Computer Networks · free preview

The Domain Name System

Routers want addresses and humans want names, so the Internet runs middleware that translates, a hierarchical name space where each level delegates authority to zones, administrative subtrees each served by two or more name servers holding resource records of several types, address records, name-server records for delegation, aliases, mail exchangers, each with a time-to-live that makes caching legal, and resolution walks the hierarchy from root to top-level domain to authoritative server, with local recursive resolvers doing the walking on clients' behalf and caching every answer so the root servers see a trickle of the world's curiosity.

1. Names for Humans, Addresses for Routers

Names for Humans, Addresses for Routers

2. From One File to a Hierarchy

From One File to a Hierarchy

3. Records, Types, and the License to Cache

Records, Types, and the License to Cache

4. The Walk Down the Tree

The Walk Down the Tree

5. Middleware's job

Why is a name service called middleware?

6. The unit of delegation

In the DNS hierarchy, what exactly is a zone, and what role does it play in delegation?

7. Reading a record

Which resource record type expresses delegation to a child zone?

8. The load-bearing cache

Why is caching load-bearing in DNS rather than merely an optimization?

9. Recursive versus iterative

Who does the walking when your laptop resolves a name?

10. The second lookup

Two users of the same resolver look up the same popular site in succession. Why is the second lookup fast?

11. The delegation record

Which resource record type names the authoritative server for a child zone?

12. The expiry field

Which resource record field bounds how long an answer may be cached?

13. The walking server

What kind of name server chases referrals from the root down to the authoritative server on a client's behalf?

14. The address answer

Which record type maps a host name to its IP address?

Practice this interactively

Free account · instant grading · spaced review that schedules itself.

Start this course for free