These devices have distinct network roles: a switch connects devices within a LAN, a router connects networks, a modem links to an ISP's transmission system, a gateway connects dissimilar systems, and a firewall controls permitted traffic.
Roles of Network Devices
| Device | Main function | Mechanism |
|---|---|---|
| Switch | Connects devices within a local area network (LAN) | Forwards frames to the correct port using destination MAC addresses and a learned MAC address table. |
| Router | Connects separate networks | Forwards packets according to destination IP addresses and a routing table, usually between the LAN and internet. |
| Modem | Links a network to an internet service provider's system | Converts digital data into signals suitable for the transmission medium and converts received signals back. |
| Gateway | Connects networks or systems that may differ | Translates protocols, data formats, or architectures. A default gateway receives packets intended for another network and is commonly a router. |
| Firewall | Controls network access | Examines incoming and outgoing traffic, then permits or blocks it using rules based on IP addresses, ports, protocols, or connection state. |
These devices may be combined physically. A home “router” may include routing, an Ethernet switch, a wireless access point, a firewall, and sometimes a modem. Their logical functions remain distinct.
A common misconception is that a modem and router are identical. The modem supplies the service-provider link; the router directs packets between networks. Another misconception is that a firewall blocks all external traffic. It instead applies rules, allowing legitimate traffic while rejecting traffic that violates policy.
IB Exam Technique
For A2.1 Network fundamentals, define each device by its purpose and the information it uses. In a comparison, state that switches forward frames using MAC addresses, whereas routers forward packets using IP addresses. Do not define every gateway as a router: gateway is the broader function and may involve protocol translation.
