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colemik
Asked: 2012-05-28 06:13:14 +0800 CST

Is this one network or two networks?

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I have this simple question and really don't know the answer. Does the drawing below show one network or two networks? This is a question about the definition of a network from the OSI / TCP/IP model point of view:

  • From one point of view, those are two L2 networks connected with a bridge.
  • From another point of view, this is one L3 network, that can have a common L3 address space (like 10.1.1.0).

PS

If this question is too dumb, please move it to Superuser.

enter image description here

networking bridge

2 Answers

  1. Best Answer

    It's one network. The bridge "bridges" the two physical segments into a single network. A bridge and a switch are (for all intents and purposes) the same thing in that they operate at Layer 2. A switch may also operate at Layer 3 (a L3 switch), but when it's performing L3 operations it's acting as a router not a switch.

    Broadcasts to FF:FF:FF:FF:FF:FF (255.255.255.255) are called limited broadcasts and are meant for every node on the same L2 network. An example of this type of broadcasting would be an ARP request.

    Broadcasts to the network/subnet broadcast address (192.168.1.255 on the 192.168.1.0/24 network for example) are called directed broadcasts and are meant for every node on the same L3 network. An example of this type of bradcasting would be a NetBIOS Name Query.

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  2. 1 network, there is a bridge between, which split the collision domains. The bridge splits one big network into two network segments. But it is still one network.

    The thing that is confusing is the word "network" it depends on how you define network. Network can be a set of connected computers, but the internet is also a network.

    In this case every pc is on the same broadcast domain so you can safely say that it is one network but it exists of network segments.

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