At university we are learning about ethernet switches and I got the following question:

What happens with the frames addressed to a machine x, if this machine is disconnected from the switch and then reconnected on a different link?

If a frame with an unknown address is received, I know the switch will send it to all the ports (frame flooding). Does the same thing happen here?



As @RonMaupin pointed out, this is handled via MAC address tables on the switch - a simple correlative system that compares incoming frames from devices (along with the source MAC of that frame, which is part of the frame data) with a record of all other connected devices.

For the most part the process of switching from one port to another along a bridge is effectively instantaneous. This is answered much more concisely here:



In addition to @SmallLoanOf1M's reference to RonMaupin's answer:

Disconnecting a NIC from a switch removes the NIC's MAC from the switches source address table. If in this state a frame is received by the switch it is flooded to all ports.

When there are several switches connected in a chain, the next switch further up will still associate the MAC with the port connecting both switches. So, moving the NIC to a different switch may cause some misdirected frames.

In practice, reconnecting the NIC to another port (potentially on a different switch) causes some traffic to be sent - the simplest solution for the host is to send a broadcast. This traffic takes care of updating the SATs on all related switches.

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