Network segment

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]

Ethernet

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.[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.

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.[3][4]

Layer 2 segment

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 the broadcast domain.

Traffic within a physical L2 segment can be separated into virtually distinct partitions by using VLANs. Each VLAN forms its own logical L2 segment.

Token ring

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

Token bus

All end stations connected to the same token bus are part of the same network 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.[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.

Other uses

References

  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.
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