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Worksheet

F10.5 Addresses and packets

Networks · GCSE · OCR J277 1.3.2, AQA 8525 3.5, Edexcel 1CP2 4.1.3 · about 15 min

BugBotLab
NameClassDate

What this lesson is about

MAC and IP addresses, IPv4 and IPv6, and packet switching.

Questions 6 marks in all

  1. [1 mark]Which of these is a valid IPv4 address?

    1. A192.168.0.12
    2. B192.168.300.1
    3. C3C:61:05:1A:9F:02
    4. D10.0.1

  2. [1 mark]What is a MAC address used for?

    1. AIdentifying a network interface, to deliver data within a local network
    2. BRouting data between networks
    3. CNaming a website
    4. DEncrypting data

  3. [1 mark]How many bits is an IPv6 address?

  4. [1 mark]Why do packets have sequence numbers?

    1. ASo they can be put back in order when they arrive
    2. BSo routers know the route
    3. CTo encrypt them
    4. DTo make them smaller

  5. [1 mark]Which is in a packet header?

    1. AThe destination IP address
    2. BThe whole file
    3. CThe user's password
    4. DThe web page's title

  6. [1 mark]What does this program print?

    packets = ["2/2:Bot", "1/2:Bug"]
packets.sort()
print("".join(p[4:] for p in packets))

The task: packets

Write make_packets(message, size), which splits message into pieces of size characters and returns them as packets in the form <number>/<total>:<piece>. Make the packets for message with a size of 10, print each one, and send each by radio. The packets arrive in the order [packets[2], packets[0], packets[1]]: sort them back into order by their sequence numbers, and print reassembled: <message> and matches: True (or False).

# the two lines every program starts with: the commands, then the robot
from bugbot import *
connect()

message = "robot 7 at 25,40 battery 87%"

Plan your program here, then type it in and press Run.

QR code
Do it on the robot
www.bugbotlab.com/learn/f10-5-addresses-and-packets/
The simulator checks it and tells you when it passes. Nothing to install, no account.

Challenges

  1. Shuffle the packets with random.shuffle and check they still reassemble.
  2. Add a checksum to each packet: the total of the ord() values of its characters, modulo 100. Check it on arrival.
  3. How many IPv4 addresses are there exactly? How many IPv6? Use 2 32 and 2 128.