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Every time I open a page on the Internet, there is a share of DNS's credit.

Let's get to know it with the editor today.

Each computer has its own IP, unique and unique human communication, starting from knowing each other's names, such as Xiaofang and Xiaomei, which are easy to remember.

However, if you meet someone with a duplicate name, you have to make a careful distinction. After all, the message to be sent to Liu Wei on the 12th is mistakenly sent to Liu Wei on the 35th, which will be more embarrassing.

The computer kingdom is a world of numbers, and each computer can represent itself with unique numbers, perfectly avoiding the annoyance of duplicate names. This unique number is generally called the IP address.

Currently, there are two types of IP addresses:

IPv4IPv4 is the fourth revised version in the process of Internet protocol development. it is the most widely used version and the core of the Internet. IPv4 is a 32-bit binary number, that is, a 32-bit string of numbers consisting of 0 and 1, representing 4294967296 addresses and nearly 4.3 billion IPv4 addresses.

To facilitate memory, these 32-bit zeros and ones can also be displayed in decimal. The most commonly used is 192.168.1.1.

Format of the IPv4 address, as shown in the following figure.

In the early days of the Internet, it was absolutely sufficient for each computer to be assigned an IPv4 address.

However, there are some things that always exceed people's expectations.

As a result of the rapid development of the Internet, 4.3 billion IPv4 addresses around the world have been allocated by the end of December 2019.

Smart people have also adopted some technical methods to alleviate the depletion of IPv4 addresses, such as:

Recycling IPv4 addresses: the Internet number assignment Office (IANA) and the Regional Internet Registry (RIR) will recycle and reallocate large chunks of IPv4 addresses allocated during the early days of the Internet.

Dynamic IPv4 address: through DHCP technology, in a local area network, dynamically assign an IPv4 address to each computer that boots into the local area network, and when a computer shuts down and exits the local area network, an IPv4 address is recovered and assigned to a new computer.

Internal and external network IPv4 address: through NAT technology, a local area network is assigned a valid IPv4 address in the Internet, which is called the external network address. The IPv4 addresses of all computers in this local area network are called intranet addresses. When communicating between each computer in the local area network, the internal network address is used; when a computer in the local area network communicates with a computer outside the local area network, the external network address of the local area network is used.

IPv6IPv6 is the sixth revised version of the Internet protocol development process, designed by the Internet Engineering Task Force (IETF), the biggest use is to replace the IPv4 address. IPv6 is a 128-bit binary number, that is, a 128-bit number string consisting of 0 and 1, representing 340282366920938463463374607431768211456 addresses.

With a number as long as 39 digits, people do not know how to use scientific counting to accurately explain its units. In short, there are countless IPv6 addresses, and it claims to be able to assign an IPv6 address to every grain of sand in the world.

To facilitate memory, these 128-bit zeros and ones can also be displayed in hexadecimal. The most commonly used one is ABCD:EF01:2345:6789:ABCD:EF01:2345:6789.

The IPv6 address here is divided into eight segments, separated by ":" between different segments, each with a 16-bit hexadecimal number string.

Format of the IPv6 address, as shown in the following figure.

IP is too difficult to remember, and the domain name to help IP address is so unique, so when we surf the Internet, do we have to enter the IP address of this server in order to open web pages and videos in a certain server?

Of course not.

As mentioned earlier, computers use IP addresses to represent themselves. Human beings, of course, it is more convenient to use names!

The URL address we enter in the browser, such as www.zte.com.cn, is actually a name, generally called a domain name.

Don't underestimate this short name, it contains a lot of content, let's take a closer look at it.

From right to left, they are:

Cn: top-level domain name, cn represents China, there are other ".com for business organizations", ".edu for universities", ".uk for Britain" and so on.

Com: second-level domain name.

Zte: a domain name that belongs to a company.

Www: a third-level domain name that indicates what service a company provides. Www represents an ordinary web page and mail represents an email address.

IP or domain name, you have to find DNS to help access the Internet, is a process of finding IP according to the domain name.

Domain name system (Domain Name System, abbreviation: DNS) is a service of the Internet. DNS, as a distributed database that maps domain names and IP addresses to each other, can make people more convenient to access the Internet.

When our local computers connect to the network, they will automatically assign the IP address of a DNS server, this DNS server is called the local domain name server, which is generally provided by the network service provider.

Enter a domain name in the browser, such as www.xyz.com, and click enter, and it's time for DNS to play a role.

At best, only three steps are required:

1. Local computer A sends a query message to the local domain name server DNS101 according to the IP address of the configured local domain name server: Hey, do you know the IP address of www.xyz.com?

2. Someone has just asked this domain name, and the local domain name server DNS101 has found the IP address and cached it, and will reply to the local computer A: you are lucky that the IP address you want to visit is 192.168.160.101.

3. After the local computer A receives the response, directly find the computer B of 192.168.160.101, and the web page of 192.168.160.101 can be displayed successfully in the browser.

In general, we have to query at least several times and look in several DNS before we can find the real IP address.

Now this kind of query "An ask B → B reply A → An ask C → C reply A → An ask D → the final A to D" is called iteration.

There is another way of query called recursion: "An ask B → B ask C → C reply B → B reply A → finally A to D."

The web page can't be opened, maybe it's the pot of DNS. Sometimes we can't open the web page, in fact, it may be that our computer can't find DNS.

Without DNS, the URL we entered cannot be converted into the real IP address of the web server, and of course we can't open the website.

Common reasons for DNS shutdowns include:

The corresponding relationship between the domain name stored in the contaminated DNS and IP, due to hacker attacks, data anomalies and other reasons, a domain name corresponds to the wrong IP address. In this case, if the computer wants to access website A through this DNS, it may be misled to website B.

The IP address of DNS that we configured on the local computer was modified, which was accidentally modified by other applications. In this case, the computer wants to visit website A, but cannot find the correct DNS.

Server crash DNS is a server that implements specific functions, is a professional high-performance server, and can crash in some cases. Once crashed, our computer wants to access the Internet through this DNS, it must have failed.

Records stored in invalid DNS, such as the correspondence between a domain name and an IP address, and the correspondence between a domain name and another domain name, all have a life cycle, for example, the TTL is 10 minutes. Once the time limit is exceeded, these correspondence are cleaned up and cannot be provided to the computer for query.

So what can we do to fix DNS?

In addition to waiting for DNS maintenance personnel to fix it, you can also try to modify the DNS address in your network settings on your local computer.

In the local PC, select Settings-- > Network and Internet-- > Ethernet-- > Network connection-- > IP configuration-- > Edit, select IPv4, enter the preferred DNS and alternative DNS, and click the Save button.

DNS servers provided by some large factories for fans' reference:

Google Public DNS:8.8.8.8 and 8.8.4.4

OpenerDNS:42.120.21.30

AliDNS:223.5.5.5 and 223.6.6.6

114DNS:114.114.114.114 and 114.114.115.115

Conclusion well, today is another day of learning, and useful knowledge has been increased.

Through today's article, we have learned:

There are two types of IP addresses: IPv4 and IPv6. IPv4 is the past and present, IPv6 is the trend and the future.

The URL address of a website contains four levels of domain names: top-level domain name, second-level domain name, third-level domain name and fourth-level domain name.

The working process of DNS is to find the domain name according to the domain name, the IP address according to the domain name, and the domain name according to the IP address.

Unable to surf the Internet, it may be the problem with DNS.

Ladies and gentlemen, if you encounter a network outage, remember to check the DNS information configured locally.

This article comes from the official account of Wechat: ZTE document (ID:ztedoc), author: ZTE document

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