Understand IP addresses and differentiate between types

Network Hardware – IP Addresses (IGCSE 0478)

1. What is an IP address?

An Internet Protocol (IP) address is a numerical label that uniquely identifies a device on a network that uses the Internet Protocol. It performs two essential functions:

1. Identification – identifies the host or network interface.
2. Location addressing – enables routers to forward data packets to the correct destination.

2. MAC address – the hardware identifier

• Stands for Media Access Control address.
• Stored permanently in the Network Interface Card (NIC).
• Written as six pairs of hexadecimal digits, e.g. 00:1A:2B:3C:4D:5E (or 00-1A-2B-3C-4D-5E).
• Operates at the data‑link layer (Layer 2) to deliver frames on a local network segment.
• IP addresses operate at the network layer (Layer 3) and are mapped to a MAC address by the ARP protocol (IPv4) or NDP (IPv6).

3. Types of IP addresses

3.1 By version

3.2 By scope (public vs. private)

3.3 By assignment method

4. IPv4 address structure

An IPv4 address consists of four 8‑bit octets (0 – 255). The division between network and host portions is defined by a subnet mask (or CIDR notation).

4.1 Subnet mask and CIDR notation

• Notation /n means the first n bits are the network part.
• Corresponding decimal mask for /24 is 255.255.255.0.
• Subnet mask determines how many hosts can exist in that subnet (see the quick reference table below).

4.2 Binary‑decimal conversion example (required by the syllabus)

IPv4 address: 192.168.1.10

Decimal   : 192   168    1    10
Binary    : 11000000 10101000 00000001 00001010

To convert back, group the binary octets into sets of eight and translate each set to decimal.

4.3 Subnet mask illustration

Address      : 192.168.10.25
Subnet mask  : 255.255.255.0  (/24)

Network part : 192.168.10   (first 24 bits)
Host part    : 25           (last 8 bits)

4.4 Quick reference table

5. IPv6 address structure

• 128 bits written as eight groups of four hexadecimal digits (a “hextet”).
• Leading zeros in a group may be omitted.
• One consecutive run of zero groups can be replaced by :: (only once per address).

5.1 Example of shortening

Full form : 2001:0db8:0000:0000:0000:0000:0002:0001
Shortened : 2001:db8::2:1

5.2 IPv6 address types (syllabus‑relevant)

6. DHCP – dynamic IP‑address allocation

DHCP automates the assignment of IPv4 (and IPv6 via DHCPv6) addresses, subnet mask, default gateway and DNS servers.

6.1 DHCP handshake (four steps)

1. DHCPDISCOVER – client broadcasts a request for configuration.
2. DHCPOFFER – DHCP server replies with an available IP address and lease time.
3. DHCPREQUEST – client selects an offer and asks the server to confirm it.
4. DHCPACK – server acknowledges; the client can now use the supplied address.

When the lease expires the client may renew it (DHCPREQUEST/DHCPACK) or obtain a new address.

7. Router functions (relevant to the syllabus)

• Routing – examines the destination IP address, looks up the best‑matching entry in its routing table, and forwards the packet to the next hop.
• Routing tables can be:
  • Static – manually entered entries.
  • Dynamic – learned automatically using protocols such as RIP, OSPF or EIGRP (beyond IGCSE depth, but worth naming).
• Network Address Translation (NAT) – translates private IP addresses to a single public address (or a pool). This lets many devices share one Internet‑facing address while keeping the internal network private.
• DHCP relay (IP helper) – forwards DHCP broadcast messages from a LAN segment to a DHCP server on another network.
• IP‑address configuration – routers have at least one static IP on each interface; they may also act as a DHCP server for small networks.

8. Data transmission – packet switching and packet structure

• Packet switching – each data packet is routed independently; routers may receive packets out of order and re‑assemble them at the destination.
• Packet structure (network layer):

+-------------------+----------------------+-------------------+
| Header            | Payload (data)       | Trailer           |
+-------------------+----------------------+-------------------+
| Source IP address| User data (e.g.,     | Error‑checking    |
| Destination IP    | HTTP request)        | (CRC / checksum)  |
| Protocol field    |                      |                   |
+-------------------+----------------------+-------------------+

• Header – contains source/destination IP addresses, protocol identifier (TCP, UDP, ICMP), and other control information.
• Payload – the actual user data carried by the packet.
• Trailer – optional; often holds a checksum or CRC used for error detection.
• USB (Universal Serial Bus) – mentioned in the syllabus as a data‑transmission interface; it provides serial data transfer for peripheral devices such as keyboards, mice and storage.

9. Quick revision checklist

1. Convert an IPv4 address between binary and decimal forms.
2. State the three private IPv4 CIDR blocks and their address ranges.
3. Explain the difference between static and dynamic IP allocation, including the four DHCP handshake steps.
4. Identify a valid IPv6 address, shorten it correctly, and name at least one IPv6 address type.
5. Describe the main functions of a router: routing tables, NAT, and DHCP relay.
6. Label the three parts of a network‑layer packet (header, payload, trailer) and recall that packet switching may reorder packets.
7. Recall the format and purpose of a MAC address.
8. State the role of USB as a serial data‑transmission interface.

10. Suggested diagram (for classroom use)

A simple LAN layout showing:

• Router – one static public IP (e.g., 203.0.113.2/30) and two LAN interfaces with private IPs 192.168.1.1/24 and 192.168.2.1/24.
• DHCP server (could be the router) assigning dynamic IPv4 addresses in the range 192.168.1.100 – 192.168.1.200.
• Layer‑3 switch (optional) illustrating routing between VLANs.
• Three end devices:
  • Desktop – static IP 192.168.1.10.
  • Laptop – dynamic IP obtained via DHCP.
  • Smartphone – IPv6 address (e.g., 2001:db8::c0a8:1).
• Arrows indicating packet flow, with an inset showing:
  • Network‑layer header (source/destination IP).
  • Data‑link‑layer frame containing source/destination MAC addresses.