URLs, Domains and DNS

The Essentials

This section summarises the content on this page (read on for the full tutorial):

We now know the Internet is constructed from many IP networks each containing many hosts and each host having its own dotted decimal IP address. Our router finds the best path between hosts in different IP networks. What then is a domain and how does it fit into this picture?


A Uniform Resource Locator (URL) can be pasted into your web browser and will provide the browser with sufficient information to display a unique page that is hosted at some computer somewhere in the internet. You are currently reading the page at: https://snys.nl/?page=en/tutor/tc_dns.html, you can enter this line at any internet connected computer and will always arrive at this page.


A domain is a fixed character string, known as the top level domain (TLD) name, such as .COM, .ORG, .CO.UK, .NL or .FR prefixed by any sequence of characters registered to an organisation or an individual that can then be used to obtain the IP address of one or more related host computer systems e.g. SNYS.NL. We identify the precise host we are interested in using yet another prefix e.g. WWW (the web server for that domain) but also possible are HOST1, TESTX etc.

Note that xxx@microsoft.com is not the same as xxx@micro-soft.com (dashes are not separators, this is a different domain) but xxx@accounts.microsoft.com does come from microsoft. Before opening emails and when looking at web search results always double check the domain name being used matches what you expect, again something like info@accounts_microsoft.com (good or bad?).

Of course you can still type in the IP address if you really want to. A web browser will accept as a valid request.

Domain Name Servers

Dynamic Domain Name Server - DDNS

A DDNS provides a client interface which allows the IP address associated with a particular domain name to be dynamically updated. Anyone can open an account with a DDNS supplier, some are free but in any case subscription charges for paid services are low. Opening an account allocates a user id and password, you can then add domain names as a prefix to the DDNS domain's name. e.g. myclub.selfip.com. The client code is usually in your router but may be in the IP camera a NAS box etc. Router configuration sets the domain name, the user id and password associated with your account at the DDNS. Whenever the router receives a new IP address from your ISP, it will automatically update the DDNS account with the new IP address. As a result, when away from home you can use myclub.selfip.com to access your router and thereby your local LAN's resources.



LAN protocols, MAC addresses
TCPIP Networking
IP Networks