您听说过DNS一词吗？您是否(Did)偶然发现了告诉您无法访问DNS 服务器的错误消息？(DNS server)您知道DNS是什么以及它的用途是什么吗？如果您想了解，请阅读本指南。我们解释了DNS是什么、它在互联网上的作用以及它是如何工作的。为了彻底，我们还将回顾一下它的历史。让我们开始吧：
什么是 DNS（域名系统）？
DNS代表“域名系统(domain name system)”，它是用于管理全球网站IP地址(IP address)的标准。在计算机语言中(computer language)，互联网上的每个网站都有一个可以找到的IP 地址。(IP address)例如，可以在IP 地址 104.26.13.188找到我们的(IP address 104.26.13.188)Digital Citizen网站。
计算机和其他设备在记住和使用无限数量网站的 IP 地址方面没有问题。然而，像你我这样的人很难做到这一点。最后，记住 digitalcitizen.life 比记住 104.26.13.188 这样的一系列数字要容易得多。这就是DNS 技术(DNS technology)存在的原因：
DNS的目的是将互联网上网站的 IP 地址转换为我们人类可读、易于理解和记忆的东西。
在某种程度上，您可以将DNS 技术(DNS tech)视为一个巨大的电话簿，它将名称与世界上每个网站的IP 地址(IP address)相关联。DNS与真实电话簿的区别在于，您拥有的不是电话号码，而是IP 地址(IP address)。我们记得朋友的名字是正常的，但不记得他们的电话号码。当您想打电话给您的一位朋友时，您只需打开智能手机上的电话簿并按他们的名字呼叫他们。
就像您不必记住朋友的电话号码一样，您不必记住网站的 IP 地址即可访问它们。您只需要记住它们的名称，DNS 技术(DNS technology)会自动将它们与正确的 IP 地址相关联。
DNS如何工作？
现在您知道DNS代表什么以及它的作用了。但它是如何做到的呢？答案是：DNS通过(DNS)DNS 服务器(DNS servers)完成其工作。它们是特殊的服务器，用于存储来自 Internet 的各种网站的 IP 地址的大型数据库，以及执行相同操作的其他DNS服务器的 IP 地址。(DNS)
当您想访问一个网站时，您的计算机或设备会询问其 DNS 服务器是否知道该网站的 IP 地址。(When you want to visit a website, your computer or device asks its DNS server if it knows the IP address of that website.)如果确实如此，并且您的计算机收到了答复，您将立即被转发到该网站的IP 地址(IP address)。这个过程称为DNS 查找(DNS lookup)。这就像智能手机电话簿上的搜索功能。(search function)
但是，您的计算机或设备(computer or device)上设置的DNS 服务器(DNS server)可能不知道您尝试访问的网站的IP 地址。(IP address)这是可能发生的事情，因为维护一个包含世界上所有网站的数据库是一项艰巨的任务。但是，DNS 服务器(DNS server)并不是网站海洋中的孤岛：它们之间也相互连接，并且还保持着层次结构。如果 DNS 服务器不知道某个网站的 IP 地址，它会将问题转发给(If a DNS server doesn't know the IP address of a certain website, it relays the question to another DNS server)层次结构中更高的另一个 DNS 服务器。找到结果后，会将响应转发回您的计算机或设备(computer or device)。
整个“询问和响应(ask and respond)”过程发生在几毫秒内。它是如此之快，以至于您不知道哪个DNS 服务器(DNS server)已经转发了您尝试访问的网站的IP 地址。(IP address)然而，现代计算机、设备和应用程序不喜欢任何延迟，即使它可能很小，所以它们中的大多数还保留其DNS请求的缓存。这样，他们可以在您下次访问时更快地打开您已经访问过的网站。
如果您想知道谁维护DNS服务器，您应该知道此类服务器由一系列不同的实体维护，从您的ISP（互联网服务提供商(Internet Service Provider)）到来自世界各地的政府组织和大学。
在本文前面，我们简要提到过DNS服务器不仅在它们之间进行通信，而且它们还具有一个层次结构。这句话可能让您很想知道哪个DNS服务器是“山中之王”。🙂 这是答案：有 13 个国王，这意味着世界上所有的DNS服务器都中继(world relay)到这 13 个主要的 - “食物链(food chain)的顶端” - DNS服务器。它们还带有DNS 根服务器(root servers)的名称。
但是，不要假设那里只有 13 个物理根服务器。实际上，这些根DNS服务器中的每一个都使用冗余网络设备(network equipment)，并且在地理上分布在多个位置，因此如果其中一个物理DNS服务器出现故障，互联网也不会出现故障。更准确地说，有 13 台根服务器由 12 家运营商（它们是独立的组织）维护，全球共有 1038 个实例（也称为物理DNS 根(DNS root)服务器）。
如果您想知道谁维护它们以及它们的地理位置，您可以在Wikipedia - Root name server和root-servers.org上找到该列表。剧透警告(Spoiler alert)：大多数根DNS运营商来自(America)美国(United) 。(States)
DNS 是什么时候发明的，由谁发明的？
DNS 或域名系统是由一个叫 Paul Mockapetris 的人在 1983 年发明的。(DNS or Domain Name System was invented by a man called Paul Mockapetris, back in 1983.)在此之前，互联网几乎不存在。然而，作为ARPANET一部分的计算机，由(ARPANET)ARPA（高级研究(Advanced Research)计划(Projects)局(Agency)，来自美国国防部(United)）(Department)创建(States)和维护的(Defense)计算机网络(computer network)，都依赖数字地址在它们之间进行通信。阿帕(ARPANET)网是我们今天所知的互联网的基础之一。ARPANET中主机的数字地址 是手动添加的，最初存储在一个HOSTS.txt 文件(HOSTS.txt file)中，用于将它们翻译成人类可读的名称。
然而，只使用HOSTS.txt文件很快就会变得太慢，因为主机（计算机）的数量正在增加。这个问题的解决方案来自Paul Mockapetris，他必须发明一种方法来让网络更容易被人们使用。换句话说，他必须找到一种为数字分配名称的方法，这样人们就不必为他们所连接的所有计算机学习数字地址。
于是，DNS出现了：一种将命名职责划分到多个服务器的系统，这些服务器位于网络的不同位置。域名系统(Domain Name System)具有很大的优势，即即使某些服务器出现故障，也能够提供答案（将名称转换为数字地址），因为仍在工作的其他服务器可以提供相同的功能。
您想了解更多关于DNS的信息吗？
如果您对此问题的回答是“是”(Yes)，那么我们随时准备提供帮助。多年来，我们发布了很多与DNS相关的教程和指南。如果您渴望学习，请随意浏览列表：
- 在Windows 10(Windows 10)中更改DNS设置的3 种方法
- 我的DNS是什么？在Windows 10(Windows 10)中查找的 5 种方法
- 什么是第三方DNS 服务器(DNS server)？使用公共DNS 服务器(DNS server)的8 个理由
- 什么是基于HTTPS的DNS或安全 DNS 查找(HTTPS or Secure DNS lookups)？在谷歌浏览器(Google Chrome)中启用它！
- 如何在Firefox中启用(Firefox)基于 HTTPS(HTTPS)的DNS
现在您对DNS(DNS)有了更多的了解。你还有什么想学的吗？
既然您已经了解了DNS 技术(DNS technology)的基础知识及其工作原理，那么您应该可以更轻松地了解在浏览 Internet 时遇到的某些问题。如果您对DNS(DNS)有任何疑问或想分享有关DNS服务器的更多信息，请随时在下面的部分中发表评论。
What is DNS? How is it useful?
Have you heard of the term DNS? Did you stumble upon error messageѕ that told you that the DNS server could not be reached? Do you know what a DNS is and what its purpose is? If you want to find out, read this guide. We explain what DNS is, its role on the internet, and how it wоrks. To be thorough, we're also going to go through a bit of its hіstory. Let's get started:
What is DNS (Domain Name System)?
DNS stands for "domain name system," and it is a standard used for managing the IP addresses of websites all over the world. In computer language, every website on the internet has an IP address where it can be found. For instance, our Digital Citizen website can be found at the IP address 104.26.13.188.
Computers and other devices have no issues in remembering and using IP addresses for an unlimited number of websites. However, people like you and me have a hard time doing that. In the end, it is so much easier to remember digitalcitizen.life than it is to remember a series of numbers like 104.26.13.188. That's why the DNS technology exists:
The purpose of DNS is to translate the IP addresses of websites on the internet into something readable, easy to understand and remember for us humans.
In a way, you could look at the DNS tech like a huge phonebook that associates a name with every website IP address in the world. The difference between DNS and a real phonebook is that instead of phone numbers, you have IP addresses. It is normal for us to remember our friends' names, but not their phone numbers. When you want to call one of your friends, you just open the phonebook on your smartphone and call them by their name.
Just like you don't have to remember your friends' phone numbers, you don't have to remember the IP addresses of websites in order to be able to visit them. All you need to remember is their names, and the DNS technology automatically associates them with the correct IP addresses.
How does DNS work?
Now you know what DNS stands for and what it does. But how does it do what it does? The answer is: the DNS does its job through DNS servers. They are special servers that store large databases of IP addresses of various websites from the internet, as well as the IP addresses of other DNS servers that do the same thing.
When you want to visit a website, your computer or device asks its DNS server if it knows the IP address of that website. If it does and your computer receives an answer, you are immediately relayed to that website's IP address. This process is called DNS lookup. It is like the search function on your smartphone's phonebook.
However, it is possible that the DNS server set on your computer or device doesn't know the IP address of a website that you are trying to visit. It's something that can happen because maintaining a database with all the websites in the world is a titanic task. However, DNS servers are not lost islands in a sea of websites: they are also connected among themselves and they also maintain a hierarchy. If a DNS server doesn't know the IP address of a certain website, it relays the question to another DNS server, that is higher in the hierarchy. When a result is found, the response is forwarded back to your computer or device.
This whole "ask and respond" process happens in milliseconds. It is so fast that you don't get to know which DNS server has relayed the IP address of the website that you are trying to visit. However, modern day computers, devices, and apps don't like any delay, as small as it might be, so most of them also keep caches of their DNS requests. That way, they can open a website you've already visited even faster the next time you visit it.
If you're wondering who maintains DNS servers, you should know that such servers are maintained by a whole range of different entities, starting from your ISP (Internet Service Provider) to governmental organizations and universities from all over the world.
A bit earlier in this article, we briefly mentioned that DNS servers are not only communicating among themselves, but they also have a hierarchy put in place. This statement probably made you curious to find out which DNS server out there is the "king of the hill." 🙂 Here's the answer: there are 13 kings, meaning that all the DNS servers in the world relay to these thirteen main - "top of the food chain" - DNS servers. They also bear the name of DNS root servers.
However, don't assume that there are only 13 physical root servers out there. In reality, each of these root DNS servers uses redundant network equipment, and are spread geographically in multiple locations, so that if one of the physical DNS servers goes down, the internet does not. To be more precise, there are 13 root servers maintained by 12 operators (which are independent organizations), and there are 1038 instances (aka physical DNS root servers) all over the world.
If you want to know who maintains them and where they're geographically located, you can find the list on Wikipedia - Root name server and root-servers.org. Spoiler alert: most of the root DNS operators are from the United States of America.
When was DNS invented, and by whom?
DNS or Domain Name System was invented by a man called Paul Mockapetris, back in 1983. Before that, the internet pretty much didn't exist. However, the computers that were part of ARPANET, a computer network that was created and maintained by ARPA (Advanced Research Projects Agency, from United States' Department of Defense), all relied on numerical addresses to be able to communicate between themselves. ARPANET was one of the foundations on which the internet as we know it today was built. The numerical addresses of the hosts in ARPANET were added manually and were initially stored in a HOSTS.txt file that was used to translate them into human-readable names.
However, using only that HOSTS.txt file soon became too slow, as the number of hosts (computers) was adding up. The solution to this problem came from Paul Mockapetris, who had to invent a way to make the networks easier and more friendly to use by people. In other words, he had to find a way to assign names to numbers, so that people wouldn't have to learn numerical addresses for all the computers to which they connected.
And so, DNS appeared: a system that divides the naming responsibilities across multiple servers, found in different places on the network. The Domain Name System had the great advantage of being able to provide answers (translating names to numerical addresses) even if some of the servers went down, as the others that were still working could provide the same functionality.
Would you like to learn more about DNS?
If you answered Yes to this question, then we're ready to help. Over the years, we've published quite a few tutorials and guides related to DNS. If you're eager to learn, feel free to browse through the list:
Now you know more about DNS. Is there anything else you'd like to learn?
Now that you know the basics of what the DNS technology is and how it works, you should have an easier time understanding certain issues you stumble upon when browsing the internet. If you have any questions about DNS or you would like to share more information about DNS servers, do not hesitate to leave a comment in the section below.
