When reading about layer 2 the word "link" is frequently used but strangely I'm struggling to find a formal definition of it. What is the precise definition of a link?

So in the image below, how many links are in this network and what makes that the case? Is it the physical cable between two devices, or can a link span multiple devices, or something else?

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2 Answers 2


There is no single precise definition for a "link".

A link can be a physical layer connection, two ports connected by a cable.

A link can also be understood as general connectivity by data link layer, ie. point-to-multipoint (as in "does the VLAN link over that trunk?" or with an aggregated link).

The TCP/IP model defines the link layer as the one below the network layer (=OSI layers 1 and 2). That model doesn't care what goes on in there.


Link is physical or Logical(Virtual) Connection which use to interconnect host/nodes(Devices). Link always refer connectivity. Link can span over multiple device. If you want to connection between America and Australia, You need to have Link. It will not be direct connection between two device. It is required to go through multiple devices.

Link Protocol is collection of standards that operate in LAN or WAN.(Between Adjacent Network nodes )

  • So would it be correct to say my laptop has a link with every accessible device in the internet as well as in my LAN? And following on from that, does my laptop have a link with transparent devices like switches that sit between it and other devices, even if it's not aware of it?
    – Isaac
    Apr 30, 2019 at 5:45
  • Just think you are flying from America to Australia,Your plane may go through Europe,Asia and many countries. Sometimes plane may land in few countries. You are not allow to visit those countries. But you can fly through those countries. You are flying to Australia not to Europe or other country. Same for Links as well. Hope you understand???
    – infra
    Apr 30, 2019 at 5:51
  • You have mixed link and connection, As nouns the difference between connection and link. is that connection is (uncountable) the act of connecting while link is a connection between places, persons, events, or things or link can be (obsolete) a torch, used to light dark streets. wikidiff.com/connection/link
    – infra
    Apr 30, 2019 at 5:56

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