How can I tell if DNS is faulty? Teach you to quickly locate the root cause of the problem

in daily network use, we often encounter the situation that the website cannot be opened and the page load times out but can chat normally, which is likely to be a failure of DNS. DNS, as the "translator" of the network, is responsible for converting the domain name into the Internet Protocol Address that the server can recognize. Once it has a problem, network access will be confused. This article will explain how to judge DNS failures from multiple dimensions, teach you to quickly locate the root cause of the problem through simple operations, bid farewell to network cards and inaccessible troubles, and easily restore a smooth network experience.

, from the basic network phenomenon to judge DNS failure?

many DNS failures will be manifested through intuitive network phenomena, we can start with these common phenomena to preliminarily determine whether there is a problem with DNS.

1, the domain name cannot be accessed but the IP can be connected normally

when you enter the domain name of a commonly used website, the page always shows that it cannot be accessed, but the page can be opened normally through the public Internet Protocol Address of the website, which is the most typical phenomenon to judge DNS failure. Because the direct use of IP access skips the domain name resolution of DNS, indicating that there is no problem with the network connection itself. The problem lies in the conversion process of domain name to IP.

2, some sites access abnormal other sites normal

if only a few specific websites cannot be opened, most other websites can be accessed normally, which may also be caused by DNS failure. This is usually because the local DNS server does not cache the resolution records of these specific domain names, or the resolution records are wrong and cannot complete the normal domain name conversion.

Second, with the help of system built-in tools to determine DNS failure?

In addition to intuitive network phenomena, we can also use the network tools that come with Windows, Mac and other systems to conduct more accurate detection and further judge DNS failures.

1, use the ping command to help determine the DNS fault

enter ping plus the target domain name in the command prompt or end point of the system, such as ping www.baidu.com, if the prompt "cannot resolve the domain name" is returned, it means that the DNS cannot complete the resolution work; if the corresponding Internet Protocol Address can be returned and the delay is normal, it means that the DNS resolution function is normal. It should be noted that some servers have disabled the ping function. At this time, even if the DNS is normal, it will return a timeout, which needs to be verified in combination with other tools.

2, through the nslookup command depth judgment DNS fault

nslookup is a tool dedicated to DNS detection. Enter nslookup plus the target domain name in the command line, and it will directly display the address of the DNS server and the resolved Internet Protocol Address. If the "server failed" or "domain name not found" prompt is returned, it means that the DNS server itself cannot respond normally, or does not have resolution rights for the domain name; if it can return the Internet Protocol Address normally, it means that the DNS resolution process is normal.

three, through the multi-scene comparison to determine the DNS fault?

the detection of a single scene may be accidental, through the comparison test of multiple scenes, the scope and root cause of DNS faults can be more accurately judged.

1, replace the network environment to judge the DNS fault

If you are currently using the WiFi at home, you can switch to a mobile phone hotspot or other WiFi network and try to access the website that cannot be opened before. If you can access it normally in the new network environment, it means that there is a problem with the DNS server in the original network environment; if you still cannot access it, it may be a problem with the domain name itself, or an abnormality in the global DNS resolution.

2, replacement equipment test to judge DNS fault

use other devices under the same network, such as another computer, mobile phone or tablet, to access the same website. If other devices can access normally, it means that there is an error in the DNS setting of the current device, such as manually setting an invalid DNS address; if all devices cannot access, it is most likely that the DNS server of the router or network service provider has failed.

4. Determine the root cause of DNS failure from advanced details?

when the DNS fault is initially judged by the above method, it can also start from some advanced details to accurately locate the specific root cause of the fault.

1, view the DNS cache to determine the DNS fault

system will automatically cache the domain name records that have been resolved. When the cache records expire or there is an error, it will also cause DNS failure. In Windows systems, you can clear the DNS cache with the ipconfig /flushdns command, and in Mac systems, you can refresh the cache with the sudo killall -HUP mDNSResponder command. If you can access the website normally after clearing the cache, it means that the previous failure was caused by the wrong cache record.

2, check the DNS server status to determine the DNS fault

can check the response time, availability and other indicators of the DNS server currently in use through professional network monitoring tools. If the response time of the DNS server is too long, or the situation of frequent failure to respond, it means that the DNS server is overloaded or faulty. At this time, replace it with a public DNS server, such as 114.114.114.114 or 8.8.8.8, usually can solve the problem.

To sum up, judging DNS faults requires gradual investigation from four levels: basic phenomena, system tools, multi-scene comparison, and advanced details. First, through the initial judgment of intuitive network phenomena, and then with the help of system tools to accurately detect, then use multi-scene comparison to narrow the fault range, and finally start from the details to locate the root cause. Mastering these methods can quickly determine whether DNS is faulty when encountering network problems, efficiently solve network access problems, and ensure smooth daily network use.