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Bridging

Switches are layer-2 devices and forward incoming packets based on the MAC layer destination address. Furthermore, switches are self-learning and build their switching table automatically and dynamically adapt to network changes.

When a packet arrives on one of the interfaces, the switch behaves as follows:
  • The switch stores the source MAC address of the packet and the interface from which the packet arrived in the switching table (backward learning) and it adds an aging time.
  • Afterwards it looks for the packet's destination MAC address in the switching table and behaves as follows
    • Flooding: if the address is not found, a copy of the packet is sent over all the other interfaces
    • Filtering: if the destination address is on the same interface as the source, nothing is done by the switch
    • Forwarding: the switch forwards the packet to the interface found in the switching table.
The switch deletes an entry in the switching table, if no packets are received from this source after some time period (aging time). Thus it dynamically adapts to changes in the network.

Try the application by yourself. You are able to delete the switching tables and see how the switches behave with filled or empty tables!