[3.4.1–4] NIC, MAC, IP, routers

Network hardware essentials: NIC, MAC addresses, IP addressing and routers

Why this matters

Every time you send a message, stream a video or submit coursework online, your device cooperates with several pieces of network hardware and uses two kinds of addressing to move data to the correct destination. At IGCSE level you should understand what a Network Interface Card (NIC) does, what a MAC address is and how it differs from an IP address, and what a router does on a network. This page explains these ideas clearly and shows how they work together in real situations at home, at school and on mobile connections.

The Network Interface Card (NIC)

Definition and purpose

A NIC is the hardware inside a device that connects it to a network. It prepares data to be transmitted, receives incoming data and implements the rules of the data link layer on a local network. NICs exist for different media such as Ethernet (wired using twisted-pair cable and an RJ-45 socket) and Wi-Fi (wireless radio). Modern devices often include both a wired NIC and a wireless NIC.

Each NIC has a built-in unique identifier called a MAC address. The NIC handles frames on the local network segment, using MAC addresses to decide which frames to accept and which to ignore. Drivers and the operating system work with the NIC to send and receive data efficiently.

NIC capabilities

  • Framing: wrapping data with headers/trailers used by the local network technology.
  • Error detection: checking that frames have not been corrupted in transit (e.g. using checksums).
  • Speed/duplex negotiation: choosing link speed (e.g. 100 Mbps, 1 Gbps) and full/half duplex for Ethernet.
  • Wireless functions: scanning for SSIDs, handling encryption such as WPA2/WPA3 and managing radio channels.
  • MAC addressing: storing and using the device’s MAC address for local delivery.

Comparing NIC types

Different connection methods lead to different behaviours. Use the tabs to compare common NIC situations.

When used: Desktop PCs, school lab machines and consoles where a cable is practical.

Strengths: Lower latency, high and steady throughput, less interference and better security (you must plug in physically). Ideal for exams or high-stakes online tasks.

Limitations: Requires cabling and a free port on a switch/router; not convenient for mobile use.

When used: Phones, tablets and portable laptops.

Strengths: Mobility and ease of connection to different hotspots. Supports encryption and authentication.

Limitations: Susceptible to interference, distance and obstacles; speeds vary with signal quality and congestion.

Scenario: A laptop simultaneously has an Ethernet cable plugged in and a Wi-Fi connection saved.

Behaviour: The operating system chooses one interface as the active route (often wired) for internet traffic. The other interface may remain connected for local resources or be disabled automatically to avoid conflicts.

MAC addresses: identity on the local network

What is a MAC address?

A MAC address (Media Access Control address) is a 48-bit identifier assigned to a NIC by the manufacturer. It is usually written in hexadecimal, grouped in pairs, for example 0A:1B:2C:3D:4E:5F. The first half often identifies the vendor; the second half is a serial number. MAC addresses operate at the data link layer and are used only for delivery within the local network segment (e.g. your home Wi-Fi or a school classroom VLAN).

Switches and wireless access points use MAC addresses to learn which device is on which port or radio association. Frames on Ethernet or Wi-Fi include a source MAC and a destination MAC. Devices ignore frames that do not match their MAC unless they are intended for all devices (broadcast) or the device is operating in a special mode (e.g. monitoring).

MAC vs IP: different jobs

Students often confuse MAC and IP addresses because both involve numbers and addressing. The key difference is scope: the MAC is a hardware address for the local link, while the IP address identifies a device’s location on an internetwork so data can be routed between networks. See the comparisons below.

MAC: usually fixed for the life of the NIC (some systems allow MAC randomisation for privacy when connecting to public Wi-Fi).
IP: may change when you move networks (home, school, café) or when the router allocates a new address via DHCP.

Switch: forwards frames based on MAC addresses within a single network segment.
Router: forwards packets between different networks based on IP addresses.

You open a webpage. Your device sends a frame to the gateway with destination MAC of the router and source MAC of your NIC. Inside that frame is an IP packet with the destination IP of the website and your device’s source IP. As the packet crosses the internet, the MAC addresses change at each hop, but the IP addresses remain the same end to end.

IP addressing: identifying a device across networks

What is an IP address?

An IP address is a numerical label assigned to each device that communicates over an IP network. It allows routers to decide where to send packets so they reach the correct destination network. The most common form you will see is IPv4 written as four decimal numbers separated by dots, e.g. 192.168.1.25. There is also IPv6, written in hexadecimal groups separated by colons, e.g. 2001:0db8:85a3::8a2e:0370:7334, which provides a vastly larger address space.

Key IP concepts you need

  • Network vs host part: an IP address is split into a network portion and a host portion so routers know which network to target and devices know who shares their local network.
  • Subnet mask (IPv4) or prefix length: defines how many bits are the network part. Example mask 255.255.255.0 or prefix /24 means the first 24 bits identify the network.
  • Default gateway: the router address your device uses to reach other networks (e.g. the internet).
  • DHCP: Dynamic Host Configuration Protocol automatically gives out IP addresses, the subnet mask, gateway and DNS settings to devices when they join a network.
  • Public vs private addresses: private ranges (e.g. 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16) are used inside homes and schools; public addresses are used on the wider internet.

Important contrasts

IPv4: 32 bits; about 4.3 billion addresses; widely used and easy to recognise. Often combined with Network Address Translation (NAT) due to limited supply.

IPv6: 128 bits; enormous address space; written in hexadecimal; supports features such as simpler autoconfiguration and efficient routing. Many networks support both forms.

Static: IP manually configured and constant; used for servers, printers or network equipment that must always be at the same address.

Dynamic (DHCP): IP assigned automatically for a time period (a lease); simpler for classrooms and portable devices.

Private addresses work only inside your local network. Your router translates them to a public IP when traffic goes to the internet.

Public addresses are reachable across the internet and must be globally unique. They are usually allocated to the router by the Internet Service Provider (ISP).

Routers: connecting networks together

Role of a router

A router connects two or more different networks and forwards packets between them based on IP addresses. In a home or classroom, the router connects the local area network (LAN) to the internet (the wide area network, WAN). It knows which IP networks are reachable on each interface and chooses the best next hop for each packet. Routers build or receive routing tables that map networks to the correct interface or next router.

What home/school routers commonly do

  • Routing: forwards packets between LAN and WAN according to IP addressing.
  • NAT (Network Address Translation): translates private LAN addresses to a single public address so many devices can share one internet connection.
  • DHCP server: automatically assigns IP settings to devices joining the LAN.
  • Firewalling: filters unwanted inbound traffic, improving security.
  • Wireless access point and switching (in many home units): allow wired and wireless devices to join the LAN.

Router decisions illustrated

Your laptop wants a webpage. It sends the packet to the default gateway (the router). The router translates your private IP to its public IP using NAT, forwards the packet to the ISP, and keeps a temporary mapping so replies are returned to your laptop.

Your phone sends a file to your laptop on the same Wi-Fi. The devices are in the same subnet. The phone finds the laptop’s MAC via ARP and sends frames directly through the switch/access point. The router is not needed for this local delivery.

Your laptop and a school printer are on different subnets (e.g. separate VLANs). The packet goes from your laptop to the router, which forwards it to the printer’s subnet based on the routing table. Access may be controlled by firewall rules between subnets.

Putting it together: from NIC to router to the world

  1. Your NIC formats data into frames and uses your MAC address on the local link.
  2. IP addressing gives your device a number that identifies it on the network and defines which network it belongs to.
  3. The router examines destination IPs and forwards packets towards the correct network, often translating addresses using NAT on the way to the internet.
  4. At each hop, frames are rebuilt with new source/destination MAC addresses appropriate for the new local link, but the source and destination IP addresses remain constant end to end.

Common classroom scenarios and choices

When you join a Wi-Fi network, your laptop sends a request to obtain settings. The router’s DHCP service offers an IP address, mask, gateway and DNS. Your NIC stores these and you are ready to access both local resources and the internet via the router.

A printer used by many people should keep the same IP so everyone’s shortcuts continue to work. Give it a static IP or configure a reserved DHCP lease. The router must route between subnets if the printer is on a dedicated VLAN for security.

Schools often use filtering or firewall rules on the router to block unsuitable sites or services. The same site may work at home because the home router has different policies. The difference is not your NIC or MAC; it is the router’s traffic rules.

Key terminology (quick reference)

Term Concise definition
NIC Hardware that connects a device to a network and handles data link functions.
MAC address Hardware address of a NIC used for local delivery on the same network segment.
IP address Logical address used by routers to send packets between networks.
Subnet mask / prefix Definition of which part of the IP is the network portion.
Default gateway The router a device uses to reach other networks.
DHCP Protocol that automatically provides IP configuration.
NAT Technique used by routers to map many private addresses to one public address.

 Key Takeaways

  • A NIC connects a device to the network and uses its MAC address for local frame delivery.
  • An IP address identifies a device across networks so routers can forward packets to the right destination.
  • MAC works at the local link and usually stays the same; IP may change when you join different networks or when DHCP renews.
  • Routers join networks together, use routing tables, often perform NAT, run DHCP and provide firewalling.
  • On each hop, MAC addresses change but the IP addresses remain end to end, enabling reliable delivery.
  • Choosing static or dynamic IPs, and understanding private vs public addressing, helps you troubleshoot typical classroom and home networking issues.