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→Registering a domain name
* You can add whatever DNS records you want for your domain, and you also control all the subdomains of that domain. You won't need to pay extra for one.two.three.four.somedomain.com
* After you add you records - they will be available to the world almost immediately. Except: see next section.
If you're a more advanced user: you can configure your domain records to be stored on and served by your own DNS server(s). You won't be doing that in this course. It's a lot of hard work and requires a cooparative registrar to set up glue records for you.
=== Caching ===
Because DNS is used so much (see a typical webpage): there are countless DNS queries done everywhere all the time.
The responses to those queries are cached (stored closer to the questioner) in order to minimize load on the authoritative servers. They are cached for a specific amount of time - typically controlled by the domain owner, though cheaper registries have minimum limits.
That means that if you have an A record linking somedomain.com to 1.2.3.4, and someone does a DNS query for somedomain.com: their next query for somedomain.com will not make it to your DNS server until after the TTL expires.
That means if you change your A record to link somedomain to 2.3.4.5 instead: it may take as long as 48 hours for everyone in the world to be guaranteed to get the new record. You can see the TTL (in seconds) for a record when you use dig to do a query:
[[File:littlesvrTTL.png|border|center]]
There are websites available that can help you figure out whether your records are up to date around the world, for example https://www.whatsmydns.net/
== Private DNS ==
If you only need DNS records inside your organization (e.g. on an LAN/intranet): you can avoid paying a registrar for each domain.
You do that by running a DNS server on your LAN, and making sure all the machines on that network are configured to use your internal DNS server. Curiously: in such a setup the administrator can have control over all DNS records including for domains owned by someone else:
[[File:DNSquery.png|800px|border|center]]
* you should have received an email about a Bindistrar account that's been created for you
* set up an A record for yourmysenecaid.ops345.ca to point to your elastic IP (the one assigned to router)