Network segment

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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.[1]


According to the defining IEEE 802.3 standards for Ethernet, a network segment is an electrical connection between networked devices using a shared medium.[2] 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.

With twisted-pair Ethernet, electrical segments can be joined together using repeaters or repeater hubs as can other varieties of Ethernet. This corresponds to the extent of a OSI layer 1 network and is equivalent to the collision domain.[3][4] The 5-4-3 rule applies to this collision domain.

Using switches or bridges, multiple layer 1 segments can be combined to a common layer 2 segment, i.e. all nodes can communicate with each other through MAC addressing or broadcasts. A layer 2 segment is equivalent to a broadcast domain.

Traffic within a layer-2 segment can be separated into virtually distinct partitions by using virtual LANs (VLANs). Each VLAN forms its own logical layer-2 segment.

Token ring[edit]

All end stations connected to the same Media Access Unit for token ring are part of the same network segment.[citation needed]

Token bus[edit]

All end stations connected to the same token bus are part of the same network segment.[citation needed]

Layer 3 segment[edit]

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.[5] 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.


  1. ^ "Network Segment Definition". 2 October 2005. Retrieved 2010-09-03. 
  2. ^ "1.4.318", 802.3-2008 Part 3: Carrier sense multiple access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications, IEEE, 26 December 2008, segment: The medium connection, including connectors, between Medium Dependent Interfaces (MDIs) in a CSMA/CD local area network. 
  3. ^ "Segment (Network)". Retrieved 2010-09-03. 
  4. ^ "Segment". Retrieved 2010-09-03. 
  5. ^ "What is a Network Segment?". Retrieved 2010-09-03.