The domain name system is a global distributed database of matching all web addresses and IP addresses. When you go to different sites, the browser converts the name to an IP address and this data is stored locally on your computer in a cache to speed up access to the same site with the same domain name. And the whole system works well most of the time, but at the same time it makes it difficult to quickly see the changes you are making in the DNS system.
For example, the site has changed the IP address to another, and you still have the old cache in the cache and therefore the site simply does not open.
To clear DNS cache on a windows computer follow there steps :
In the Apple operating system, all commands are entered in the "Terminal". The easiest way to get into it is through Spotlight: click on the search icon in the upper right corner.
sudo killall -HUP mDNSResponder; sleep 2; echo macOS DNS Cache Reset ;
sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder ;
sudo dscacheutil -flushcache;sudo killall -HUP mDNSResponder ;
dscacheutil -flushcache;sudo killall -HUP mDNSResponder ;
sudo killall -HUP mDNSResponder ;
dscacheutil -flushcache ;
lookupd -flushcache ;