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→DNS
Therefore DNS is a critical part of the internet infrastructure, and just about everyone who has a website needs to do something with it. Some all-inclusive web hosts offer domain name registration and automatically connect their hosting service to the domain registration, but that comes at the cost of any flexibility. From a technical point of view your domain name registration has nothing to do with the server that your DNS records are pointing to.
== DNS records ==
DNS servers store records of different types. Here are the ones you'll see most often:
* A records (the most common ones) map fully-qualified donain names (FQDNs) to IP addresses.
* CNAME records (also called aliases) map a name to another name.
* MX records store the FQDN of the mail server for that domain.
* TXT records can store almost anything and are often used for various security features.
You can use several command-line tools to query DNS servers. Some are more useful than others. Try the following:
# <source>ping littlesvr.ca</source>Notice that ICMP (ping) packets are sent to an IP address, not the FQDN. That means the ping command had to first do a DNS query (for the A record for littlesvr.ca) and therefore this is a simple way to do a DNS query, which is useful if you don't have any better tools. Notice also that this works even if the server won't respond to pings, or even if it's offline.
# <source>host littlesvr.ca
host -a littlesvr.ca</source>This is a much more DNS-specific command and has parameters that will let you ask for different record types.
# <source>dig littlesvr.ca
dig littlesvr.ca MX
dig littlesvr.ca @8.8.8.8</source>This is the one we'll use mostly in this course. The output is the most difficult to read, but the details it provides are useful when troubleshooting your DNS setup. The first dig command above asks for the A record (the default). The second asks for the MX record for littlesvr.ca. The third asks for the A record from a specific DNS server (8.8.8.8).
# Do your best to construct DNS queries using '''dig''' to get all the records set up for littlesvr.ca. Following is a screenshot of the registrar's interface:
[[File:littlesvrNamespro.png|800px|border|center]]
If you can't obtain all these records using dig: you either don't understand how DNS works or you need more practice with dig. Keep trying until you figure it out.
* typical registrar process
** caching time: https://www.whatsmydns.net/