What is a Network Bridge?

What is a network bridge?

A network bridge is a device or software that connects and filters traffic between two or more network segments, creating a single, unified network. It operates at the data link layer (Layer 2) of the OSI model and is used to reduce network congestion and improve performance by managing the flow of data. Here are key functions and features of a network bridge:

  1. Traffic Filtering: Bridges inspect incoming network traffic and decide whether to forward it or filter it out based on the MAC (Media Access Control) addresses of the devices.
  2. Collision Domain Reduction: By dividing a network into segments, bridges reduce the number of collisions, improving overall network efficiency.
  3. Network Extension: Bridges can connect different types of physical media (e.g., Ethernet to Wi-Fi) or extend the reach of a network by connecting multiple segments.
  4. Transparent Bridging: Most modern bridges use transparent bridging, where they automatically learn the MAC addresses of devices on each segment and build a forwarding table to decide how to route traffic.
  5. Loop Avoidance: To prevent loops in the network, which can cause broadcast storms, bridges use the Spanning Tree Protocol (STP) to create a loop-free logical topology.

Bridges are less commonly used today with the advent of more advanced devices like switches, which offer similar functionality but with greater efficiency and additional features.

What is a network bridge vs. router?

A network bridge and a router serve different purposes in a network, and they operate at different layers of the OSI model. Here are the key differences between the two:

Network Bridge

  • OSI Layer: Operates at the Data Link Layer (Layer 2).
  • Function: Connects and filters traffic between different segments of a network. It helps in extending the network and reducing traffic by filtering packets based on MAC addresses.
  • Traffic Handling: Uses MAC addresses to determine the destination of traffic. It forwards or filters traffic within the same network.
  • Use Case: Typically used to extend a local area network (LAN) and to reduce collision domains by segmenting the network.
  • Example: Connecting two separate LAN segments to form a single LAN.


  • OSI Layer: Operates at the Network Layer (Layer 3).
  • Function: Connects different networks and routes traffic between them. It determines the best path for data to travel across networks.
  • Traffic Handling: Uses IP addresses to determine the destination of traffic. It can route traffic between different IP networks.
  • Use Case: Used to connect multiple networks, such as connecting a home or office network to the Internet. Routers are essential for directing traffic on the Internet.
  • Example: Connecting a home network to the Internet Service Provider (ISP) network.

Key Differences

  1. Layer of Operation:
    • Bridge: Operates at Layer 2 (Data Link Layer).
    • Router: Operates at Layer 3 (Network Layer).
  2. Addressing:
    • Bridge: Uses MAC addresses.
    • Router: Uses IP addresses.
  3. Network Scope:
    • Bridge: Works within the same network to extend it or segment it.
    • Router: Connects different networks and routes traffic between them.
  4. Functionality:
    • Bridge: Filters and forwards traffic within a single network based on MAC addresses.
    • Router: Determines the best path for data to travel across multiple networks based on IP addresses and routing tables.
  5. Complexity:
    • Bridge: Simpler device with fewer features.
    • Router: More complex, with capabilities such as Network Address Translation (NAT), firewall functions, and Quality of Service (QoS).

In summary, while both devices are used to connect different parts of a network, bridges work within a single network to extend or segment it, whereas routers connect different networks and manage traffic between them.

Is a network bridge still used?

Yes, network bridges are still used, although their role has largely been superseded by more advanced networking devices like switches and routers. Here are some contexts where network bridges are still relevant:

  1. Legacy Systems: In older networks that were originally built using bridges, replacing them might not be necessary if they are still functioning well.
  2. Simple Network Extension: For small-scale network extensions where complex functionalities are not required, a network bridge can be a simple and cost-effective solution.
  3. Specific Network Topologies: In certain network topologies, especially where segmentation of the network is needed to reduce collisions without the need for the more advanced features of switches, bridges can still be effective.
  4. Wireless Bridging: In some wireless networking scenarios, bridges are used to connect different wireless segments or to extend wireless networks.
  5. Educational Purposes: For learning and educational environments, network bridges are often used to teach the fundamentals of networking.

Alternatives and Modern Uses

  • Switches: Most of the functionality of network bridges has been incorporated into switches. Switches perform the same basic function as bridges but with more efficiency and additional features.
  • Virtual Bridges: In virtualized environments, software-based network bridges are used to connect virtual machines and manage traffic between virtual network segments.
  • Network Segmentation: While physical bridges might be less common, the concept of network segmentation they provide is still relevant and often implemented using VLANs (Virtual Local Area Networks) on modern switches.


While the traditional physical network bridge is less common in modern networking setups due to the prevalence of switches and routers, the concept and functionality they provide remain important. They are still used in specific scenarios and environments where their simple and effective bridging capabilities are beneficial.

How secure is a network bridge?

The security of a network bridge depends on its implementation and the security measures in place within the network. Here are some factors to consider regarding the security of a network bridge:

Basic Security Features

  1. Traffic Filtering: Bridges can filter traffic based on MAC addresses, which can provide a basic level of security by preventing unauthorized devices from communicating with certain network segments.
  2. Spanning Tree Protocol (STP): Bridges typically use STP to prevent network loops, which can cause broadcast storms and potential network outages. Proper configuration of STP is essential for maintaining network stability and security.

Potential Security Risks

  1. Lack of Advanced Security Features: Unlike routers, which operate at Layer 3 and can implement more advanced security measures (e.g., firewalls, access control lists), bridges operate at Layer 2 and generally lack these capabilities.
  2. MAC Address Spoofing: An attacker could potentially spoof MAC addresses to gain unauthorized access to network segments. Bridges do not typically have mechanisms to prevent this type of attack.
  3. Broadcast Traffic: Bridges can potentially expose the network to broadcast storms if not properly configured or if a loop occurs that STP fails to mitigate.
  4. Vulnerability to ARP Spoofing: Since bridges operate at Layer 2, they are susceptible to ARP (Address Resolution Protocol) spoofing attacks, where an attacker sends fake ARP messages to associate their MAC address with the IP address of another device, leading to potential man-in-the-middle attacks.

Enhancing Security of a Network Bridge

  1. Implement Network Segmentation: Use VLANs (Virtual Local Area Networks) with switches to segment the network logically, providing better isolation and security control than physical bridges.
  2. Monitor and Manage MAC Addresses: Implement MAC address filtering and monitoring to detect and prevent MAC address spoofing.
  3. Use Secure Protocols: Implement secure network protocols and encryption to protect data transmitted across the network segments.
  4. Regular Updates and Patches: Ensure that any software-based bridges, such as those in virtual environments, are regularly updated and patched to protect against known vulnerabilities.
  5. Combine with Other Security Measures: Use bridges in conjunction with other security devices and measures, such as firewalls, intrusion detection/prevention systems (IDS/IPS), and network access control (NAC), to provide a comprehensive security posture.


While a network bridge can provide some basic level of security through traffic filtering and segmentation, it lacks the advanced security features found in routers and firewalls. To enhance the security of a network that includes bridges, it's essential to implement additional security measures, monitor the network for unusual activities, and ensure proper configuration and regular updates.