Flooding of a switch

[chandra_rc16]

Hi All,

Here is my topology. I'm analysing the MAC address learning process of a switch.

Assume that the switch has MAC entries of WS2 and WS4 only. So when i ping WS1 from WS2, since the switch doen't have the WS1 MAC entry it will flood the frame...  but i thought it will flood only on Fa0/1 port and Fa0/3 port but it flooded the frame to Fa0/4 port also, which it should not because already it has the MAC entry of WS4 on Fa0/4. Can someone please explain, why this happened ?

Will the switch assume that device on Fa0/4 might have change and done this flooding on Fa0/4 also or else what is the reason?

Regards,

Chandu

[Jon Marshall · Accepted solution]

The switch has no way of knowing what is reachable via fa0/4. It could just be a PC as in your example but it could be another switch with multiple devices connected in which case there would be multiple mac addresses associated with fa0/4.

Because the switch has no way of knowing what is on the end of the link from fa0/4 it has to flood the frame. So the switch will flood the frame to all ports within the same vlan except the port it was received on.

Jon

[chandra_rc16]

Thanks a lot, Jon. Well explained.

Regards,
Chandu