Naming: DNS and the Resolution Path · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
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How a name becomes an address

Computing · Networks & Security · ages 19-20
Name ______________________   Date ____________

  1. With no usable cached delegation, where can an iterative DNS lookup begin?

    • The old server named in a previous answer
    • A root server, which gives the first referral
    • The browser's screen before any network query

  2. What can DNS resolution return for a human-readable name?

    • An address or other record associated with the name
    • A password that grants access to an administrator
    • A folder containing all page files for the site

  3. What does a DNS TTL tell a caching resolver?

    • The length of the domain name
    • The speed at which packets cross the network
    • How long a cached record may be reused

  4. A cached record has a one-hour TTL. When may the resolver need to ask for it again?

    • After one second, whether or not the answer is needed
    • After an hour has passed, when a lookup next needs that record
    • Never, because cached records remain valid for every later lookup

  5. After a .com server refers the resolver to example's authoritative servers, what happens next?

    • The resolver asks an authoritative server for the record
    • The resolver goes back to the browser without asking
    • The root server replaces the delegation with an address

  6. Right after an address change, every user sees the new server at once.

    Circle one:   True   False

  7. Caching can make repeated name lookups faster by avoiding a full hierarchy walk.

    Circle one:   True   False

  8. A site moved servers, but you still reach the old server hours later. What best explains this?

    • The screen is showing an old copy of the page layout
    • The root server deleted the new address
    • A cached DNS answer still has time left before expiry
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Answer key

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How a name becomes an address W1-mt_omttmGkEgW-s1

  1. A root server, which gives the first referral · An uncached iterative walk starts with a root server and follows referrals downward.
  2. An address or other record associated with the name · DNS stores records that associate names with values such as IP addresses.
  3. How long a cached record may be reused · TTL limits the time a caching resolver may retain a record for reuse.
  4. After an hour has passed, when a lookup next needs that record · After the one-hour retention period, a later lookup needs a fresh answer from an appropriate source.
  5. The resolver asks an authoritative server for the record · The resolver follows the referral and asks an authoritative server for the requested record.
  6. False · Some caching resolvers may still hold the old record while its TTL has time left.
  7. True · A usable cached record lets the resolver answer without repeating every referral, so the answer comes back faster.
  8. A cached DNS answer still has time left before expiry · The resolver or another cache can still reuse the old DNS answer until its TTL expires.
Worksheet · LightMySky