A physical portion of a local area network (LAN) that is separated from other portions by bridges or routers.
LANs are often “segmented” using bridges in order to improve network performance. Bridges are smart devices that build MAC-level routing tables that forward network traffic on the basis of the destination MAC address of each frame.
If the destination address of a frame is a machine in the local LAN segment, bridges attached to that segment will not allow the frame to pass; this reduces unneeded network traffic in other segments attached to the bridge.
Segmentation improves performance of Ethernet networks by reducing the number of stations in each segment of the LAN that must compete with each other for access to the network. Bridges are generally used for segmenting smaller LANs because they are cheaper and require no special configuration. You place a bridge between your department or workgroup hub and the main network backbone to improve traffic on your local segment.
Graphic L-2. LAN segment.