← ACARA Digital Technologies Years 9–10

Internet Protocol (IP)

The protocol that puts source and destination IP addresses on each packet so routers can deliver it. It is best-effort: it does not guarantee a packet arrives.

Part of: ACARA Digital Technologies Years 9–10 — Networked Systems and Access Control — Module 51, WA Computer Science ATAR Year 11 — Network Communications — Module 51

Understanding Internet Protocol (IP) in ACARA Digital Technologies Years 9–10

What it does: A dropped packet shows best-effort delivery, because IP makes no promise and does not resend lost packets. IPv4 uses four numbers such as 192.168.1.20, while IPv6 uses longer hexadecimal addresses such as 2001:db8::1. IP addresses each packet with where it came from (source) and where it is going (destination). Routers read the destination address to decide where to send it next. Both versions of IP only address and route packets. Reliability must come from another protocol, such as TCP.

Common mistakes: Routers deliver a packet using its destination IP address, not its source address. The line should be forward_to(packet["dst"]). An IPv4 address is made of four numbers separated by dots, so the check should be len(parts) == 4, not 6.

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Free printable worksheet with full answer key — or add this module to a class and your students practise it interactively.

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This module's key terms are also in a printable crossword (Modules 41–55) and word search (Modules 12–55).

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Learning
Duo
What does the Internet Protocol (IP) put on each packet so routers can deliver it?
Source and destination IP addressesA password and a username
Matches
IP guarantees every packet will arrive, so no packet is ever lost
↓
IP is best-effort and gives no guarantee, so packets can be lost, and a protocol like TCP is needed to detect and fix this
Applying
Meanings
Term
Internet Protocol (IP)
Meaning
The protocol that puts source and destination IP addresses on each packet so routers can deliver it. It is best-effort: it does not guarantee a packet arrives.
Practice
packet.source <- "192.168.1.10"
Testing
Gaps
packet. = "192.168.1.20"
Check Answer
Spots
3packet["dst"] = "203.0.113.9"
4forward_to(packet["src"])

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Quick Questions

1. What does the Internet Protocol (IP) put on each packet so routers can deliver it?
A. A password and a username
B. Source and destination IP addresses ✓
IP addresses each packet with where it came from (source) and where it is going (destination). Routers read the destination address to decide where to send it next.
2. Which statement about IP is true?
A. IP is best-effort: it does not guarantee a packet arrives ✓
B. IP guarantees every packet arrives
IP only tries its best to deliver packets. A packet can be lost, delayed or arrive out of order, and IP itself does not fix this.
3. A router drops a packet because its link is overloaded. What does IP do about it?
A. Nothing. IP does not resend lost packets ✓
B. IP automatically resends the packet
IP is best-effort and does not track or resend packets. A higher-level protocol such as TCP can notice the loss and ask for the packet again.
4. Which part of the packet does a router read to decide where to forward it?
A. The destination IP address ✓
B. The source IP address only
The router matches the destination address against its routing table to pick the next hop. The source address tells the receiver who sent the packet.
5. Which of these is an IPv4 address?
A. 2001:0db8:85a3::8a2e:0370:7334
B. 192.168.0.12 ✓
IPv4 addresses use four numbers from 0 to 255 separated by dots. The other address is IPv6, which uses hexadecimal groups separated by colons.

Match the Pairs

Source IP: 192.168.1.20 → The sender's address, which IP puts on each packet so the destination knows where it came from
Destination IP: 203.0.113.8 → The receiver's address, which routers read to decide where to forward the packet
IP is best-effort: it tries to deliver each packet but does not guarantee that it arrives → Packet 7 dropped by a busy router - IP does not resend it
IP has two versions, with IPv4 using shorter addresses than IPv6 → IPv4: 192.168.1.20 IPv6: 2001:db8::1
IP guarantees every packet will arrive, so no packet is ever lost → IP is best-effort and gives no guarantee, so packets can be lost, and a protocol like TCP is needed to detect and fix this
Each packet carries only a destination IP address, with no source IP address → Each packet carries both a source and a destination IP address, so the receiver knows who sent it and can reply

Key Term

Internet Protocol (IP)
The protocol that puts source and destination IP addresses on each packet so routers can deliver it. It is best-effort: it does not guarantee a packet arrives.

Fill in the Blanks

1. packet.source = "192.168.1.20" packet.dest = "203.0.113.9"
Hint: Type the packet field name that holds the sender's IP address.
2. deliveryGuaranteed = false
Hint: Type the boolean value that shows IP does not promise a packet will arrive.
3. addressBits = 32 version = "IPv4"
Hint: Type the IP version that uses 32-bit addresses.
4. if version == "IPv6": addressBits = 128
Hint: Type the number of bits in an IPv6 address.
5. if packet.dest == myIp: accept(packet) else: forward(packet)
Hint: Type the operator that checks whether the destination address equals this device's address.

Spot the Error

Question 1
A packet = {}
B packet["src"] = "192.168.1.5"
C packet["dst"] = "203.0.113.9"
D forward_to(packet["src"])
Line D — Routers deliver a packet using its destination IP address, not its source address. The line should be forward_to(packet["dst"]).
Question 2
A version = 4
B address = "192.168.0.12"
C parts = address.split(".")
D print(len(parts) == 6)
Line D — An IPv4 address is made of four numbers separated by dots, so the check should be len(parts) == 4, not 6.
Question 3
A sent = ip_send(packet)
B guaranteed = True
C if not guaranteed:
D print("may be lost")
Line B — IP is best-effort, so it does not guarantee that a packet arrives. The line should be guaranteed = False.
Question 4
A addr = "2001.db8.0.1"
B groups = addr.split(":")
C print(len(groups))
D print("IPv6 uses colons")
Line A — IPv6 addresses are written in hexadecimal groups separated by colons, not dots. It should be addr = "2001:db8::1".
Question 5
A packet = {}
B packet["dst"] = "192.168.1.300"
C send(packet)
Line B — Each number in an IPv4 address must be from 0 to 255, so 300 is invalid. A valid destination is "192.168.1.30".

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