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Say I have the following network setup with about 100 clients connected:

1 GbE Ethernet/Internet -> GbE Router -> 1 GbE Ethernet -> GbE Switch -> Clients

Clients receive their IP:s from the router's DHCP server, but after that, if two clients want to communicate, can they do so directly over the switch or will their communication still have to pass through the router?

Will the single 1 GbE connection between the router and switch be a potential bottleneck if, say, Client A and B transfer large files on the local network while Client C, D and E are downloading files from the Internet?

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  • Possible duplicate of How does IPv4 Subnetting Work? Dec 12 '16 at 18:48
  • if two clients want to communicate, can they do so directly over the switch - Yes. Will the single 1 GbE connection between the router and switch be a potential bottleneck if, say, Client A and B transfer large files on the local network while Client C, D and E are downloading files from the Internet? - No.
    – joeqwerty
    Dec 12 '16 at 19:06
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All computers in an Ethernet network have a Layer 2 Address (MAC Address). If a computer (say 192.168.1.5) wants to communicate with another one (say 192.168.1.6) he/she sent an ARP request to all computers in the same broadcast domain asking them "who has 192.168.1.6?" Only the computer with this IP will respond with his MAC Address (Layer 2 address). Now the first computer (192.168.1.5) can send IP packets encapsulated in layer 2 frames.

Layer 2 frames are sent out from the network interface card to the switch. The switch (which is a Layer 2 device) holds an internal table that maps MAC Addresses to network ports. So the switch can "route" the traffic to the right direction without the help of a router.

So yes two clients can communicate directly over the switch and their communication will not be bottleneck to others.

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