Network Devices Hub, Switch, Router, Gateway

Network Devices Overview

Network devices are hardware components that connect computers and other devices in a network, enabling communication and data transfer. Each device operates at a specific layer of the OSI model and serves a distinct purpose.

Device	OSI Layer	Function	Key Characteristic
Hub	Layer 1 (Physical)	Broadcasts data to all connected ports	No intelligence - creates a single collision domain; largely obsolete
Switch	Layer 2 (Data Link)	Forwards frames based on MAC address to the correct port only	Each port is its own collision domain; uses MAC address table
Router	Layer 3 (Network)	Routes packets between different networks using IP addresses	Connects LANs to WANs; uses routing tables; separates broadcast domains
Bridge	Layer 2 (Data Link)	Connects two network segments and filters traffic by MAC address	Reduces collision domains; software-based (slower than switch)
Gateway	Layer 7 (Application)	Translates between different network protocols or architectures	Can convert between TCP/IP and other protocols; most complex device
Repeater	Layer 1 (Physical)	Amplifies and regenerates signals to extend network range	No filtering; extends cable length; does not reduce collisions
Modem	Layer 1-2	Modulates/demodulates signals for transmission over telephone or cable lines	Converts digital signals to analog (and back); connects to ISP
Access Point (AP)	Layer 2 (Data Link)	Provides wireless connectivity to a wired network	Extends LAN wirelessly; uses IEEE 802.11 standards (Wi-Fi)
NIC (Network Interface Card)	Layer 1-2	Connects a computer to a network	Has a unique MAC address; can be wired (Ethernet) or wireless (Wi-Fi)

Hub vs Switch vs Router

Feature	Hub	Switch	Router
OSI Layer	1	2	3
Addressing	None	MAC address	IP address
Traffic handling	Broadcasts to all ports	Unicast to specific port	Routes between networks
Collision domain	Single (all ports)	Per port	Per interface
Broadcast domain	Single	Single (unless VLANs)	Per interface (separates)
Speed	Slow (collisions)	Fast	Slower (more processing)
Intelligence	None	MAC table	Routing table, NAT, DHCP

Layer 3 Switch vs Router

A Layer 3 Switch (multilayer switch) combines the functionality of a switch and a router:

Can route between VLANs at wire speed (hardware-based routing)
Faster than a traditional router for inter-VLAN routing
Used within enterprise LANs; routers used for WAN connectivity
Routers have more WAN interface options (serial, DSL, fiber)

Managed vs Unmanaged Switches

Feature	Unmanaged Switch	Managed Switch
Configuration	Plug-and-play, no config needed	Configurable via CLI, web, or SNMP
VLANs	Not supported	Supported
QoS	Not supported	Supported
Monitoring	None	SNMP, port mirroring, logging
Cost	Low	Higher
Use case	Home, small office	Enterprise, data center

Trace Traffic Through a Switch, Router, and Access Point

Laptop -> Wi-Fi access point: wireless link is bridged into the LAN
Access point -> switch: frame is forwarded using the destination MAC table
Switch -> default gateway: remote IP is sent to the router MAC
Router -> WAN: IP forwarding selects the next hop and may apply policy or NAT

Each device makes decisions at a different boundary; calling every device a router hides the failure location.

Count Broadcast and Collision Domains

One switch with four full-duplex hosts: four collision domains, one broadcast domain
Add a router interface and a second LAN: broadcasts stop at the router, creating another broadcast domain
Replace the switch with a hub: attached hosts share one collision domain

Modern switched Ethernet isolates collisions per port, while routing separates broadcast domains.

Before you move on