🌐 Networking Devices (Part 2) – Bridges, Switches, and Routers | CN#5

In CN4, we explored cables, repeaters, and hubs. Now, let’s move to smarter devices that don’t just forward blindly — they actually analyze and decide how data flows.

🔹 Bridge

🔸 What is a Bridge?

A bridge is a device that connects two or more LAN segments. Unlike hubs (which broadcast data everywhere), a bridge can look at the MAC address of each frame and decide whether to forward it or not.

• Works at Layer 2 (Data Link Layer).

• Introduced to reduce collisions and unnecessary traffic.

  

🔸 How it Works

When a frame comes in:

1. The bridge checks the destination MAC address.

2. If the destination is on the same segment → it filters (doesn’t forward).

3. If the destination is on another segment → it forwards the frame only there.

4. Over time, it builds a MAC address table (like a memory map of which devices are connected to which port).

🔸 Technical Details

• Number of Ports: Usually 2 (but can be more).

• Forwarding? ✅ Yes, based on MAC address.

• Filtering? ✅ Yes, prevents unnecessary traffic.

• Collision Domains: 1 per port (so if a bridge has 2 ports, it has 2 separate collision domains).

• Broadcast Domains: Still 1 (doesn’t break broadcasts).

🔸 Real World Example

Imagine an apartment building with two wings. A security guard (bridge) only lets residents cross wings if they actually need to go there, instead of allowing everyone to run around.

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🔹 Switch

🔸 What is a Switch?

A switch is essentially a multi-port bridge, but much smarter and faster. It connects multiple devices and forwards frames only to the specific port where the destination device is.

• Works at Layer 2 (some advanced ones at Layer 3 = “Layer 3 switches”).

• Reduces both collisions and unnecessary traffic.

🔸 How it Works

1. Maintains a MAC Address Table for all connected devices.

2. When a frame arrives, the switch looks up the MAC address.

3. Forwards only to the correct port, not to everyone.

4. Operates in full-duplex mode (no collisions).

🔸 Technical Details

• Number of Ports: 4–48 (common), can be stacked for hundreds.

• Forwarding? ✅ Yes, MAC-based.

• Filtering? ✅ Yes, blocks irrelevant frames.

• Collision Domains: 1 per port (so a 24-port switch = 24 collision domains).

• Broadcast Domains: Still 1 (unless VLANs are configured).

🔸 Real World Example

Think of a post office clerk who knows which desk each employee sits at. Instead of shouting, the clerk quietly hands your parcel to the right person.

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🔹 Router

🔸 What is a Router?

A router is the brain of networking. Unlike bridges and switches, which only look at MAC addresses, a router looks at IP addresses and decides the best path to forward packets across different networks.

• Works at Layer 3 (Network Layer).

• Used to connect LANs to WAN (e.g., home network to the Internet).

🔸 How it Works

1. Reads the destination IP address in the packet.

2. Uses a routing table (like a map) to determine where to forward it.

3. Can perform Network Address Translation (NAT), firewall filtering, and traffic prioritization.

4. Separates both collision and broadcast domains.

🔸 Technical Details

• Number of Ports: Typically 2+ (LAN + WAN), enterprise routers can have dozens.

• Forwarding? ✅ Yes, based on IP addresses.

• Filtering? ✅ Yes, applies access control and routing policies.

• Collision Domains: 1 per port.

• Broadcast Domains: Each interface is a separate broadcast domain (unlike switches).

🔸 Real World Example

Think of Google Maps: It doesn’t just tell you which street is nearby (like a switch), it figures out the best route across cities to get you to your destination.

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📊 Comparison Table

✅ Stay tuned for CN #6: Exploring the OSI Model!
🧵 Follow the entire CN series to master networking step-by-step.