Switch Learning Vs. Switch Forwarding: Answer
Today’s post wraps up this latest sample #CCENT exam question. Answer is below the fold.
First, the switch’s MAC table is empty.
Then, PC1 sends a frame, source MAC address 1111.1111.1111, arriving in port F0/1. As a result, the MAC table now lists PC1’s MAC off port F0/1. (We don’t care where this frame was forwarded, at least for this question).
Then, PC3 sends a frame, source of 3333.3333.3333, destination of PC2’s MAC. The frame arrives at the switch in port F0/3. So, the MAC table now lists PC3’s MAC off port F0/3.
The question asks: where does the switch forward this second frame, which has a destination address of 2222.2222.2222.
Per the MAC table at the instant the frame arrives, PC2’s MAC is not in the MAC table. So, the switch floods the frame.
In this case, flooding the frame in VLAN 1 means: forwarding out ports F0/1 and F0/2, but not out port F0/3, because the frame arrived in F0/3.