here is an example to explain my incomprehension: PING: PC1 -----> SWITCH -------> PC2.

i know that when a PC1 send frame to switch, the switch will add the mac address to his mac address table, then it will diffuse the frame to all the PCs including PC2. PC2 respond to switch (because the message is refer to him) and the switch the mac address of PC2 to his mac address table.

PC1 -----> SWITCH -------> PC3.

now, when PC1 send frame to Switch. do switch diffuse the frame to all the PCs including PC2, OR it diffuse to all the PCs without PC2 since switch knows the mac address of PC2.

thank you.

1 Answer 1


Hi and welcome to Network Engineering!

"Diffuse" is the wrong word to use here. Switches operate this way:

If the destination MAC is in the MAC table, the switch forwards the frame only to the port listed in the table.

If the MAC is not in the table, the switch floods (not diffuse) the frame out all ports (except the one it was received on).

  • thanks you sir, this is a reasonable answer. but i m confusing because the switch in packet tracer dont work like that
    – laoui adel
    Oct 5, 2018 at 13:20
  • What is packet tracer doing? Sometimes, simulations don't work that same way as real devices.
    – Ron Trunk
    Oct 5, 2018 at 13:23

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