Network segmentation is the process of dividing the network to overcome problems and 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.[LIST][*]A
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
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.
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. Each interface represents its own broadcast domain if the router is configured to not forward broadcast packets.
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.
Routers perform the following functions that are not performed by bridges or switches.
[LIST][*]Route packets between separate networks[*]Modify packet size through fragmentation and combination[*]Route packets based on service address[/LIST]
Choose a router if you need to:
[LIST][*]Connect your network to a WAN, such as the Internet[*]Filter broadcast traffic to prevent broadcast storms[*]Connect two separate networks that use the same protocol[*]Improve performance in the event of a topology change (routers recover faster than bridges or switches)[*]Reduce the number of devices within a broadcast domain (effectively increasing the number of broadcast domains)[*]Enforce network security[*]Dynamically select the best route through an internetwork[*]Connect two networks of different architectures, for example Ethernet to Token Ring[/LIST]
Choose a switch if you need to:
[LIST][*]Provide guaranteed bandwidth between devices[*]Reduce collisions by decreasing the number of devices in a collision domain (effectively creating multiple collision domains)[*]Reduce the number of devices within a broadcast domain (creating multiple broadcast domains on a switch is done by using virtual LANs (VLANs))[*]Implement full-duplex communication[*]Connect two network segments or devices using the same protocol[*]Provide improved performance over a current bridged network[*]Switch traffic without the cost or administration involved with routers[/LIST]
Choose a bridge if you need to:
[LIST][*]Isolate data traffic to one network segment[*]Route traffic from one segment to another (with the same network ID)[*]Link unlike physical media (e.g. twisted pair and coaxial Ethernet) of the same architecture type[*]Link segments that use the same protocol[*]Create segments without the expense and administration of routers[/LIST]
Note: 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.
[LIST][*]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 or a switch with virtual LANs (VLANs) to filter broadcast messages, implement security, or connect different networks.[/LIST]