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Bridging, in the context of networking, refers to the process of connecting two or more networks together so they can communicate. The device used to perform this function is typically called a bridge.

A network bridge operates at the data link layer (Layer 2) of the OSI (Open Systems Interconnection) model. It inspects incoming network traffic and determines whether to forward or discard it according to its destination address.

Here are some important aspects of bridging:

  1. Transparent Bridging: This is the most common type of bridging used today, and it’s commonly used in Ethernet networks. Transparent bridges can learn the network’s structure by analyzing the source addresses of frames that it sees on the network.
  2. Learning Process: The bridge maintains a database, usually called a forwarding table, that it uses to decide whether to forward or filter the frames it receives. It learns which addresses are on which network segment by examining the source addresses.
  3. Spanning Tree Protocol: If you connect bridges to create loops in the network for redundancy, you could create broadcast storms. The Spanning Tree Protocol (STP) is used to prevent loops in the network by creating a spanning tree that defines a single path for traffic.
  4. Types of Bridges: There are several types of bridges including simple bridges (which forward data), multiport bridges (which can connect multiple networks), and learning bridges (which can learn the difference between different network segments).

A bridge can connect dissimilar types of network segments (such as Ethernet and Fast Ethernet), and it can do so with a minimal impact on network performance. However, switches have largely replaced bridges in modern networks due to their ability to connect a larger number of nodes and their support for more advanced features.

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