Lecture on Bridges in Computer Networks

Introduction

• Bridges are used to connect two different LANs
• Unlike hubs, bridges can connect different types of LANs (e.g., token ring and token bus)

Why is it Called a Bridge?

• Similar to physical bridges connecting two areas

Key Functions of Bridges

Forwarding

• Forward packets from one LAN to another if the destination MAC address is on a different side
• Works on the physical layer and data link layer
• Can check MAC addresses

Filtering

• Stops packets if the destination MAC address is on the same side
• Helps in reducing unnecessary traffic
• This feature is not available in hubs or repeaters

Types of Bridges

Static Bridges

• Maintains a fixed table with MAC addresses and port numbers
• Manual updates by network administrators are required
• Problems if MAC address or interface changes

Dynamic (Transparent) Bridges

• Starts with an empty table and learns MAC addresses over time
• Uses broadcasting initially to learn addresses
• Automatically updates the table, reducing the need for manual intervention

Static vs. Dynamic Bridges

• Static Bridges:
  • Require manual updates
  • No learning capability
• Dynamic Bridges:
  • Learn and update their table automatically
  • Take more time initially but perform better over time
  • No network administrator interference required

Collision Domain

• Bridges have a lower chance of collision compared to hubs and repeaters
• Use a store-and-forward strategy with their own buffer

Bridge Protocol Data Units (BPDU)

• Used to remove loops from the network
• Create a spanning tree to ensure packets do not get stuck in loops
• Helps in finding the correct path for packet forwarding

Importance

• Useful for UGC NET, PSU exams, and IT officer exams
• Less likely to be tested in GATE exams