A network segment is a portion of a computer network. The nature and extent of a segment depends on the nature of the network and the device or devices used to interconnect end stations.
Electrically connected segment
According to the defining IEEE standards for Ethernet, a network segment is an electrical connection between networked devices using a shared medium.
In the original 10BASE5 and 10BASE2 Ethernet varieties, a segment would therefore correspond to a single coax cable and any devices tapped into it. At this point in the evolution of Ethernet, multiple network segments could be connected with repeaters (in accordance with the 5-4-3 rule for 10 Mbit Ethernet) to form a larger collision domain.
Layer 1 segment
With twisted-pair Ethernet, electrical segments can be joined together using repeaters or repeating hubs. This corresponds to the extent of a OSI Layer 1 network and is equivalent to the collision domain.
Layer 2 segment
Using switches or bridges, multiple layer 1 segments can be combined to a common layer 2 segment, ie. all nodes can communicate with each other through MAC addressing or broadcasts. A layer 2 segment is equivalent to the broadcast domain.
Traffic within an physical L2 segment can be separated into virtually distinct partitions by using VLANs. Each VLAN forms its own logical L2 segment.
Layer 3 segment
A layer 3 segment in an IP network is usually called a subnetwork, formed by all nodes sharing the same network prefix as defined by the network mask. They can communicate directly on the layer 2 level. Most often, an L3 subnet corresponds with the underlying layer 2 segment but it's also possible to run multiple subnets in parallel within a single L2 segment.
Transmitting communication between layer 3 subnets requires a router.
- a language space within the Internet, such as Runet or Kaznet.