The Domain Name System (DNS) is the phonebook of the internet. It is the service that translates human-readable website names, such as google.com into IP addresses. When you type in a website’s name in the address bar of your browser, your computer queries the DNS to get the IP address associated with it.

So why do computers need to check the DNS for websites that have already been visited? To understand this, it is important to know that the DNS records for a website can be updated from time to time.

When you attempt to reach a website, your browser must retrieve the most current DNS record. This ensures that you are always directed to the correct IP address for the desired website. If your computer did not check the DNS, then it could run into the risk of being directed to a wrong IP address or a malicious website.

Another reason why computers need to check the DNS is because websites often move to different servers. As a result, the DNS is updated to reflect the new IP address for the website. If your computer failed to update this information, then it could again end up in the wrong website.

Apart from the above two reasons, there may be other reasons why your computer needs to periodically check the DNS. For instance, your computer may need to update the DNS record when a website changes the address of its webpages. This ensures that your browser always directs you to the correct address.

In conclusion, computers must check the DNS to ensure that they are being directed to the correct IP address. Without this, they could be directed to malicious websites or incorrect webpages, making your online experience much more dangerous.