DNS

DNS means Domain Name System. Paul Mockapetris described it in 1983. A person remembers a name, and a computer goes by a number. That number is the IP address. The query first goes to a nearby resolver. If the resolver does not know the answer, it asks the server responsible for the name. The responsible server keeps that name's records. When a record changes, the old answer can stay in memory for a while. That is why the change does not appear everywhere in the same second.

DNS is for a site name, a mail server, and tying one name to another name. The browser does not take the page from DNS. It first takes the address, then goes by HTTP.

• Tying a name to one IP address
• Saying which server mail goes to
• Pointing one name onto another name
• Keeping an old address in memory for a while

With DNS you change where a name looks. You do not move the file. An A record says the number, a CNAME says another name, and an MX says the mail server. A wrong record can send the site to another machine. An HTTPS certificate is for the name. When the address changes, the certificate itself does not go stale, but the name must point at that machine.

Writing one record is easy. The difficulty is the waiting time. An old answer can stay for hours. Two CNAME records that look at each other make a loop, and the name does not open. Changing the name and leaving the file on the old server also loses the page.

Advantage: a person does not memorize the number, and the name can stay when the address changes. Limit: the change does not appear everywhere at once. DNS is not the content of the page. The content is on the server the address points to.

The name is the part a person reads. A record is one answer for that name. The resolver is the nearby server that asks.

• An A record says the number
• An AAAA record says the newer kind of number
• MX directs mail
• The waiting time is the life of an old answer

This is a simple line that asks for a name's number. It does not move the site and it does not change the record.

nibrascode.com.  A  203.0.113.10

• Are DNS and HTTP the same? No. DNS turns a name into a number. HTTP asks the server at that number for the page.
• When you change a record, does the site open everywhere at once? Not always. An old answer can stay for a while.
• Does DNS move the file? No. It only says where the name looks.