An intermediary device is any networking device that sits between the computers, phones, or servers that actually send and receive data. Routers, switches, hubs, bridges, firewalls, and wireless access points all qualify. Their shared purpose is to move data from one place to another without being the origin or final destination of that data.
If you’re studying for a networking exam or just trying to understand how networks work, this distinction matters. End devices (like your laptop or a web server) create and consume data. Intermediary devices simply ensure that data gets where it needs to go.
Common Intermediary Devices
The most important intermediary devices you’ll encounter are routers and switches. Routers connect separate networks together and decide which path your data should take across the internet or between office locations. Switches operate within a single network, connecting computers, printers, and other devices in the same building or floor and directing traffic only to the specific device that needs it.
Beyond those two, several other devices fill intermediary roles:
- Hubs are older, simpler devices that broadcast incoming traffic to every connected port. They’ve largely been replaced by switches.
- Bridges connect two network segments and filter traffic between them. Like hubs, they’ve mostly been absorbed into modern switch functionality.
- Firewalls inspect and filter traffic based on security rules, sitting between your internal network and the outside world.
- Wireless access points provide Wi-Fi connectivity, acting as the bridge between wireless devices and the wired network.
Switches have essentially absorbed the roles of both hubs and bridges while adding significant performance improvements. They provide dedicated bandwidth to each connected device, support full-duplex communication (sending and receiving simultaneously), and process frames at much higher speeds using specialized hardware.
What Intermediary Devices Actually Do
Every intermediary device performs some combination of four core functions. First, they regenerate and retransmit data signals, which prevents the signal from degrading over long cable runs or multiple hops. Second, they maintain information about what pathways exist through the network, so they know where to send traffic. Third, they notify other devices of errors and communication failures. Fourth, they redirect data along alternate pathways when a link goes down.
Not every intermediary device handles all four tasks equally. A simple hub just regenerates signals and sends them everywhere. A router handles all four, actively choosing the best path for each packet and rerouting around failures.
How Switches and Routers Direct Traffic
Switches and routers use different methods to figure out where data should go, and this is one of the most important concepts in networking.
A switch builds a MAC address table. Every device on a network has a unique MAC address burned into its hardware. When a device sends data through a switch, the switch records which MAC address is connected to which physical port. The next time traffic arrives destined for that MAC address, the switch sends it directly to the correct port instead of flooding it everywhere. This is why switches are so much faster and more efficient than hubs.
A router works with IP addresses instead. When a packet arrives, the router checks its routing table to find the best next hop toward the packet’s destination IP address. At each hop along the way, the router rewrites the frame with new source and destination MAC addresses appropriate for that specific link, while the IP addresses stay the same end to end. This process repeats at every router until the packet reaches the network where the destination device lives.
Where They Sit in the OSI Model
If you’re studying the OSI model, the layer a device operates at tells you what kind of information it uses to make decisions. Hubs operate at Layer 1 (the physical layer), dealing only with electrical signals. Switches and bridges operate at Layer 2 (the data link layer), using MAC addresses to forward frames. Routers operate at Layer 3 (the network layer), using IP addresses to forward packets across different networks.
This layering explains why routers and switches behave so differently. A switch only needs to look at the MAC address in each frame to decide which port to send it out. A router needs to examine the IP address, consult its routing table, and potentially choose between multiple possible paths.
Intermediary Devices vs. End Devices
The defining difference is simple: end devices originate or consume data, while intermediary devices just move it along. Your laptop, a web server, a smart thermostat, and a network printer are all end devices. They are the source or destination of network communication.
Intermediary devices work behind the scenes. They connect individual end devices to the network and connect multiple networks to form larger internetworks. You interact with end devices directly. You rarely think about intermediary devices at all, unless something breaks.
Role in Local vs. Wide Area Networks
Intermediary devices serve different roles depending on the size of the network. In a local area network (LAN), switches are the primary intermediary devices, providing high-speed connections between nearby devices. A typical office LAN might use one or more switches to connect all the computers on a single floor.
Wide area networks (WANs) rely heavily on routers to interconnect LANs across cities, countries, or continents. WAN links are typically slower than LAN connections, which makes the router’s ability to choose efficient paths and reroute around failures even more critical. In most real-world networks, switches handle the local traffic while routers handle communication between distant locations.