DNS
The Internet's directory: resolvers, root and authoritative servers, record types, TTL and caching, and what happens when DNS goes down or an address changes.
- 45 cards
- 4 topics
- Free
The outline, topic by topic
Each topic is weighted the way the exam weighs it.
- The basics
- Records
- Caching and TTL
- Failures
A few cards from the deck
DNS resolver (recursive): what is it?
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The server that looks up the answer for the client by asking the other DNS servers, then caches it
It is often the Internet provider's or a public resolver.
With nothing cached, in what order does a resolver find the address of www.exemple.fr?
- Authoritative server, then root server, then the .fr server
- The .fr server, then root server, then authoritative server
- Straight to exemple.fr's web server
- Root server, then the .fr server, then exemple.fr's authoritative server
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Root server, then the .fr server, then exemple.fr's authoritative server
Each level points to the next: the root knows .fr, .fr knows exemple.fr, which gives the answer.
Authoritative DNS server: what is it?
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The server that holds a domain's official records
This is where a domain's records are edited; resolvers only relay and cache them.
Recursive DNS resolution: after “Question to the resolver” (Client → Resolver), what is the next message?
- Referral to .fr (Root server → Resolver)
- Question to the .fr server (Resolver → .fr server)
- Question to the root (Resolver → Root server)
- Referral to exemple.fr (.fr server → Resolver)
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Question to the root (Resolver → Root server)
Address of www.exemple.fr?. With nothing cached, the resolver starts at the top of the tree.