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DNS and domains flashcards

Buy a domain, point it at a site, set up email that lands in inboxes, move hosts without downtime and keep the name safe.

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Beginner friendly, starts from zero
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DNS and domainsStart from zero · 1 of 11

What is a ?

A is an easy name like example.com that people type to reach a website or send email. Behind it, computers use number addresses that are hard to remember.

Names for people, numbers for machines.
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What you will learn

  1. Start from zero

    • What a domain is6 cards
    • Key words5 cards

  2. Core basics

    • Buying and nameservers3 cards
    • Core records5 cards
    • TTL and caching2 cards
    • Lookups and connecting a site4 cards
    • Email basics2 cards

  3. Next steps

    • How lookups flow4 cards
    • Apex and www2 cards
    • Email done right3 cards
    • Certificates and DNS3 cards
    • Migrations2 cards
    • Transfers, expiry and other records3 cards

  4. Go deeper

    • DNSSEC and encrypted DNS3 cards
    • Takeovers, hijacks and modern records4 cards
    • Internal DNS2 cards
    • DNS at scale3 cards
    • Operations and privacy4 cards

Final test and certificate

10 questions drawn fresh from the whole topic, about 15 minutes. Sign in, score 80% or more and get a free certificate with your name and a public check link anyone can open, such as an employer or a teacher. Not signed in? Try a practice test from the cards.

Take the final test

About these cards

  • Reviewed 26 October 2026
  • CoversDNS (RFC 1034/1035 and updates)DMARC (RFC 7489)CA/B Forum rules as of 2026
How these cards are made

DNS and domains at a glance

A domain is your name on the internet, and DNS is the system that tells every computer where that name lives.

A domain is like a shop name, and DNS is the directory at the mall entrance. People remember the name; the directory tells them which unit to walk to, and you can move units by updating the directory.

Words you will meet

Domain name
A name like example.com that people type instead of a number
TLD
The last part of a domain, like .com, .in or .dev
Registrar
The company you buy and renew a domain from
DNS
The system that turns names into IP addresses and other facts
Record
One line in DNS, like "this name points to this address"
Nameserver
The server that holds a domain's records and answers questions about them
TTL
How many seconds others may remember an answer before asking again
Subdomain
A name under your domain, like shop.example.com

The steps

  1. 1. Start from zero (11 cards): What a domain is, how DNS is like a directory, and the words used for buying and pointing names.
  2. 2. Core basics (16 cards): Buying and renewing, nameservers, A, AAAA, CNAME, MX and TXT records, TTL, subdomains and your first dig commands.
  3. 3. Next steps (17 cards): How lookups really flow, apex and www, email with SPF, DKIM and DMARC, CAA, migrations, transfers and certificates.
  4. 4. Go deeper (16 cards): DNSSEC, encrypted DNS, HTTPS records, takeovers and hijacks, split-horizon, anycast and DNS at scale.
All 11 cards in Start from zero
What is a domain name?
A domain name is an easy name like example.com that people type to reach a website or send email. Behind it, computers use number addresses that are hard to remember.
What are the parts of shop.example.co.in?
Read right to left: .in is the country TLD, co.in is a second-level zone under it, example is the name you registered, and shop is a subdomain you created yourself.
What is DNS, in everyday words?
DNS is the internet's directory. When you type a name, your device asks DNS "where is this?" and gets back an address to connect to, usually in a few milliseconds.
Do you own a domain forever when you buy it?
No. You rent it for one to ten years at a time and must renew. If you forget, it expires and someone else can register it after a short grace period.
Registrar, registry and DNS host: who does what?
The registry runs a whole TLD, like .com. The registrar sells you a name in it. The DNS host stores your records. One company can do all three jobs for you, or you can split them.
What is a DNS record?
One line of facts about a name, such as "example.com points to 203.0.113.10" or "email for example.com goes to this mail server".
What is a nameserver?
The server that holds your domain's records and answers questions about them. At the registrar you choose which nameservers are in charge of your domain.
What is TTL?
Time to live: how many seconds other computers may remember an answer before asking again. A TTL of 3600 means changes can take up to an hour to be seen everywhere.
What is a subdomain?
A name under your domain, like shop.example.com or mail.example.com. You create as many as you like for free in your DNS records.
Which TLD should a new project pick?
.com is the most familiar worldwide. A country TLD like .in signals a local business. Newer ones like .dev or .app work well for tech, and force HTTPS in browsers.
What do you need before starting, and what can you do after?
Just a card to buy a domain, or a free subdomain to practise on. After this topic you can buy, point, protect and move domains, and make email from them reach inboxes.
DNS and domains cheatsheet

Record types

  • A / AAAA Name to IPv4 / IPv6
  • CNAME Name is an alias of another name
  • MX 10 mail.host. Where email goes, lower first
  • TXT Proofs, SPF, DKIM, DMARC
  • NS Which nameservers run the zone
  • CAA 0 issue "ca.example" Allowed certificate issuers
  • HTTPS / SVCB Protocol and address hints

dig

  • dig NAME A +short Just the answer
  • dig NAME MX Mail servers with TTL
  • dig @ns1.host NAME Ask the source directly
  • dig +trace NAME Follow from the root
  • dig -x 203.0.113.10 Reverse lookup
  • dig NAME +dnssec Show signatures

Email records

  • v=spf1 include:HOST ~all Allowed senders
  • SELECTOR._domainkey DKIM public key location
  • _dmarc v=DMARC1; p=none; rua=mailto:... Start DMARC with reports
  • p=quarantine / p=reject Spam folder / refuse fakes
  • MX 0 . Domain accepts no mail

Moves and safety

  • TTL 300 a day before Fast switch later
  • curl --resolve HOST:443:IP Test new server before DNS
  • Registrar lock + 2FA Stop hijacks
  • Auto-renew on Never lose the name
  • Delete record before resource No dangling CNAMEs
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