Start from scratch to teach you common DNS troubleshooting methods

In actual application, DNS resolution errors may occur, that is, when we access a domain name, it cannot be resolved to an IP address, however, you can directly enter the website IP address for normal access, which is caused by a DNS resolution failure. This phenomenon has a high probability of occurrence, so this article will teach you some basic DNS troubleshooting methods from scratch.

1. What is a DNS resolution fault?

Generally, www.51cto.com is called a domain name. As we all know, any host on the network is identified by an IP address. That is to say, only the IP address of the website can be successfully accessed.

However, because the IP address information is not easy to remember, the domain name is displayed on the network. During access, we need to enter this domain name that is easy to remember, there will be a server in the network that automatically resolves the corresponding domain name to an IP address. This is the DNS server. The machine that can implement DNS resolution can be either its own computer or a computer in the network. However, when DNS resolution fails, for example, resolving a domain name into an incorrect IP address, or, if we do not know the IP address corresponding to a domain name, we cannot access the site through the domain name. This is a DNS resolution failure.

The biggest symptom of a DNS resolution failure is that the IP address corresponding to the website is correct, but an error occurs when accessing the domain name.

Ii. How to Solve DNS resolution faults:

When a DNS resolution fault occurs on our computer, don't worry. The solution is also simple.

(1) Use nslookup to determine whether a DNS resolution fault is true:

To fully determine whether a DNS resolution fault exists, you must use the NSLOOKUP provided by the system.

Step 1: confirm that your system is windows 2000 or above, and then press Start> RUN> Enter CMD to enter the command line mode.

Step 2: Enter the nslookup command and press enter to go To the DNS resolution query page.

Step 3: the command line window displays the DNS server address used by the current system. For example, the IP address of the author's DNS server is 202.106.0.20.

Step 4: Enter the domain name of the site you cannot access. For example, if I enter www.softer.com and cannot access it, DNS resolution may fail. We will receive a prompt message for DNS request timed out and timeout was 2 seconds. This shows that our computer does have a DNS resolution fault.

TIPS: If the DNS resolution is normal, the correct IP address will be returned. For example, if I use the address www.sohu.com for query resolution, I will get the name: sohu.com, addresses: 61.135.133.103, 61.135.133.104 information.

(2) check whether the DNS server works properly:

In this case, we need to check the DNS address used by our computer and its running status.

Step 1: confirm that your system is windows 2000 or above, and then press Start> RUN> Enter CMD to enter the command line mode.

Step 2: Enter the ipconfig/all command to query network parameters.

Step 3: In the ipconfig/all display information, we can see a place where dns servers is written. This is the address of our DNS server. For example, the author is 202.106.0.20 and 202.106.46.151. It can be seen from this address that it is an Internet address. If an Internet DNS resolution error occurs, we can change the address of another DNS server to solve the problem.

Step 4: If the DNS server displays the internal network address of your company, it means that your company's DNS resolution work is handed over to the internal DNS server, in this case, we need to check the DNS server and perform the nslookup operation on the DNS server to check whether the resolution can be normal. The DNS service fault on the DNS server can be solved in general.

(3) Clear DNS Cache Information:

When a computer accesses a domain name, it does not need to seek help from the DNS server every time it accesses the domain name. Generally, after the resolution is completed, the resolution entry is saved in the DNS Cache list of the computer, if the DNS resolution changes at this time, the DNS Cache list information does not change, and the computer will not connect to the DNS server to obtain the latest resolution information when accessing the domain name, it will be resolved based on the cache correspondence saved on your computer, so that DNS resolution will fail. In this case, we should clear the DNS Cache command to solve the fault.

Step 1: Choose Start> RUN> Enter CMD to enter the command line mode.

Step 2: In command line mode, we can see in ipconfig /? There is a parameter named/flushdns, which is the command to clear DNS Cache Information.

Step 3: run the ipconfig/flushdns command. When the prompt "successfully flushed the dns resolver cache" appears, the cache information of the current computer has been cleared successfully.

Step 4: When we access the domain name again, we will get the latest resolution address on the DNS server, and there will no longer be a resolution error caused by the previous cache.

(4) modify the HOSTS file method:

The modification of the HOSTS method is to modify the DNS resolution correspondence in the HOSTS file to achieve correct resolution. When accessing a domain name on the local computer, the HOSTS file in the Local System will be checked first. The priority of the Resolution relationship in the HOSTS file is higher than that on the DNS server.

In this way, if you want to bind a domain name to an IP address, you can add a resolution entry to the HOSTS file.

Step 1: Use "start-> Search" to search for a file named hosts.

Step 2: Of course, readers who already know the path can directly find the HOSTS file in the c: \ windows \ system32 \ drivers \ etc directory. If your system is windows 2000, search for it in the c: \ winnt \ system32 \ drivers \ etc directory.

Step 3: double-click the HOSTS file and select to open it with the "Notepad" program.

Step 4: We will see all the content in the HOSTS file. By default, there is only one line of content "127.0.0.1 localhost ". (Other rows with # In front of them are not real content, but help information)

Step 5: add the entries you want to perform DNS resolution to the HOSTS file. The specific format is to first write the corresponding IP address of the domain name, and then use a space to connect the domain name information. For example, I have added "211.153.80.1 www.ftedu.gov.cn" and "10.82.0.1 www.ftedu.gov.cn.

Step 6: After the settings are complete, when we access www.ftedu.gov.cn, it will be automatically parsed Based on the Intranet or Internet.

Iii. Summary:

Through the four steps described above, we can solve most DNS resolution problems. The first three of these methods are step-by-step DNS resolution faults, the last modification to the HOSTS file is a matter of privilege when there is no way. Of course, no matter which method we use, we can solve the network faults caused by DNS resolution errors.

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