IP Addressing and How Routers Choose a Path · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Finding the way for every packet

Computing · Computer Systems · ages 17-18
Name ______________________   Date ____________

  1. Your address is 210.1.1.100 with mask 255.255.255.224. Which address labels the whole subnet?

    • 210.1.1.100
    • 210.1.1.127
    • 210.1.1.96

  2. A subnet mask splits an IPv4 address into which two parts?

    • The sender part and the message part
    • The network part and the host part
    • The username part and the password part

  3. A subnet mask marks which part of an address names the network.

    Circle one:   True   False

  4. A packet is headed outside its own network. Where does the device send it?

    • Back to itself for safekeeping
    • To the default gateway
    • To any address it likes

  5. A router sends 192.168.1.0/24 out on link A, 192.168.0.0/16 out on link B, and everything else out on link C. A packet for 192.168.1.20 arrives. Which link does it leave on?

    • Link A
    • Link B
    • Link C

  6. Two packets of one message always travel the same route.

    Circle one:   True   False

  7. Why does no router need a map of the whole internet?

    • Each router only picks the next hop
    • Packets carry a full map with them
    • Routers never forward faraway packets

  8. A router sends 192.168.1.0/24 out on link A, 192.168.0.0/16 out on link B, and everything else out on link C. A packet for 192.168.2.5 arrives. Which link does it leave on?

    • Link C
    • Link A
    • Link B
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Answer key

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

Finding the way for every packet W1-mt_l0dRGocXGw-s1

  1. 210.1.1.96 · The lowest address of the subnet is the network address, 210.1.1.96.
  2. The network part and the host part · The mask marks which bits name the network and which name the device.
  3. True · That marking job is exactly what the mask is for.
  4. To the default gateway · The default gateway is the usual door for packets leaving the network.
  5. Link A · It matches the /24 and /16 rows, and the longer /24 wins.
  6. False · Routers judge each packet afresh, so later packets may go another way.
  7. Each router only picks the next hop · Choosing the next hop well at every step gets each packet home.
  8. Link B · Only the /16 row matches, so link B takes it.
Worksheet · LightMySky