Routers, Switches, Hubs, Bridges & Gateways
Exam-focused notes on network devices for SSC, Banking (IBPS/SBI), Railway, UPSC, NIELIT, JAIIB/CAIIB and IT officer papers. Learn OSI layers, functions, uses, collision vs broadcast domains, comparisons, and practice with interactive MCQs.
Why Network Devices Matter in Exams
One of the highest-frequency Computer Networks topics
Network devices connect computers and move data. Exams almost always ask: which OSI layer?, MAC or IP?, and hub vs switch vs router.
1. Router
Connects different networks using IP addresses
Router
OSI Layer 3 · Network Uses IPA router connects different networks (for example LAN ↔ Internet) and forwards packets to the correct path using IP addresses.
Key functions
- Works at Network Layer (Layer 3)
- Forwards packets using IP addresses
- Builds/uses routing tables
- Often supports NAT, DHCP, firewall/ACL
- Separates broadcast domains
Uses / examples
- Home/office LAN to Internet
- Routing between subnets/VLANs (with L3)
- Branch office WAN connectivity
- Default gateway for PCs
Exam hot points
- Layer 3 device
- IP-based forwarding
- Connects different networks
- Does not forward broadcasts between networks
Not mainly for
- Replacing a pure LAN switch role
- MAC-only frame switching as primary job
- Simple signal repeating (that is hub/repeater)
2. Switch
Smart LAN connector using MAC addresses
Switch
OSI Layer 2 · Data Link Uses MACA switch connects devices inside a LAN and forwards frames to the correct port using MAC addresses.
Key functions
- Works at Data Link Layer (Layer 2)
- Learns MACs into a MAC/CAM table
- Each port ≈ own collision domain
- Supports VLANs (managed switches)
- Much smarter and faster than a hub
Uses / examples
- Office LAN: PCs, printers, servers
- Reduces congestion vs hub
- PoE switches power phones/cameras
- Data centre high-speed switching
Exam hot points
- Layer 2 · MAC based
- Unknown MAC → flood in VLAN
- STP prevents loops
- L3 switch = switch + routing features
Switching methods
- Store-and-forward: full frame + CRC check
- Cut-through: faster, lower latency
- Store-and-forward reduces bad-frame spread
3. Hub
Old, dumb multi-port repeater
Hub
OSI Layer 1 · Physical LegacyA hub is a basic device that connects multiple devices and broadcasts incoming data to all ports. It has no intelligence to choose a destination.
Key functions
- Works at Physical Layer (Layer 1)
- Repeats signal to every port
- One shared collision domain
- No MAC table, no IP routing
Drawbacks
- More collisions, lower efficiency
- Shared bandwidth
- Less secure (easy sniffing)
- Mostly obsolete today
Exam hot points
- Layer 1
- “Dumb connector”
- Broadcasts to all devices
- Replaced by switches
Uses
- Very small/old LANs
- Low-cost legacy setups
- Rare in modern networks
4. Bridge
Connects and filters LAN segments at Layer 2
Bridge
OSI Layer 2 · Data Link Uses MACA bridge connects two (or more) LAN segments so they work as one network, while filtering traffic using MAC addresses.
Key functions
- Layer 2 device
- Filters/forwards frames by MAC
- Reduces unnecessary traffic between segments
- Creates separate collision domains per segment
Uses
- Extend a LAN
- Segment a busy network
- Join wired segments intelligently
Exam hot points
- Layer 2 like switch
- Switch = multiport bridge
- Not a Layer 3 router
- “Traffic controller” between segments
Bridge vs Switch
- Bridge: fewer ports, older concept
- Switch: many ports, hardware-fast
- Same basic MAC filtering idea
5. Gateway
Entry/exit point and protocol translator
Gateway
Multiple layers TranslatorA gateway connects networks that may use different protocols or architectures. It can translate protocols, formats, or addresses and acts as an entry/exit point.
Key functions
- Works at multiple OSI layers (often up to Application)
- Protocol / data format translation
- Network entry and exit point
- May include routing + security services
Uses / examples
- Enterprise edge to Internet
- IPv4 ↔ IPv6 translation scenarios
- Email-to-SMS / application gateways
- Home “Wi-Fi gateway” multi-function box
Exam hot points
- Translator between different systems
- Not limited to one OSI layer
- Default gateway on PC = router IP for outside traffic
- More than “just a switch”
Default gateway (host setting)
- IP of the router used for non-local traffic
- If wrong, Internet fails but local LAN may work
Collision Domain vs Broadcast Domain
Favourite comparison set in competitive exams
Collision domain
Area where simultaneous transmissions can collide.
- Hub: all ports = 1 collision domain
- Switch/Bridge: each port usually own collision domain
- Router: separates networks (no shared L2 collision across sides)
Broadcast domain
Area where a broadcast frame is flooded.
- Hub/Switch (same VLAN): one broadcast domain
- VLAN: splits broadcast domains on a switch
- Router: separates broadcast domains
Quick Comparison Table
Revise this table first before MCQs
| Device | OSI Layer | Address used | Main function | Typical use |
|---|---|---|---|---|
| Hub | 1 Physical | None (signal only) | Broadcast to all ports | Old/simple LAN |
| Repeater | 1 Physical | None | Regenerate/extend signal | Long cable runs |
| Bridge | 2 Data Link | MAC | Filter/forward between segments | Segment/extend LAN |
| Switch | 2 (L3 switch also 3) | MAC (IP if L3) | Smart LAN forwarding | Modern office LAN |
| Router | 3 Network | IP | Route between networks | LAN ↔ Internet / WAN |
| Gateway | Multiple | Depends | Protocol/network translation | Dissimilar networks / edge |
Related Devices (Short Notes)
Repeater
Layer 1. Regenerates weak signals to extend distance. No filtering.
Modem
Modulates/demodulates signals for ISP links (e.g., broadband). Often built into home gateways.
NIC
Network Interface Card — end-device hardware to connect to the network (has MAC).
Access Point (AP)
Provides Wi-Fi access to a wired LAN (Layer 2 role in many exam answers).
Firewall
Filters traffic by policy; often at network edge with router/gateway functions.
Layer 3 Switch
Switch + routing features; common for inter-VLAN routing in enterprises.
One-Glance Quick Revision
Hub
L1 · broadcasts all · one collision domain
Switch
L2 · MAC table · smart LAN
Bridge
L2 · filters segments · multiport→switch
Router
L3 · IP · different networks
Gateway
Multi-layer · protocol translator
Default gateway
Router IP for outside traffic
Collision domain
Broken by switch ports
Broadcast domain
Broken by router / VLAN
STP
Stops Layer 2 loops
VLAN
Logical broadcast domains on switch
NAT
Usually on router/gateway
L3 switch
Switch + router features
Practice MCQs on Network Devices
Tap any option to reveal the correct answer and a short explanation.
Exam Tips
Layer first
If options include devices, map Layer 1/2/3 immediately. That alone solves many MCQs.
MAC vs IP
MAC → switch/bridge. IP → router. “Different networks” → router/gateway.
Hub red flags
Words like broadcast to all, collisions, shared bandwidth, insecure sniffing → Hub.
Switch vs Bridge
Same layer idea. Switch is multiport/high-speed version of bridge concept.
Gateway wording
If question says different protocols/systems/translation → Gateway. If only IP path between nets → Router.
Domains one-liner
Switch breaks collision domains. Router breaks broadcast domains. VLAN also splits broadcasts.
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