Bridge is a network device that is used to separate LAN into number of section.

Bridge is also a computer networking device and it works on the Data Link Layer of The OSI L Model. The bridge sends packets between two network segments that use the same communication protocol. The bridge has two ports, one incoming and the other outgoing, so that the other part of the network is connected. The bridge checks the destination address before sending the data. If the destination was in another part of the network of MAC Network, then sends the data. Means the bridge has to decide whether to send the data packets to the other side of the Ethernet segment or not.

It operates both physical as well as data link layers of OSI modal.


- This device communicates the traffic present in the -local area network (LAN) to different parts.

-It protects the MAC address. Due to which there is proper management of network traffic.

-The bridge works in the data link layer in the OSI model of the bridge network.

Let us now know how these network bridges work. Bridge devices inspect incoming network traffic and determine whether to forward packets or discard them, depending on their destination. An Ethernet bridge, for example, first inspects each incoming Ethernet frame, including the source and destination MAC addresses—sometimes frame size—as it processes individual forwarding decisions.

This network bridge works in layer 2, which is the data link layer of the OSI model. It connects multiple network segments in this layer. Bridge does not only broadcast traffic from one network segment to another, but it also manages the traffic together.


There are four types of bridge -

(i) Transparent Bridge 

(ii) Source Routing Bridge 

(iii) Transparent Learning Bridge 

(iv) Transparent Spanning Tree Bridge

1. Transparent Bridges

These are those bridges in which the stations are completely unaware of the existence of the bridge, which means whether a bridge has been added to the network or has been deleted, so reconfiguration of these stations would have been absolutely unnecessary.

These bridges mainly use only two processes i.e. bridge forwarding and bridge learning.

2. Source Routing Bridges

In these types of bridges, the routing operation is performed by the source station and the frame itself determines which route they have to follow.

In this, the host can discover the frame if he wants, for this just a special frame has to be sent, which is called the discovery frame. Which gets spread throughout the network in all possible paths, which are linked to the destination.

3. Transparent Learning Bridge

This transparent bridge traces the location of the user through the source and destination address. When the frame is received in the bridge then it checks their source address and destination address.

In this the destination address is stored if it is not found in the routing table. Then the frame is sent to all LANs in which only those LANs are excluded from where that frame comes.

Also the source address is stored in the routing table. If another frame is reached where the previous source address is now its destination address, then it is forwarded to that port.

The physical topology of Transparent Bridges does not allow loops in the network. This is the restriction that happens over the transparent learning bridge.

4. Transparent Spanning Tree Bridge

The last type of bridge is the transparent spanning bridge. These bridges use the entire topology of a subnet so that they can create a loop free operation.

In this the received frame is checked in the same way as given below. The destination address of the Arrived frame is checked with the help of routing table which is located in the database. It requires more information, so the bridge port is also stored in the database.


- By using bridge devices we can extend network.

- It broadcast the data to each node like HUB and repeater.

- Collision can be reduced easily 

- It divides the traffic of the network.

- It speeds up the network traffic.

- This minimizes unnecessary collisions in the network.


-  It does not stablish connection between two different layers.

- Once it broadcasts the messages than it is incapable to stop the messages.

- It is not effective for reading IP addresses in the network.

- It is limited to local area network only.

- It is not efficient for handling complex network traffic.

- Its cost is more than the repeater.

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