Full width home advertisement

Electronics Hub

Internet of Networks

Post Page Advertisement [Top]

A transparent bridge is a bridge (Network Device) that specifically monitors incoming network traffic to identify media access control (MAC) addresses of the hosts. These bridges are operated in such a way that is transparent to all the network's connected hosts, which is why it is called a "Transparent".

According to IEEE 802.1d specifications,

A system equipped with a transparent bridge must fulfill the three requirements, such as:
  • Frames must be forwarded from one station to another. 
  • The forwarding table is automatically made by the learning process of frame movements in the network. 
  • Loops in the system must be avoided.

Transparent bridges maintain a list of MAC addresses, as do routers, but based on all the received frame’s source data-link MAC addresses. They use dynamic algorithm to accomplish this. The algorithm has five sections, such as:

Forwarding: A transparent bridge must forward correctly the frames to the ports connected to the hosts.

Learning: The bridge can recognize or learn the destination address of a frame by checking the response from the receiving host.

Filtering: After the learning process, the bridge determines the destination address of a frame and makes an entry into the forwarding table contained by the host. This is called filtering.

Flooding: At first, the bridge forwards the frames to every single hosts since it doesn’t know the destination address, this situation is “flooding”.

Avoiding Loops: The bridge must forward the frames in such a way, that it doesn’t make any unnecessary loops among the hosts.
transparent plastic, transparent background
Transparent bridge
Taken from the picture above,

Let us assume there are three hosts, A, B and C, and a bridge with three ports. 

1. Host A is connected to Bridge Port 1, Host B is connected to Bridge Port 2 and Host C is connected to Bridge Port 3. 

2. Host A sends a frame to the bridge that is addressed to Host B (Forwarding). 

3. The bridge checks the frame's source address and creates an address and port number entry for Host A in its forwarding table (Learning). 

4. The bridge then examines the frame's destination address, but does not find it in its forwarding table. As a result, the bridge over here sends the frame to all available other ports (2 and 3). This is called Flooding

5. The frame is then received by Host B and Host C, which also check the destination address. Host B identifies the destination address match and sends a response to Host A.

6. On the return path, the bridge adds an address and port number entry for Host B to its forwarding table

The bridge already has Host A's address in its forwarding table so it forwards the response only to Port 1. In this way, none of the Port 3 hosts are burdened with response requirements. Through this process, two-way communication between Host A and Host B is facilitated without the need for further flooding.

Note: Transparent bridge is often called “Adaptive bridge”, because it learns which node is connected to which port by examining the packets that are transmitted.

Study Sessions

Q1. What is a Transparent Bridge? What is the difference between a bridge and a transparent bridge?

Q2. What is flooding? Why does it occur? And how it can be solved

Q3. Why transparent bridge is often called an "Adaptive Bridge"?


No comments:

Post a Comment

Bottom Ad [Post Page]

| Designed by Sriparna Sarkar