Segment (network)
A network segment is part of a larger, coherent network that is virtually and / or physically separated from the rest of the network.
There are various reasons for dividing a network into several network segments: In larger networks this is useful for distributing the load of the broadcasts . In the case of interfaces between Local Area Network (LAN) and Wide Area Network (WAN), for example the Internet , separation makes sense for security reasons.
The term segment is used in a computer network at different OSI levels for different delimitations.
- On OSI layer 1, it denotes the common physical medium to which computers are connected and is synonymous with collision domain .
- On OSI layer 2 in bridges , the networks at the two interfaces are also referred to as segments. Similarly, ports on the switch that lead to multiple MAC addresses are referred to as segment ports.
- On OSI layer 3 for IP, the term segment is synonymous with an IP subnet or with a broadcast domain.
Segments, Layer-1, Collision Domain
Within a common segment on OSI Layer 1, several computers are connected in a common collision domain analogous to physical bus topologies . With Ethernet, this type of connection is via coaxial cables or hubs .
A segment can only connect exactly two participants ( point-to-point ). This form is used for wiring using twisted pair cables or fiber optic cables . A segment with a point-to-point connection is often referred to as a link segment.
Repeaters or hubs can be used within a segment. Different layer 1 segments, however, are connected to each other via coupling elements such as bridges, switches or routers to form layer 2 or layer 3 segments.
Segments, Layer-2, Broadcast Domain, Segment Ports
Bridges and switches combine the connected networks into a layer 2 segment, which in turn can consist of any number of collision domains. Similarly, ports on the switch that lead to multiple MAC addresses are referred to as segment ports. Since Layer 2 broadcasts are transmitted to all ports in the same L2 segment, the term broadcast domain is also used here.
Segments, layer 3, IP networks and subnets
On Layer 3, entire TCP / IP networks or subnets are sometimes referred to as segments. In other words, stations with the same broadcast domain form a common subnet, which is normally congruent with an L2 segment. Different segments have to be linked via routers.