Bridge in Computer Network

• A Bridge is a networking device that connects two or more LAN segments and forwards data between them. It works mainly at the Data Link Layer (Layer 2) of the OSI Model. 
• It uses MAC addresses to decide whether a frame should be forwarded or filtered while operating at the Data Link Layer (Layer 2) of the OSI architecture. 
• A bridge helps cut down on pointless traffic and enhance network performance by splitting a network into several collision domains. 
• Bridging is the process of utilizing a bridge to connect network parts.

Diagram

Types of Bridges 

There are three types of bridges in computer networks, which are as follows

• Transparent Bridge: Other networked devices cannot see transparent bridges. When a station is added or removed, this bridge does not reconfigure the network. The primary purpose of the transparent bridge is to either forward or block data based on the MAC address. 
• Source Routing Bridge: IBM created source routing bridges especially for token ring networks. The source station performs the routing operation by embedding the frame's whole route with the data frames, requiring the frame to follow a predetermined path or route once it is forwarded. 
• Translational Bridge: Translational bridges transfer data from one networking system to another. Alternatively, it is employed for data transmission or communication between two distinct kinds of networking systems. 

How Does a Bridge Work?

A bridge examines the MAC address of incoming data frames and decides whether the frame should be:

• Forwarded to another network segment.
• Filtered if the destination is on the same segment.

For example:

PC1 ─── LAN 1 ─── Bridge ─── LAN 2 ─── PC3
                     │
              Checks MAC Address

• If PC1 sends data to PC3, the bridge checks PC3's MAC address and forwards the frame to LAN 2.
• If PC1 sends data to PC2 and both are on LAN 1, the bridge can filter the frame instead of sending it to LAN 2.

Main Functions of a Bridge

1. Connects LAN segments.
2. Works at the Data Link Layer (Layer 2).
3. Uses MAC addresses to make forwarding decisions.
4. Filters unnecessary traffic.
5. Helps reduce network traffic and collisions.
6. Learns and maintains a MAC address table.

Simple Example

Imagine two classrooms connected through a bridge:

Classroom A                    Classroom B
PC1 ── PC2 ──┐              ┌── PC3 ── PC4
             │              │
             └── BRIDGE ────┘

Advantages:-

• The bridge allows computers in both classrooms to communicate while preventing unnecessary traffic from being transmitted to the other classroom.
• Bridges can serve as a network extension by joining two different network topologies. 
• It has more bandwidth because it has a distinct collision domain. 
• When distinct MAC protocols are present for various segments, it may generate a buffer. 
• incredibly dependable and maintained. There are several LAN segments that can be created from the network. 
• Easy to install, using only the bridge itself and no additional hardware or software. 
• The transparency of the protocol is greater than that of other protocols. 

Disadvantages:-

• Costly in comparison to repeaters and hubs.
• Reduce your speed. 
• Poor performance because viewing the network device's MAC address requires additional processing. 
• Individual data filtering is not feasible because the traffic is broadcast or received in large quantities. 
• The network experiences heavy broadcast traffic while data is being broadcast, and broadcast storms may develop. 

Bridge vs Switch

• A switch can be considered a more advanced version of a bridge. A traditional bridge usually connects a small number of network segments, whereas a switch commonly provides many ports and performs the same basic Layer-2 forwarding function.

In short:

A Bridge is a Layer-2 networking device that connects LAN segments and forwards or filters frames using MAC addresses.