Networks and the Internet: Question 3

Worked solution

Part (a): IPv4 vs IPv6 structure

An IPv4 address is 32 bits long. It is normally written in dotted decimal notation: four decimal numbers, each from 0 to 255, separated by dots, for example 192.168.1.1.

An IPv6 address is 128 bits long. It is normally written as eight groups of four hexadecimal digits, separated by colons, for example 2001:0db8:0000:0000:0000:ff00:0042:8329.

So the key structural differences are the bit length (32 bits vs 128 bits) and the notation used to write the address (decimal, dot-separated vs hexadecimal, colon-separated). IPv6 was introduced because the pool of possible IPv4 addresses is far too small to give a unique address to every device that now needs one. [2 marks] for any one correctly stated structural difference, clearly tied to both address types.

Part (b): Public vs private IP addresses

A public IP address is globally unique across the entire internet. No two devices reachable from the internet can have the same one at the same time, and it can be contacted directly by any other device on the internet.

A private IP address is only guaranteed to be unique within its own local network. Private addresses (such as the 192.168.1.x range used here) are never forwarded across the public internet by routers, so a device carrying one cannot be reached directly from outside its own LAN.

Because private addresses never leave their own local network, the same private address can safely be reused, at the same time, on many completely separate home networks. The laptop’s 192.168.1.15 (say) does not clash with a different laptop’s 192.168.1.15 on a neighbour’s network, because neither address is ever visible outside its own LAN. It is only the router’s public IP address that has to be globally unique, since that is the one address other devices on the internet actually use to reach the household at all.

[3 marks]: [1] for correctly defining “public” (globally unique/reachable), [1] for correctly defining “private” (only unique within its own LAN), [1] for explaining that private addresses can be reused across different LANs precisely because they are never routed on the public internet.

Part (c): MAC address vs IP address

Way 1. How the address is assigned and whether it changes. The MAC address 3C-5A-B4-9E-21-07 is a physical (hardware) address, permanently built into the laptop’s NIC by its manufacturer. It does not change, even if the laptop is moved to a completely different network. The laptop’s IP address, in contrast, is a logical address assigned by whichever network the laptop is currently connected to (here, by the router). It can change over time, and it will almost certainly be different if the laptop connects to a different network altogether.

Way 2. What the address is used for. The MAC address only has meaning on the laptop’s own local network: it identifies the device to other hardware on that same LAN (for example, a switch uses it to deliver data to the correct port), but a MAC address is never used to route data across the wider internet. The IP address identifies both which network a device is on and where it sits within that network, which is exactly the information a router needs to forward data to the laptop from anywhere on the internet.

[4 marks]: [2] for way 1 (fixed/physical vs changeable/logical, correctly contrasted), [2] for way 2 (local-only delivery vs internet-wide routing, correctly contrasted). Any other correctly explained, genuine difference between the two address types is also acceptable.

Final answers

• (a) IPv4 is 32 bits (dotted decimal); IPv6 is 128 bits (grouped hexadecimal).
• (b) Public IP addresses are globally unique and directly reachable from the internet; private IP addresses are only unique within their own LAN, so the same private address can be reused on different, unrelated networks.
• (c) The MAC address is a fixed, manufacturer-assigned physical address used only for local delivery; the IP address is a logical, reassignable address used to route data across the internet.