What Are Bridges in Networking? (Plus Types and Uses)

By Indeed Editorial Team

Published August 3, 2022

The Indeed Editorial Team comprises a diverse and talented team of writers, researchers and subject matter experts equipped with Indeed's data and insights to deliver useful tips to help guide your career journey.

Bridges combine two or more networks to form a larger network. They connect different components of the individual networks and make them work like those of a single network. If you're planning to pursue a career in computer networking, it can be helpful to learn about bridges.

In this article, we discuss what bridges in networking are, what they do, what different types of bridges are, what their uses are and what forwarding methods they use.

What are bridges in networking?

Bridges are the devices used to combine multiple networks into a larger network. They're different from routers in that they make multiple networks work like one, whereas routers let the networks communicate independently. Bridges are preferable over network hubs, which are the nodes or connection points that broadcast the incoming data on all the connected devices.

Unlike hubs, bridges don't broadcast the data. Instead, they filter and forward the data. You can use bridges to connect wired or wireless networks or any combination thereof.

According to the Open Systems Interconnection (OSI) model, computers use seven different layers for data communication in a network. The second layer is called the data link layer. It defines the format of the data. Bridges work at this layer of the network.

Read more: 12 Computer Networking Basics You Should Know for an IT Job

What do bridges do in computer networking?

Bridges aggregate multiple computer networks and make them work like one. They extend the physical coverage of local area networks. They achieve this by dividing local area networks (LANs) into multiple segments.

In computer networking, each hardware manufactured has a unique ID assigned to it, which is commonly known as a media access control (MAC) address. Communication between devices takes place based on their MAC addresses.

A network bridge reads the MAC address of the destination device from an incoming frame of data and searches for the destination device on the network. If it determines that the destination address is on the network, it forwards the data to the relevant segment of the network. If it doesn't find the destination address on the network, it blocks the data.

Read more: Everything You Need To Know About Computer Networking

Types of bridges

Following are the main types of network bridges:

Transparent bridges

A transparent bridge remains invisible in the network in that other devices don't get to know about its existence. Transparent bridges automatically create a table of MAC addresses just like a routing table while connecting two or more networks. This table is commonly known as a forwarding information base.

Transparent bridges are capable of merging several bridges to analyze the incoming traffic. Networking professionals mainly use these bridges in Ethernet networks, which are a common type of wired connections used in computer networking.

Transparent bridges use both source and destination addresses. They record the source addresses in the forwarding information base. They look up the destination addresses to determine whether the destination segment exists on the network. Transparent bridges update their forwarding information base with the source addresses of each data frame they receive. They're also known as learning bridges. They can operate devices with two or more two ports.

Translational bridges

A translational bridge can connect different types of networks, such as Ethernet and token ring networks. A token ring network is one that transmits data in one direction through several locations using a special data frame called a token. Translational bridges can add or remove the data fields based on the direction of the data.

Since they translate the received data to facilitate communication between different types of network protocols, they are commonly called translational bridges.

Simple bridges

A simple bridge is a type of transparent bridge used to connect two network segments. It determines whether to forward a data frame to another segment based on each data frame it receives. It uses the store and forward technique, meaning that it sends the information to an intermediate station, which stores the information and sends it to the final destination at a later time.

Simple bridges verify the integrity of the data frames on the source network and accommodate the data transmission delays at the destination network. These delays are usually caused when an Ethernet has to wait for other stations to stop transmitting data.

Multiport bridges

A multiport bridge is one that connects more than two networks. Just like a simple bridge, it also operates transparently and determines whether to forward the traffic to another segment of the network individually for each data frame. It uses the store and forward technique to transmit data.

Source-route bridges

Source-route bridges connect two similar segments of the network. Networking professionals use these bridges especially for connecting token ring networks. In this type of bridge, the sending station knows about all the existing bridges in the network and determines the destination route before transmitting the data.

Source-route bridges are helpful in preventing looping problems. Looping problems occur when there are multiple active paths between the source and the destination, which may cause the data to keep traveling in the same route. Network loops often slow down the network. They may even cause the complete failure of the network.

MAC-layer bridges

A MAC-layer bridge combines similar types of network segments. It filters the data packets and removes or broadcasts the incoming traffic to the destination port on its own. It's also called a local bridge. A MAC-layer bridge lets you have a direct connection between home network devices and a wide area network (WAN). It doesn't require access to LAN since it gets an IP address directly from your internet service provider.

MAC-layer bridges can be helpful in operating a home server or Internet of Things (IoT) devices. IoT is a network of devices, such as refrigerators, washing machines and air conditioning systems that are connected to the internet and can communicate over a wireless network on their own.

Remote bridges

A remote bridge connects two networks located at different geographical locations. It connects local area networks using WAN protocol, such as modems and leased lines. Its speed varies based on the LAN and WAN connections. It uses an internal buffer to hold the data it receives from LAN. A remote bridge usually has at least two ports, or connecting points–one LAN port, such as RJ-45, and one serial port, such as RS-232. You can connect a remote bridge to the main switches of LANs and connect the modem to the serial port.

Shortest path bridges

A shortest path bridge routes traffic through the shortest path to the destination segment. It blocks all the redundant paths that may create a loop in the data link layer. It improves the efficiency of the network by routing data through multiple paths. It's capable of using all the available options of physical connectivity.

Read more: Networking vs. Programming: Definitions and Differences

Uses of bridges

Following are some of the main uses of networking bridges:

Multiply network capacity

Bridges combine multiple LANs to make a larger LAN. They multiply the network's capacity and coverage. Wireless bridges facilitate data transmission to remote geographical locations by connecting multiple networks together. Having a larger network reduces the sudden traffic loads in a network because the traffic gets distributed uniformly over a larger network.

Improve network performance

A network bridge can divide a large, busy network into multiple segments, such that each segment acts as a separate collision domain, which is a place where simultaneous data transmissions take place. This reduces the number of data collisions in the network. There's a separate bandwidth associated with each collision domain, which improves the network performance.

Prevent breakdown of the network

Network bridges prevent the breakdown of the network when there's a fault in any single node. When a bridge detects a faulty node, it discards the data frame destined toward the node or forwards it to some other node.

Provide functional support

Transparent bridges provide complete functional support to a computer network. They don't require any major updates in terms of hardware or software for installation. They help determine whether the data frames received are to be blocked or forwarded to some other segment of the network.

They forward the data frames only when a MAC address exists in the network. You can also use them to broadcast the frames even when the destination MAC address doesn't exist in the network. They maintain a table of MAC addresses of the entire network.

Read more: What Is a Data Set? (With Definition, Components and Types)

What are the different forwarding methods a network bridge uses?

A network bridge uses the following four methods to forward data:

  • Store and forward: In this method, a bridge receives a data frame and stores it. It then verifies the frame and forwards it.

  • Cut through: In this method, a bridge starts forwarding a data frame as soon as it receives the destination address. It doesn't check the frame for errors.

  • Fragment free: This method combines the benefits of the store and forward and cut through methods. A bridge checks the first 64 bytes and leaves the remaining error check to the destination device.

  • Adaptive switching: In this method, a bridge automatically selects one of the above three forwarding methods.

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