Glossary

DNS

The system that translates names into IP addresses.

DNS turns example.com into an IP address. Recursive resolvers (your ISP's, or 8.8.8.8) chase the answer on your behalf and cache it for the record's TTL; authoritative servers hold the zone's truth.

Caching is why changes propagate gradually rather than instantly, and why lowering a record's TTL before a migration is standard practice. When a site is "down" but pings by IP, DNS is the first suspect — dig is how you interrogate it.

See it in practice

$ dig example.com +short && dig @8.8.8.8 example.com +short

What your resolver says, then what a public one says. Differences mean caching or a broken record.

Where you'll meet it

dig

Ask DNS questions directly: A, MX, TXT records, and which server answered.

ping

Check whether a host is reachable and measure round-trip latency.

curl

Download files, test APIs, send POST requests with JSON, and inspect headers.

Learn these concepts by typing them: the interactive course builds them up lesson by lesson in a real simulated shell.