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This seems like a simple question, but I can't find a definitive answer for it. I have four devices connected to a Gigabit switch as in this diagram:

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Can I get the full GBit bandwidth from A-B simultaneously as C-D are maxing out their link? Or, in general, do they "share" the bandwidth through the switch?

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    Switches have a maximum throughput for the switch. This is how fast the switch can process the data passing through it. This number is dependant on the switch make/model specifically, which you have not included in your question. Having said that, what makes you think it wouldn't work? What problem are you encountering exactly? – Ƭᴇcʜιᴇ007 Feb 3 '15 at 19:04
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    @Techie007, I specifically didn't include the model of my switch, as I'd like to know the generic "theoretical" answer. That said, I don't see a maximum throughput rating in its spec sheet. It does list "Filtering/Forwarding Rate: 1000Mbps/1,488,000pps", but its unclear to me what that means. – Sam Feb 3 '15 at 19:35
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    "This seems like a simple question..." -- It's not. There are many performance factors, including switch implementations, i.e. store-and-forward versus cut-through. dlink.com/uk/en/support/faq/switches/layer-3-gigabit/dgs-series/… – sawdust Feb 3 '15 at 20:25
  • The simple answer is that you can get all of the computers talking at gigabit speeds without any slowdowns IF the switch is capable. – MonkeyZeus Feb 3 '15 at 20:52
  • @sawdust, I get that there are many factors (hardware, OS/software, settings, etc) that go into what is actually achievable in the real world. I just need to know if the "gigabit" in "gigabit Ethernet switch" generally refers to total capacity, or per-node. It sounds like the answer is the latter. – Sam Feb 3 '15 at 21:57
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With a well-designed Ethernet switch, it's possible to get the full port speed into each port and the full port speed out each port, all simultaneously (switch ports are full-duplex).

A switch designed to guarantee it can do this will be marketed has having an aggregate throughput of:

2 * (#-of-ports) * (speed-per-port)

This is sort of double-counting because the data going out any given port must have come in some other port, but this double-counting has become a de facto industry standard marketing practice.

So in your example of a 4-port Gigabit Ethernet switch, it would be marketed as having 8Gbps of bandwidth.

Unfortunately, it wouldn't surprise me if most 4-8 port GigE switches are cheap consumer crap that can't do that and thus wouldn't be marketed as such.

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