Infrastructure Technology  «Prev  Next»

Lesson 5 Switches, bridges, and routers
Objective Describe the functions of switches, bridges, and routers.

Reducing Collisions in Local Area Networks (LANs) Using Switches, Bridges, and Routers

Local Area Networks (LANs) have historically been susceptible to collisions, particularly in environments utilizing shared communication mediums such as Ethernet's original half-duplex operating mode. Collisions can degrade network performance and limit throughput. As LANs evolved, several networking devices, including switches, bridges, and routers, were introduced to mitigate collision-related challenges. This technical documentation delves into the mechanisms by which these devices reduce or eliminate collisions in LANs.
  1. Switches: Switches play a pivotal role in minimizing collisions within Ethernet networks.
    • Dedicated Collision Domains: Unlike hubs, which broadcast data to all connected devices, switches establish dedicated collision domains for each connected device. This ensures that data frames sent from a device to the switch don't collide with frames from other devices.
    • Full-Duplex Operation: Modern switches support full-duplex mode, allowing devices to transmit and receive data simultaneously without the risk of collisions. This contrasts with half-duplex mode, where devices cannot send and receive at the same time, making them prone to collisions.
  2. Bridges: Bridges are network devices that connect multiple network segments, acting as a filter to reduce network traffic and, consequently, collisions.
    • Segmentation: By dividing a LAN into separate collision domains, bridges reduce the number of devices that compete for bandwidth on each segment. This segmentation decreases the likelihood of collisions.
    • Frame Filtering: Bridges possess the intelligence to determine if a data frame should be forwarded or filtered. By examining the MAC address of a frame, a bridge can decide whether the frame should cross over to another segment, thus reducing unnecessary traffic and potential collisions.
  3. Routers: Routers are advanced networking devices that route data packets between different networks. Their introduction to a LAN environment offers the following collision-reducing benefits:
    • Separate Broadcast Domains: Routers inherently separate broadcast domains. This means that broadcast traffic, a common source of collisions in large networks, is confined to its originating network, preventing it from flooding other connected networks.
    • Layer 3 Functionality: Operating at the Network layer (Layer 3) of the OSI model, routers make forwarding decisions based on IP addresses rather than MAC addresses. This ensures that data is directed only to its intended destination network, eliminating unnecessary traffic within individual LAN segments.
    • Path Selection: Routers can determine the best path for data packets to reach their destination. By optimizing these paths, routers can distribute network traffic more evenly, preventing potential congestion points that can lead to collisions.

The integration of switches, bridges, and routers in a LAN environment represents a strategic approach to collision mitigation. Through the intelligent segregation of collision and broadcast domains, along with advanced data filtering and path selection, these devices collectively enhance network efficiency, optimize bandwidth utilization, and ensure a more stable and collision-resistant LAN infrastructure. As network demands continue to escalate, the role of these devices in preventing collisions remains paramount for maintaining optimal network performance.

What are Switches, Bridges, and Routers?

Switches, bridges, and routers are products that interconnect LANs, WANs, and networks of different types. They orchestrate the entire networking system, and therefore are critically important to the overall performance of your solution. Switches, bridges, and routers all interconnect the networks that will make up your solution, so it's important to understand the differences among them.


A switch is a network device that filters and forwards data packets between LAN segments. In so doing, they compensate for speed differences between networks. Switches operate at the data link layer (layer 2) of the OSI Reference Model and therefore support any packet protocol. LANs that use switches to join segments are called switched LANs.[1] This graphic illustrates a switch.

This illustrates a switch.
This diagram illustrates a switch between two local area networks.


A bridge is a device that connects two LANs or two segments of the same LAN. Like switches, they too compensate for network speed differences.
With bridges, the two LANs being connected can be similar or dissimilar. Like switches, bridges operate at the data link layer (layer 2) of the OSI Reference Model and therefore are protocol-independent. They simply forward data packets without analyzing and re-routing messages. This graphic illustrates a bridges.

This illustrates a bridge.
A network bridge is a computer networking device that creates a single aggregate network from multiple communication networks or network segments.


A router is a device that connects any number of LANs, as shown here.
This shows a router.
A router is a networking device that forwards data packets between computer networks. Routers perform the traffic directing functions on the Internet.

Routers use headers and a forwarding table to determine where packets should go. In addition, in contrast to bridges, they also use specific routing protocols to communicate with each other and configure the best route between any two hosts.
In general, routers perform very little data filtering and they do not care about the type of data they handle. The table below clarifies the defining characteristics of switches, bridges, and routers.

Characteristic Switches Bridges Routers
How they process information Filter, forward, and convert packet information Filter, forward, and convert packet information Forward packet information and perform address directory mapping and resolution.
Their benefit to networking Compensate for speed differences between different networks Compensate for speed differences between different networks Balance and filter traffic within LAN groups for security purposes and policy mangement
Where they are based Hardware Software Hardware
Where they work Data-link layer (OSI 2 layer) Data-link layer (OSI 2 layer) Networking layer (OSI layer 3)

[1]Switched LANs: LANs that use switches to join segments.

Ad Advanced Digital Architectures