory, which is Baidu's homepage. After it is found, it will be returned to you through the http protocol. That is the Baidu homepage you saw.

The new "wave" of the global Internet:

The new "wave" of the global Internet:

The United States officially renounced the rights to administer domain names.

The world's Internet changed, an important event occurred these two days: the US government. UU It officially transferred the administration of Internet domain names to the non-profit organization ICANN (Internet Corporation for Assigned Names and Numbers). This is also a rare "change" in the Internet infrastructure.


What is the domain name?

To understand "domain management rights", we must first understand some basic terms of the Internet and have a certain understanding of the basic functioning of the Internet. "Domain name" is actually a string of names separated by periods. It is also the name of a computer or group of computers on the Internet. It is used to identify the electronic orientation (sometimes called geographical location) of a computer during data transmission. This is followed by another term "DNS (Domain Name System)" which is closely related to the domain name. In the complicated Internet, the domain name is like a "map", which tells each computer to find the target's route, but unfortunately there are too many destinations. In the end, people store this information hierarchically in servers of domain names of all sizes in the world. After entering the domain name and returning the car, the computer will contact these servers and finally get the actual digital address of the destination computer.

It seems that we do not care, but if you type "DNS failure" in the search engine, you will find many news: "failure of the large-scale network of Shandong Unicom, large-scale failure of Sichuan Telecom, etc." The most serious was to count the DNS failures nationwide that occurred in China at the end of January 2014. At that time, the failure lasted more than an hour and national 2/3 websites could not be opened normally, affecting tens of millions of Internet users. The domain name service is a seemingly simple but extremely important part of the Internet. In case of failure, several web services, email services and routing services will face embarrassment.

Existing domain name system and ICANN

Ollowing restoration of domain names to the Apartment's IP addresses, people no desafío infección (habitaciones), Spaces for each URL. Keeping all this data locally seems to be the easiest way to handle it, but it is not practical. On the one hand, the TCP / IP protocol itself uses a stack architecture to accommodate an almost unlimited number of addresses in a limited number of IP addresses. 

This practice of nesting TCP / IP or other networks in a global TCP / IP network greatly extends the extensibility of the network, but also complicates "Internet maps". 

The final solution is the current operation of the Internet domain name system: the user enters the domain name after the browser enters the domain name, such as www.ifanr.com, the computer will begin to try to find the address Input URL corresponding to the URL; The DNS server makes a request to consult the corresponding IP of www.ifanr.com. The DNS server checks its own local cache. If there is a record, it returns directly. 

However, if the local cache record may be outdated or does not exist, then the domain name must be re-executed. The query, at this time, the DNS server will initiate a query request to the root domain name server, the root domain name server will return the address of the authorized domain name server of the .com domain; DNS will again issue a query request to the authorized domain name server of the .com domain, and finally you will get www.ifanr. IP address data Com; Finally, the browser can download the latest data from the love fan server and display them in front of the user. It can be said that it is due to the configuration of the domain name and DNS that the Internet exists and is popular.

The non-profit organization ICANN is the actual administration and maintenance of the DNS. The official goal is: "To further internationalize the DNS system, introduce new top-level international domains (such as .com.org, etc.) and also manage the most important." Root nameserver. Profit does this, as if there were no problem, but this is not the case, ICANN is responsible for the assignment of Internet domain names and IP addresses, but ICANN was created due to the proposal of the NTIA of the Department. US Commerce Department, which proposed "strengthening the administration of network domain names and address technologies", also known as the "Green Book." In February 1998, it was written in the Federal Register , an important internal publication of the government of the United States Soon, ICANN was formed on September 30, 1998 and has since signed a contract with the United States Department of Commerce. domain, IP address and general agreement through its own organization, IANA (Internet Digital Distribution Authority).

Although ICANN is nominally an "administrator," the ICANN administration of the DNS system and the IANA functions are subject to US government contracts. UU To execute the instructions issued by the upper level, and Verisign carries out the specific implementation. In 2006, ICANN approved a note to allow the US Department of Commerce to UU Monitor some of your operations. In 2009, ICANN again signed an agreement with the US Department of Commerce. UU., Including the attempt to establish a "multi-stakeholder governance model", but did not eliminate the supervision and control of the US Department of Commerce. UU Finally, on March 10 of this year, ICANN and the United States Department of Commerce finally signed an agreement to eliminate all controls and supervision. Since October 1, two days ago, ICANN and IANA were completely transformed into independent non-profit organizations. Although the independence of ICANN and IANA have become a reality, the process has not been easy. Previously, the Attorneys General of the four US states. UU They asked federal judges to issue an emergency restraining order to prevent the Obama administration from relinquishing the federal government's right to administer Internet domain names. The final judge rejected the request on September 30, one day before the entry into force of the independent agreement. The United States Senate Cruz, who had previously run for president, issued a statement: "Jim, like Jimmy Carter, delivered the Panama Canal, Obama is now giving up the Internet."

At the end of 2014, Sina Technology interviewed the president of ICANN, Chehad, and publicly declared:

The main objective of ICANN is to make the entire Internet, made up of innumerable websites directed to a domain, a whole, not a division. The Chinese government will also enjoy the same voice and will help ICANN move forward in the global Internet industry. In addition to the Chinese government, Chinese companies, Internet companies and other users must participate. But this is an opportunity and means responsibility. Because we enjoy the benefits of the Internet, we must also participate in Internet governance. Undoubtedly, these years of operation of ICANN's Internet domain name services have maintained the stable functioning of the Internet. As ICANN becomes the "multi-stakeholder government" of the "independent government" of the United States, more new "conflicts" will be introduced. For example, in the past, the United States could rely on its own "Internet administrator" to outperform other countries on the Internet. However, after that, ICANN may "request" the revocation of the United States domain name in reverse in accordance with the request of other countries. At the moment, other countries can only block IP requests to US websites from their own servers. Whether "independence" will lead to the "domain name competition" of the Internet between countries has always been the most important question. Trump, the next presidential candidate of the United States, made it clear that he was opposed. Will ICANN unlock the chains of free and inclusive Internet or will it introduce war? This is still an unknown number. However, what is certain is that the Internet that has become the "second world" can not be controlled by a single country, but must be in the hands of all human beings.

What does hosting server mean?

What is the meaning of server hosting?

I think there are still many friends that I do not understand. Today, Xiaobian presents the advantages of server hosting, which details the most common types of server hosting and other common problems.

Hosting server is what it means?

Server hosting is an infrastructure delivery model that provides IT users with remote access to server resources (CPU, memory, disk, etc.) to drive applications and storage data without having to buy, configure and maintain server hardware. . Server hosting refers to the maintenance of external management and hardware resources specified for the use of the company. By paying a service fee to a hosted service, the company can obtain full server resources without paying for equipment maintenance and labor costs.


Is it selected to host the server?


Server hosting has many benefits, including faster shelves, more affordable prices, professional technical services and complete computer room facilities.

1. Set faster

The traditional process of ordering and sending servers to your office or data center usually takes weeks or even months. However, in many cases, managed service providers can implement, configure and make services accessible within a few minutes of placing the order. A shorter implementation time means bringing business services to market faster.

2. Monthly payment

Server hosting allows you to avoid large capital expenditures for hardware that depreciates over time. Instead, you only need to pay a monthly server hosting fee to access resources remotely. These payments include crack fixes and other important aspects of server hosting, such as space used by the server, power and cooling. Monthly payments also include the use of bandwidth.

3. Continuous maintenance.

Server hosting also eliminates the burden of worrying about all the work needed to keep the server running uninterrupted throughout the year, such as management, power, cooling, security, hardware repair, software updates, and more. This provides support for IT users. It's time to focus on important projects, not on secular tasks that keep the server running.


What are the different types of hosting servers?

There are many different types of delivery models managed by the server designed to help IT users and businesses achieve varying degrees of technical and financial results. The following are the most common:

Shared host

Shared hosting is a cheap way to host simple and low traffic websites and blogs. Server resources are divided into smaller shared hosting plans to provide users with a simple way to exist. There may be hundreds or thousands of shared hosting accounts on a single server, depending on how the hosting provider configures it. All accounts share server resources.

VPS Host

A VPS host is similar to a shared host, but in this case, the server resources are dedicated to specific accounts to minimize the risk of resource containment and degradation services for certain users. The VPS account on a single server is usually less than the VPS account on a shared host. As traffic and resource demands increase, users tend to "graduate" from shared hosting to VPS.

Dedicated hosting server

As the name implies, the hosting of dedicated servers gives users full access to all resources on a single dedicated server. There are no other clients on this server. The choice of a dedicated hosting server offers many advantages, such as full control of resources, improved security and access to the root. Dedicated server hosting is the next step in VPS hosting, since it allows clients to support applications of great importance to the mission and resources.

Accommodation in the public cloud

With the introduction of virtualization, hosting in the public cloud is most often associated with companies such as Alibaba Cloud, Tencent Cloud, NetTime Cloud and Huawei Cloud. In summary, public cloud hosting provides on-demand and self-service access to computing and storage resources over the Internet in a multi-tenant environment. By using virtualization technologies such as VMware, Hyper-V, Xen and KVM, public cloud hosting provides a redundant and scalable way to create large hosting environments that can be expanded or reduced at any time.


Private accommodation in the cloud

Like dedicated hosting, private cloud hosting dedicates all server resources in a private cloud to a single client. Think of a private cloud as a set of dedicated servers that are virtualized to provide a large amount of resources that can be managed as needed. Private clouds include all the benefits of a public cloud, such as redundancy and self-service access, but without the shared attributes of a multi-tenant environment. Hosting a private cloud provides an inherent security advantage because it is a unique tenant and also eliminates the risk of noisy neighbors problems.


Hybrid cloud hosting

Hybrid hosting will enter the market when complex distributed data and applications require multiple managed deployment models. This can combine hosting of dedicated servers with public hosting in the cloud or public hosting in the cloud and public hosting in the cloud. Hybriding uses several delivery models to achieve business infrastructure goals with the highest performance and the most cost-effective way.

Accommodation space

If you already have a server but you need space, energy and cooling to keep it running, accommodation can be a good option. The hosting offers greater perimeter security than most customers and is more reliable in terms of uptime, as data center providers must have strict requirements for power and cooling redundancy.

Is the hosting server safe?


All types of hosting servers have different levels of security, whether shared, private, public or hybrid.

Often, hosting the server is safer than trying to maintain and protect the servers or servers in your location. This is because server hosting providers have taken rigorous measures to ensure security and multiple layers, starting with the physical compilation where the server is located. Most data centers have strict access controls, from the doors around the building to the data center floor: armed guards, video surveillance, secure access control and more.

In addition, there are steps you can take to further protect the managed server environment up to the application layer.

What is the server hosting rate?


The cost of hosting the server is usually customized according to the user's needs. The different time limits of accommodation and cabinets are different and the price is different. There are hundreds of tens of thousands of casualties. I suggest you host it on request.

What is a DNS server?

People who have basically been exposed to knowledge related to the network should have heard the term DNS.

Because it is very important, it plays an important role in our online process: "resolve the URL / domain name to an IP address".

If an unreasonable DNS server is configured, it can cause the speed of the network to be slow and the website to open. Some malicious DNS will also cause an ad popup on your computer, a hijacked modification of the website (man attack in the middle), monitoring, etc.

Safety issue Therefore, to stabilize high-speed Internet, I have deliberately compiled global and reliable public DNS service addresses that are currently available worldwide.

The full DNS name is Domain Name System or Domain Name Service. Its main function is to "translate" known URLs (domain names) to IP addresses that computers can understand. This process is called DNS domain name resolution.

For example, Baidu's baidu.com is a domain name that everyone can easily remember, but the computer can not find the website server directly through the domain name. Because on the Internet, network devices can only rely on IP addresses (equivalent to the house number on the Internet) to address and position to establish a connection.

Therefore, the DNS server itself must maintain sufficient stability for a long time. The resolution of domain names must be fast enough and the speed and stability of your Internet access can be guaranteed. Once the DNS server "has a problem", such as its own failure, or the ability to resolve the URL of the IP address, the resolution is particularly slow, or resolving the incorrect IP address, etc., it will lead to a variety of Internet users Do not open the website, slow down the Internet and other incurable diseases.

And the quality DNS service is not only a fast resolution of domain names, but also some such as blocking malicious URLs, intelligent error correction, DNS contamination solution and accurate analysis of CDN to the IP node more close to you (which greatly improves the file). Download speed) and other functions.

DNS servers are generally financed by Internet service providers (ISP), such as telecommunications / mobile broadband. They have established multiple sets of DNS servers across the country. They are automatically assigned to you by region when you dial the Internet. In general, you can ignore them. Normal access to the internet However, the problem is that the DNS provided by some regions is often time of inactivity, overcrowding, does not expand timely, and the Internet is solved slowly when the Internet reaches its peak. Even the staff of the local computer room abuses their powers to obtain personal benefits, uses DNS to hijack websites, secretly inserts ads / induction / inhalation accounts. Passwords, etc., will affect the speed of the network and the online experience and the security of the user's account.

In short, if you are unstable on the Internet, trying to replace a group of DNS faster, more stable, cleaner, more secure and without hijacking can solve the problem. Fortunately, in addition to the broadband provider's DNS, large Internet companies such as Alibaba Cloud, Tencent Cloud, Google, Baidu, IBM, CNNIC, etc. They are also very generous to provide the public with a free DNS resolution server. Xiaobian has compiled a list of these addresses of reliable, free and high speed public DNS servers around the world for you to choose from.

The following collections are the IP addresses of the most reliable free public DNS services currently available worldwide (most nationally). Due to regional differences, the performance of the same group of DNS servers in different countries and regions is not exactly the same, resolution speed, response time, etc. They are different, so it is recommended that you take the results of the automatic speed measurement as standard, and compare and choose.

DNS + public is a public DNS service owned by Tencent Cloud. With more than 80 national lines and 4 lines abroad, it has BGP Anycast technology and is the first public DNS resolution service in China that supports the Google ECS protocol (edns-client-subnet). It uses only one IP, but there are three cluster disaster tolerance and second-level automatic failover. The speed measurement data in most places in China are very good and worth recommending.

Public DNS +

IPv4 address

Preferred: 119.29.29.29

Ali Public DNS is a free recursive DNS resolution system launched by Alibaba Cloud. It is said to be a group of hundreds of servers around the world with sufficient bandwidth resources. The goal is to become part of the domestic Internet infrastructure, and is compatible with BGP Anycast and ECS technology.

AliDNS Ali Public DNS

IPv4 address

Preferred: 223.5.5.5

Wait: 223.6.6.6

114 DNS The number of users in China is quite large and their DNS resolution success rate is high. Compared to the DNS of the ISP, you can access more national and foreign websites; it is said to be pure, there is no kidnapping, it is not necessary to support forced publicity or vulgar websites. Pain; 114DNS is done before, it has a certain amount of accumulated technology, good stability, although the speed is a bit worse than the previous two, but it can also be satisfactory. It also has a function that allows you to select different DNS groups for different purposes.

114 DNS

Regular public DNS (clean and without kidnapping)

Preferred: 114,114,114,114, alternative: 114,114,115,115

Intercept the phishing virus trojan website (protect the Internet)

Preferred: 114,114,114,119, waiting: 114,114,115,119

Block pornography sites (protect children)

Preferred: 114,114,114,110, replacement: 114,114,115,110

Public DNS resolution service of Baidu, support ipv4 and ipv6. As the largest search engine in China, Baidu has first-class infrastructure and high technical capacity, and domestic speed is quite fast! The service is fast and stable without hijacking, intelligently intercepts malicious websites and is compatible with BGP Anycast and ECS technologies.

Baidu BaiduDNS

IPv4 address: 180.76.76.76

IPv6 address: 2400: da00 :: 6666

The DNS Cake is a free public DNS resolution service of 360. It can make browsing more stable, faster and safer, block phishing websites for families, filter out illegal websites, establish an environment online and healthy, and automatically correct the errors of the domain names.

DNS Cake

Preferred (Telecom / Mobile / Tietong): 101.226.4.6

Alternative (Telecom / Mobile / Tietong): 218.30.118.6

Preferred (China Unicom): 123.125.81.6

Alternative (China Unicom): 140,207,198.6

sDNS (SecureDNS, called sDNS) is a free public cloud resolution service launched jointly by the China Internet Network Information Center, CNNIC, and national and foreign telecommunications operators. Its objective is to provide users with high-speed, secure and intelligent Internet access resolution services. The recursive cloud resolution service sDNS uses IP Anycast + BGP technology to distribute distributed heterogeneous services between regions and operators, which is faster and more stable than the DNS provided by operators.

CNNIC sDNS

IPv4 address

Preferred: 1.2.4.8

Wait: 210.2.4.8

OneDNS is a secure, fast and free niche DNS service. It can block malicious websites and get rid of DNS contamination and unscrupulous ISP hijacking. Accelerate your network connection while the high-speed lines across the North and the South.

OneDNS

IPv4 address

Preferred: 117.50.11.11

Wait: 117.50.22.22

Recommendation of the free public DNS resolution service of EE.

As its name implies, foreign DNS is, of course, suitable for foreign users. For home users, although these DNS servers are not fast in China, they have many effects. For example, when you buy a foreign VPS to create related applications, you can configure it to use external DNS, etc.

Google's public global DNS free service is designed to improve the speed of web browsing and improve the browsing experience of web users. Basically, it is not necessary to make more presentations. It can be the public DNS most used nowadays in the world. It is antiquated, stable and powerful.

Google public DNS

IPv4 address

Preferred: 8.8.8.8

Wait: 8.8.4.4

IPv6 address

Preferred: 2001: 4860: 4860 :: 8888

Wait: 2001: 4860: 4860 :: 8844

CloudFlare DNS is known as the fastest DNS service in the world (of course, it is not global> _ <), CloudFlare is one of the largest CDN / DDOS protection service providers in the world (cooperating with Baidu Cloud Acceleration in China) The global infrastructure resources are extremely rich, and the capital and technical force are quite strong. The speed measured in foreign countries is quite strong. Currently, I have changed all VPS overseas to this DNS. The speed of resolution is very fast, which is worth recommending!

DNS CloudFlare

IPv4 address

Preferred: 1.1.1.1

Wait: 1.0.0.1

IPv6 address:

Preferred: 2606: 4700: 4700 :: 1111

Wait: 2606: 4700: 4700 :: 1001

Quad9's free public DNS service (9.9.9.9), released by IBM, Global Cyber ​​Alliance and Packet Clearing House, is an intelligent security blockade of malicious websites, botnets, phishing attacks and other associated domain names to malicious hosts, and more Protection of privacy. This set of DNS can be used by friends who need security.

IBM Quad9

IPv4 address

Preferred: 9.9.9.9

Wait: 149,112,112,112

IPv6 address

Preferred: 2620: faith :: faith

Wait: 2620: faith :: 9

You can set up a public DNS on your router, which will be applied to all your devices. It can also be configured independently on a specific computer or mobile phone, as needed. The configuration methods of Win, macOS, Linux and other systems can be easily searched.

And not only computers and mobile phones, game consoles such as XBox, PS4 or any network device, can basically configure DNS. If you play games and download them too slowly, try changing a DNS to see the effect.

What is a domain name?

What is a domain name? What name of the website? What is a URL?

What is a domain name? Actually, there are too many domain names to use, but do you understand the detailed meaning of domain names? Do you know what the domain name is? Next, Xiaobian will take you through the meaning of the domain name.


Domain name, I believe that everyone is not the default, and has been used countless times! For example:

Google.com, baidu.com, 163.com, etc.

At this time, you may need to ask yourself why Xiaobian did not add www to the front.

Because under normal circumstances, should not it be www.baidu.com and the like?


Here, Xiaobian can tell you clearly, in addition to www, it is no longer a domain name!

Let's analyze the following paragraph:

Http://mail.163.com/index.html

1) http: //: This is the protocol, which is the HTTP hypertext transfer protocol, which is the protocol for web pages to be transmitted over the Internet.

2) mail: This is the name of the server, which represents a mailbox server, so it is mail.

3) 163.com: this is a domain name, a unique name used to locate a website.

4) mail.163.com: this is the name of the website, which consists of the name of the server + the name of the domain.

5) /: This is the root directory, that is, the server is found by the name of the website and then the root directory of the web page is stored on the server.

6 :) index.html: this is the default page in the root directory (of course, the default page of 163 I do not know, but most of the default pages are index.html)

7) http://mail.163.com/index.html: This is called URL, Uniform Resource Locator, global address, used to locate resources on the Internet.

Maybe at this time, you still do not understand, what is the difference between this domain name and the name of the website?

Ok, Xiaobian I'll tell you!

For example, you bought a university whose name is myname.com.

So, you want to establish a language department, that's how the liberal arts building was established, called yuwen.myname.com

Then, you want to build a math department, OK, shuxue.myname.com was established.

Like 163, your domain name is 163.com, you want to build a www server, so you have www.163.com.

He wants to play again on the mailbox server, so mail.163.com has it too.

Well, I just mentioned:

Http://mail.163.com/index.html

Among them, index.html is the default web page.

However, when we enter the URL, we usually enter it directly.

Mail.163.com or www.baidu.com, why is this?

Then look down.

Keep in mind that we can not only access the files, but also the directories.

For example:

Http://www.163.com/

This means accessing the current root directory /.

If you do not know what the root directory is, check Baidu. I will not enter here.

At this point, the web server will check if it has this directory, OK, definitely. So, will the server return the full directory? Do not!

The server will search the default web page in its own directory, usually index.html, of course, you can modify it by configuring the web page. Xiaobian built Apache under LINUX, there are specifically modified configuration files, you can also try it.

After that, the server finds the index.html in the directory and returns it to the web browser.

Therefore, when we visit www.baidu.com, the browser will automatically add http: // to us and it will become http://www.baidu.com.

And the Baidu server, after receiving the request, will automatically add /, it will become:

Http://www.baidu.com/

Then, the Baidu server will search for index.html or other default web pages in this directory, which is the Baidu home page. Once it is found, it will be returned through the http protocol. That's the Baidu home page that you saw.

Finally, a great introduction to a book, the HTML books of HeadFirst, is very useful for beginners. If you want to learn a web page.

Domain name server

Parent element: Name server

This way of managing names is to assign different groups to the names of the subsystems. Each layer in the system is called a domain, and each domain is separated by a point.
The so-called domain name server (namely, Domain Name Server, called Name Server, DNS) is actually the host with the domain name system. It is a hierarchical database that performs name resolution.

DNS can allow a name server to "delegate" a part of its name service (a known zone) to a secondary server to implement a hierarchical namespace. In addition, the DNS provides additional information, such as system aliases, contact information, and the host that acts as a mail center for a group or system domain.

Currently, the limit for the length of each domain name is 63 characters, and the total length of the domain name can not exceed 253 characters. Domain names are also limited to a subset of ASCII characters, which means that many other languages ​​can not correctly represent their names and words. Based on the IDNA system based on the Punycode code, Unicode strings can be assigned to a valid DNS character set, which some records have validated and adopted as an alternative solution.

In addition, there is no distinction between upper and lower case in the domain name. The domain name generally can not exceed level 5, the domain level from left to right becomes higher and the top-level domain contains a lower-level domain.

The domain name is unique on the Internet.
When the advanced subdomains are the same, low-level subdomains are not allowed to duplicate. A server can only have one IP address, but it can have several domain names.

The domain name is the "second generation" of network addressing. The URL is an abbreviation of Uniform Resource Location, translated as "Uniform Resource Locator".
The DNS system is managed by a wide variety of DNS software, including:
BIND (Berkeley Internet Name Domain), which is the most widely used DNS software.
DJBDNS (DNS implementation of Dan J Bernstein)
MaraDNS
NSD (name of the daemon server)
PowerDNS

Any computer network that uses IP can use DNS to implement its own private name system. However, the term "domain name" is the most used when referring to domain names implemented in Internet public DNS systems.
This is based on 13 global "root servers", with the maintenance organization in addition to three of them, all located in the United States. Starting with the 13 root servers, the remaining Internet DNS namespaces are delegated to other DNS servers that provide specific portions of the DNS namespace.

The "owner" of a domain name can be found by consulting the whois database; for most gTLDs, ICANN maintains the basic WHOIS, and the domain registrar that controls that domain maintains the WHOIS details. For domain registrations with more than 240 national domain names (ccTLD), the respective country maintains its WHOIS.

The current methods of DNS system control are often blamed. The most frequently targeted focus is the abuse of DNS by monopolistic or quasi-monopolistic companies, such as VeriSign, and the distribution of top-level domains.

Others claim that many DNS server software does not work well for dynamic IP allocation, although this is a bug of some specific implementations instead of the protocol itself.
DNS uses TCP and UDP port 53.