I have a small LAN network.
Each table has a switch, and the laptops are connected to that switch.
There is a host which is using a large amount of the Internet bandwidth, and I would like to find out which one. I have that user's IP address (the guy who is using large amount of bandwidth), but there are many computers, so I cannot see to whom that IP address belongs.
Is there a way I can find the list of IP addresses connected to a switch (may be Unix command), so that I can visit each desk, run a command, and check all the active IP addresses (computers) connected to that switch, and based on that I can find out to which switch that specific IP address is connected?
Best Answer
Switches will know the MAC addresses, but not the IP addresses.
Switches are layer-2 devices, and the ethernet headers contain MAC addresses. A switch will create and maintain a MAC address table, which relates each MAC address with the port to which the device with that MAC address is connected.
IP is a layer-3 protocol, and IP addresses are in the packet headers, which are encapsulated inside the ethernet frame. A switch doesn't strip off the frame to look at the IP headers (router do that).
You need to relate the IP address to the MAC address. This is what ARP does. You can ARP with the IP address to discover the MAC address. Then, if your switch models have commands to do this, display the MAC address table of each switch to discover to which port the MAC address is connected. If the switches are all connected together, you may find the MAC address on a port which connects to a different switch, and you would then need to move to the switch on the connection and repeat the process until you find a host port.