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I would want to buy a ethernet switch. But I have a question (maybe a noob's question...) that I can't find any answer on the forums... And I hope you will be able to answer. So if I buy an ethernet switch, connect it to network and connect 3pc to it (for instance), how many Mac adresses will be shown in output? For example, if the switch is connected to a router, how many Mac adresses will the router see? Just one, the switch 's Mac? Or each Mac adresses of any pc connected to the switch?

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  • In what way is answering this question relevant to buying an Ethernet switch? Maybe if you explained what you were trying to do and why you need to know "how many MAC addresses" we could provide a better answer. – YLearn Sep 4 '15 at 7:55
  • I'm behind a proxy which allow only 4 Mac adresses. I was wondering of by buying a switch I would be able to have more than 4 Mac adresses. Indeed proxy filters mac adresses. So we must declare our Mac adresses, 4 maximum. Declared Mac adresses are added by a network administrator to Whitelist. But I have more than 4 Mac adresses and I would want to connect all my devices. So my question is – frankee Sep 4 '15 at 11:58
  • Based on your comment, you need a layer-3 device (router, layer-3 switch, etc.) between your switch and the proxy. This question is a little bit on the edge since you may be trying to circumvent the network policies of a network over which you have no control. – Ron Maupin Sep 4 '15 at 14:58
  • @RonMaupin A Layer-2 bridge device capable of MAC NAT (e.g. every Linux machine) would also do this trick. – Alex Stragies Apr 1 '17 at 12:11
  • You are confusing network layers. NAT happens at layer-3 or layer-4, but ethernet is at layer-2. Ethernet switches are transparent devices. They do not modify frames, except to add a VLAN tag on a trunk. What you want doesn't exist. – Ron Maupin Apr 1 '17 at 12:32
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A switch learns the MAC addresses connected to each one of its ports. For example:

  • Port 1 - Connected to PC -Learns 1 MAC on this port.

  • Port 2 - Connected to router - Learns 1 MAC on this port.

  • Port 3 - Connected to hub - learns as many MACs as PCs are connected to the hub.

The Switching table of the switch will be something like this:

     MAC              PORT
0f-aa-34-56            1
0a-17-40-12            2
09-11-11-11            3
05-65-23-59            3
0f-0a-71-62            3

The router on Port 2 will be able to communicate with any other PC (the PC on port 1 or any other one on Port 3) and works transparently. A switch can't modify mask or modify a MAC address.

The switch isolates ethernet collisions, so if a collsion happens on the hub , the router and the PC on Port 1 won't notice it.

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  • OK so the router where the switch is connected will see all these Mac adresses? (switch connected to router) – frankee Sep 4 '15 at 12:02
  • @frankee Yes. If you want to hide MAC adresses, use a router. The router removes the source MAC and replace it with its own MAC. – jcbermu Sep 4 '15 at 12:05
  • Oook ! So for doing what I would want,I rather need a router. But the switch won't remove source Mac and replace them with its own, will it? – frankee Sep 4 '15 at 12:09
  • @frankee A switch won't remove source Mac and replace them with its own. A router does that when is communicating different IP networks. – jcbermu Sep 4 '15 at 12:59
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In your question. If a router is connected directly with a switch, must know all the addresses that for some point, communicate with him. In th other hand, the switch always must show you 2 mac address per port, the port MAC, and the MAC of the NIC connected to him. This one, will be stored, by default, 300 seconds.

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