Routing: How a Path Is Learned · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

How routers learn the way together

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

  1. What does each router keep for forwarding?

    • Nothing, it guesses each time
    • A table saying where to send traffic per destination
    • The whole internet drawn on paper

  2. In the graph picture of a network, what is a path?

    • A chain of edges from start to finish
    • One router working alone
    • A cable cut in half

  3. In distance vector, routers repeat exchanges until no table changes any more.

    Circle one:   True   False

  4. A link fails. Why do some routers point the old way for a while?

    • The bad news still walks neighbor by neighbor
    • Packets enjoy long detours
    • They never stored any table

  5. Three routers stand in a line A B C. How does A learn C?

    • A phones C directly
    • C deletes itself
    • B passes its distance along, round by round

  6. Routers A B C form a line with each link cost 1. After tables settle, what is the cost from A to C?

    Answer: ______________

  7. A student says one router knows the whole network at the start. What is the error?

    • Tables are never used
    • Routers know nothing at all
    • Each router knows only seen links and heard neighbors, then shares

  8. Traffic between two organizations takes a longer road though a shorter one exists. Why?

    • Routers cannot count
    • Border policy and business shape which paths are accepted
    • Short links always break
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Answer key

For grown-ups. Fold this page away before handing over the rest.

How routers learn the way together W1-mt_gyqPDrV6Uo-s1

  1. A table saying where to send traffic per destination · Tables hold the learned next steps per destination.
  2. A chain of edges from start to finish · Paths run vertex to vertex along edges.
  3. True · Round after round of better news ends in agreement.
  4. The bad news still walks neighbor by neighbor · Failure word spreads one hop per round, so old pointers linger.
  5. B passes its distance along, round by round · Neighbors share best distances until far ends fill in.
  6. 2 · A to B is 1 and B to C is 1, so the full path costs 2.
  7. Each router knows only seen links and heard neighbors, then shares · Knowledge starts local and grows by sharing.
  8. Border policy and business shape which paths are accepted · Gate owners pick allowed paths for their own reasons.
Worksheet · LightMySky