Dns is a hierarchical recursive service. When you make a DNS query, such as requesting "www.google.com", you typically do not do the full resolution in your app

Dns is a hierarchical recursive service. When you make a DNS query, such as requesting "www.google.com", you typically do not do the full resolution in your application - but you do make the DNS query on your application. What you instead do is make a DNS request to your configured "recursive" server, asking it to make further queries on your behalf if it doesn't know the answer. We do something obviously silly for this exercise - we assume that all caches are cold, because the point of a recursive DNS server is mostly to act as a cache. So we'll be going through a bunch of queries that usually are simply answered from cache instead. At the top are 13 "root dns servers". These return responses for top level domains, such as ".com". When you want to request www.google.com, first you have to ask who controls ".com". Your recursive server (just "you" from now on) sends a request to the root servers - "Who are the nameservers (ns) for .com?" Also written as "QUERY .com NS". The root servers will answer - "A(answer) .com NS 1.2.3.4 AA (Authoritative answer)". The root dns servers believe they are the authority for the "." Zone, because they are. The recursive resolver, you, then use this knowledge. You ask a similar query of the ".com" nameservers - "Q google.com NS" they respond, giving you an authoritative answer for google.com "A google.com NS nameservers.google.com AA". But you don't know who the nameservers for google.com, how do you resolve this loop? DNS has a mechanism for that. It includes a few extra records, called glue records, to close the gap. "X(tra) nameservers.google.com 8.8.9.9" Finally, you know who the nameservers for google.com are - You then send them a request. "Q www.google.com A(Internet Protocol)" you might instead send an AAAA request, for an ipv6 address, instead. There's a ton more - Support for text records of arbitrary type, support for addressing schemes that no longer see use, etc. but thems the basics. You can run your own whole Internet, if you want to - Just build your own recursive server pointing at your own roots, and then host whatever you want on whatever up you want - Just don't expect to be able to connect to the real Internet at the same time. Also basically everything phones home and breaks. :shrug: