External DNS systems are systems that allow communication between devices over an external network such as the internet. External DNS systems resolve domain names to their IP address locations, where resources/files and other information are stored on these devices. This allows information to be sent and retrieved from devices by typing in a domain name, rather than having to remember the IP address, as names are easier to remember than long numbers. This is the main reason why a DNS system was created. For example, http://www.host.com will resolve to an IP address that locates the device you wish to communicate with. The external IP address that host.com points to, will have all the files stored on that device so that the website can load all the information you will see within a web browser. If host.com has their server configured so that you can view their website using its IP address, you can also view host.com by typing the IP address that has been resolved from the domain name into your web browser. I have extensive knowledge in DNS management as I used to spoof the resolved IP addresses from domain names allowing me to use my own resources/files that was requested from servers. My references are my personal knowledge. I’m going extend this more to give more information as to how DNS management works from on internet Service Provider (ISP) level or an external DNS management system such as Googles. Almost all internet service providers and management systems use databases to store DNS information. This information has a Time to Live (TTL) value that is used to refresh the information stored within their database. This information is usually cached for the length of the TTL expiration time and the length of time they cache this information for varies between providers. An average length would usually be around 5 hours. So your ISP will have the domain name and the IP address that the domain name resolves to stored inside a database. If you was to change the IP address that your domain names resolved to, then you wouldn’t see this change until the TTL has expired. Resulting in you seeing and communicating with the old IP address the domain name was associated with. So for web developers, it can be frustrating, as any changes made to files, would not be visible on the internet until everyone’s ISP provider or DNS management server has refreshed the cached information based on the TTL expiration. That’s how DNS works in fine detail.