Use Shenzhen Telecom DNS with caution

Original link: https://www.williamlong.info/archives/6842.html

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When using Shenzhen Telecom’s broadband dial-up Internet access, if you do not manually set the DNS, the system default DNS will be used after dialing up: Shenzhen Telecom’s DNS, there are many problems with this DNS, it is recommended that telecom users use a more professional and effective domestic public DNS. For example, Ali DNS, Tencent DNS, etc.

When I was surfing the Internet recently, I found that many frequently visited webpages would have problems, such as the pictures could not be displayed, Javascript could not run, etc. After a lot of investigation, I found that the root of the problem was that I used an unreliable DNS: Shenzhen Telecom DNS (IP address 202.96.134.133).

The specific situation is as follows. When I used Google Translate to translate Chinese and English, I found that some pictures of the website could not be displayed. Press F12 to open the Google Chrome console, and found that the resources under the fonts.gstatic.com domain name could not be accessed. In addition, I visited other websites and found that Javascript could not be run. Press F12 to open the Google Chrome console, and found that the domain name cdnjs.cloudflare.com where jQuery is located cannot be accessed.

I pinged these two domain names and found that the IP addresses were wrong, and they were both changed to 127.0.0.1. In order to confirm whether it was a DNS problem, I used the nslookup command to verify.

The nslookup command is used to query DNS records to check whether the domain name resolution is normal, and to diagnose network problems when the network fails. The command format is: nslookup domain [dns-server]

I enter the following command

nslookup fonts.gstatic.com 202.96.134.133

nslookup cdnjs.cloudflare.com 202.96.134.133

nslookup

The IP addresses returned by the system are ::1 and 127.0.0.1. ::1 is the IPv6 address, which is equivalent to 127.0.0.1 in IPv4.

For comparison, I use commonly used domestic public DNS, such as Ali DNS, Tencent DNS, Baidu DNS, 114DNS, etc. for verification, all of which can return the correct IP address, as shown in the figure below.

nslookup

So I came to the conclusion that Shenzhen Telecom was messing around.

I have only found that the domain name resolution of two regular websites has been illegally tampered with. I believe that the number of domain names that have been illegally tampered with should be very large. Given that Shenzhen Telecom’s DNS is so unprofessional and unreliable, it is recommended that telecom users in Shenzhen go online. Manually set the DNS to more professional and reliable other domestic DNS, such as Ali, Tencent and other DNS, don’t use Shenzhen Telecom’s DNS, so as not to bring a lot of unnecessary problems to your Internet.

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