Frame Forwarding

[kbullard00]

     I don't understand why a frame is forwarded out ports that the switch has already assigned

MAC addresses to.

Plz see diagram.

[Dale Miller · Accepted solution]

This is unicast flooding. The packet is flooded in the VLAN since the destination mac is not in the mac table on sw2. MAC learning takes place packet is received, the switch records the src mac-address and addes it to the MAC table. By defaut mac aging is configured for 5 minutes and the entry will be updated as long as it keeps receiving packets.

Per your diagram this is expected behavior.

Regards,
Dale

[Peter Paluch]

Hello,

Dale has explained this very well. Let me just add one remark: you are obviously assuming that just because there are already some MAC addresses learned on a port, no other frames will be forwarded out through it. This is a wrong assumption; a switch can never be sure if it already knows MAC addresses of all its stations - some may not have sent any frame so far, and some may be silent for so long a period that their MAC addresses have been flushed. Therefore, regardless of any learned MAC addresses on ports, a frame with an unknown destination will always be flooded out all remaining ports (in the same VLAN).

Best regards,

Peter

[kbullard00]

Great. Those last two sentences really made the difference. thx