LANsegment

LAN segment is a portion of a local area network that is treated as a single data-link layer segment for forwarding decisions. In traditional Ethernet networks that use a shared medium such as coax or hubs, a LAN segment corresponds to the physical section of cable on which devices contend for access and thus forms a single collision domain. When two devices transmit simultaneously on such a segment, a collision may occur, and protocols like CSMA/CD coordinate retransmission.

In modern switched Ethernet, switches break up collision domains. Each switch port generally represents a separate collision domain, so devices connected to different ports do not collide with each other. A LAN segment in this context is often the set of devices connected to a single port or, more commonly, the network portion defined by a VLAN that ties together multiple switch ports into one logical segment. Broadcast behavior, however, is controlled by routers and VLANs rather than by switches alone.

Routers separate broadcast domains, while switches do not by default. VLANs enable administrators to partition a single physical LAN into multiple broadcast domains at Layer 2 for performance and security. Within a VLAN, all devices receive broadcast frames sent to that VLAN, regardless of their physical location, unless segmented by routers or Layer 3 devices. When planning LAN segments, designers consider factors such as traffic patterns, collision domain management, and broadcast traffic.

See also: LAN, Ethernet, collision domain, broadcast domain, VLAN.