Segmentation Facts
LAN segmentation is the process of dividing the network to overcome problems such as excessive collisions, broadcast traffic, or heavy network traffic. By segmenting a LAN, you can increase network performance, maximize bandwidth, and reduce congestion.
As you segment the network, you will need to consider the collision and broadcast domains on the network.
- A collision domain is any network or subnetwork where devices share the same transmission medium and where packets can collide. Collisions naturally increase as the number of devices in a collision domain increase.
- A broadcast domain is any network or subnetwork where computers can receive frame-level broadcasts from their neighbors. As you add devices to a network segment, the amount of broadcast traffic on a segment also increases. Note: A special condition called a broadcast storm happens when broadcast traffic is sent, regenerated, and responded to. In this condition, the amount of broadcast traffic consumes network bandwidth and prevents normal communications. Faulty devices or improper configuration conditions can lead to a broadcast storm.
Segmentation may increase the number of both the collision and broadcast domains. Membership within collision or broadcast domains differs depending on the connection device used.
Device | Collision Domain | Broadcast Domain |
Hub | All devices connected to the hub are in the same collision domain | All devices are in the same broadcast domain |
Bridge or Switch | All devices connected to a single port are in the same collision domain (each port is its own collision domain) | All devices connected to the bridge or the switch are in the same broadcast domain |
Router | All devices connected to a single interface are in the same collision domain | All devices accessible through an interface (network) are in the same broadcast domain |
In considering a network expansion solution, it is important to identify the connectivity problems you need to resolve, and then identify the device that is best suited for that situation. The main differences between routers, switches, and bridges is the range of services each performs and the OSI layer at which they operate.
Device | Characteristics |
Router | Routers perform the following functions that are not performed by bridges or switches.
Choose a router if you need to:
|
Switch | Choose a switch if you need to:
|
Bridge | Choose a bridge if you need to:
In most cases where you might use a bridge, choose a switch instead. |
In general, follow these guidelines to make decisions about the appropriate connectivity device.
- Use a bridge to segment the network (divide network traffic) and to provide fault tolerance.
- Use a switch to reduce collisions and offer guaranteed bandwidth between devices.
- Use a router to filter broadcast messages, implement security, or connect between different networks.
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