# network bridge

> device that creates a larger computer network from two smaller networks

**Wikidata**: [Q188635](https://www.wikidata.org/wiki/Q188635)  
**Wikipedia**: [English](https://en.wikipedia.org/wiki/Network_bridge)  
**Source**: https://4ort.xyz/entity/network-bridge

## Summary  
A network bridge is a device that connects two smaller computer networks to create a larger network. It operates at the data link layer (Layer 2) of the OSI model and forwards data based on MAC addresses. Bridges are used to segment networks and reduce traffic congestion while maintaining connectivity.

## Key Facts  
- A network bridge functions at Layer 2 (data link layer) of the OSI model.  
- It connects multiple network segments to form a single, larger broadcast domain.  
- Bridges use MAC addresses to make forwarding decisions.  
- Subclasses include filtering network bridges and LocalTalk-to-Ethernet bridges.  
- Defined in IEEE 802.1D standard.  
- Related but distinct from network switches, which also operate at Layer 2.  
- Used in both wired and wireless networking contexts.  
- Aliases include "bridging," "Netzwerkbrücke," "网桥," and "мост."  

## FAQs  
### Q: What is the purpose of a network bridge?  
A: A network bridge connects two or more network segments to expand the size of a network. It filters and forwards data frames between segments based on MAC addresses, helping manage network traffic efficiently.

### Q: How does a network bridge differ from a network switch?  
A: While both operate at Layer 2, a network bridge typically has fewer ports and simpler logic compared to modern switches. Switches often integrate advanced features like VLAN support and full-duplex communication, making them more scalable and efficient than traditional bridges.

### Q: Is a network bridge still relevant today?  
A: Yes, although largely replaced by network switches in modern LANs, bridges remain useful in specialized applications such as connecting legacy systems, virtual environments, and wireless-to-wired transitions.

## Why It Matters  
Network bridges played a foundational role in early local area network (LAN) design by enabling the expansion of networks without requiring routers or complex configurations. They helped manage collision domains and improved performance by isolating unnecessary traffic between segments. Though largely superseded by switches, their principles continue to influence how modern networking equipment handles segmentation and interconnection. Bridges also serve niche roles in virtualization platforms and protocol translation scenarios, ensuring compatibility across diverse network infrastructures.

## Notable For  
- Being defined under the IEEE 802.1D standard for transparent bridging.  
- Acting as a core component in extending Ethernet-based networks before switches became prevalent.  
- Supporting both physical media types and logical topologies through various implementations.  
- Providing basic Layer 2 functionality essential for understanding modern switching technologies.  
- Enabling integration between dissimilar network protocols, such as LocalTalk and Ethernet.

## Body  
### Functionality  
A network bridge operates at the data link layer (Layer 2) of the OSI model. Its primary function is to connect separate network segments and forward data frames based on Media Access Control (MAC) addresses. By inspecting incoming frame headers, a bridge determines whether to forward or filter packets, reducing unnecessary traffic within each segment.

### Standards and Protocols  
The operation of network bridges is standardized in IEEE 802.1D, which defines the Spanning Tree Protocol (STP), allowing redundant paths in switched networks without creating loops. Transparent bridging—where bridges learn MAC addresses dynamically—is another key feature outlined in this specification.

### Types of Bridges  
There are several types of bridges:  
- **Transparent Bridge**: Learns MAC addresses automatically and makes forwarding decisions accordingly.  
- **Source Route Bridge**: Commonly used with Token Ring networks, where the source node specifies the route taken by the frame.  
- **Filtering Network Bridge**: Limits traffic flow using access control lists or other filtering mechanisms.  
- **LocalTalk-to-Ethernet Bridge**: Connects Apple's legacy LocalTalk protocol to standard Ethernet networks.

### Relationship to Other Devices  
Unlike hubs, which simply repeat signals, bridges intelligently process and direct traffic. Compared to routers, they do not examine IP addresses or perform routing functions—they work strictly at the link layer. Modern equivalents include managed switches that offer enhanced capabilities like Quality of Service (QoS), VLAN tagging, and port mirroring.

### Applications  
Bridges are commonly found in:  
- Legacy system integrations  
- Wireless access point backhauls  
- Virtual machine networking (e.g., Linux bridges)  
- Industrial control systems requiring deterministic behavior  

Despite being less common in general-purpose networking today, bridges retain utility in specific technical niches due to their simplicity and reliability.

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  "name": "network bridge",
  "description": "Device that creates a larger computer network from two smaller networks.",
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## References

1. [Source](https://github.com/JohnMarkOckerbloom/ftl/blob/master/data/wikimap)
2. Freebase Data Dumps. 2013
3. Quora
4. National Library of Israel
5. [OpenAlex](https://docs.openalex.org/download-snapshot/snapshot-data-format)