📖 Deeper dive reading: MDN What is a Domain Name
In the instruction about the internet we showed how an IP address can be referenced by a domain name. You can get the IP address for any domain using the dig console utility. Notice that in the following example there are actually multiple IP addresses associated with the domain name amazon.com. This allows for redundancy in case one of the IP addresses fails to successfully resolve to a valid connection because the server listening at that IP address is not responding.
➜ dig amazon.com
amazon.com. 126 IN A 205.251.242.103
amazon.com. 126 IN A 52.94.236.248
amazon.com. 126 IN A 54.239.28.85A domain name is simply a text string that follows a specific naming convention and is listed in a special database called the domain name registry.
Domain names are broken up into a root domain, with one or more possible subdomain prefixes. The root domain is represented by a secondary level domain and a top level domain. The top level domain (TLD) represent things like com, edu, or click. So a root domain would look something like byu.edu, google.com, or cs260.click. The possible list of TLDs is controlled by ICANN, one of the governing boards of the internet.
The owner of a root domain can create any number of subdomains off the root domain. Each subdomain may resolve to a different IP address. So the owner of cs260.click can have subdomains for travel (travel.cs260.click), finance (finance.cs260.click), or a blog (blog.cs260.click).
You can get information about a domain name from the domain name registry using the whois console utility.
➜ whois byu.edu
Domain Name: BYU.EDU
Registrant:
Brigham Young University
3009 ITB
2027 ITB
Provo, UT 84602
USA
Administrative Contact:
Mark Longhurst
Brigham Young University
Office of Information Technology
1208 ITB
Provo, UT 84602
USA
+1.8014220488
markl@byu.edu
Technical Contact:
Brent Goodman
Brigham Young University
Office of Information Technology
1203J ITB
Provo, UT 84602
USA
+1.8014227782
dnsmaster@byu.edu
Domain record activated: 19-Jan-1987
Domain record last updated: 11-Jul-2022
Domain expires: 31-Jul-2025This provides information such as a technical contact to talk to if there is a problem with the domain, and an administrative contact to talk to if you want to buy the domain. Maybe we should talk to Mark and see if he is willing to sell.
Once a domain name is in the registry it can be listed with a domain name system (DNS) server and associated with an IP address. Of course you must also lease the IP address before you can use it to uniquely identify a device on the internet, but that is a topic for another time. Every DNS server in the world references a few special DNS servers that are considered the authoritative name servers for associating a domain name with an IP address.
The DNS database records that facilitate the mapping of domain names to IP addresses come in several flavors. The main ones we are concerned with are the address (A) and the canonical name (CNAME) records. An A record is a straight mapping from a domain name to IP address. A CNAME record maps one domain name to another domain name. This acts as a domain name alias. You would use a CNAME to do things like map byu.com to the same IP address as byu.edu so that either one could be used.
When you enter a domain name into a browser, the browser first checks to see if it has the name already in its cache of names. If it does not, it contacts a DNS server and gets the IP address. The DNS server also keeps a cache of names. If the domain name is not in the cache, it will request the name from an authoritative name server. If the authority does not know the name then you get an unknown domain name error. If the process does resolve, then the browser makes the HTTP connection to the associated IP address.
As you can see, there is a lot of levels of name caching. This is done for performance reasons, but it also can be frustrating when you are trying to update the information associated with your domain name. This is where the time to live (TTL) setting for a domain record comes into play. You can set this to be something short like 5 minutes or as long as several days. The different caching layers should then honor the TTL and clear their cache after the requested period has passed.
You can pay to lease an unused domain name for a specific period of time. Before the lease expires, you have the right to extend the lease for an additional amount of time. The cost to buy the domain varies from something like $3 to $200 a year. Buying, or sub-leasing, an existing domain name from a private party can be very expensive, and so you are better off buying something obscure like idigfor.gold (currently available for only $101). This is one reason why companies have such strange names these days.
Refer to the instruction on using Route 53 if you are interested in leasing a domain name.