mac table full, switch behavior

[sarahr202]

Hi everybody.

Suppose we have a layer 2 switch whose mac table is full. We connect  a new  computer to switch.

Pc1 sends a frame to some computer on the network

How will switch react? Will it delete the oldest entry from mac table to make room for a new entry for pc1's mac?

Thanks and have a great day.

[Terry Cheema · Accepted solution]

When mac table is full, the switch fails over to broadcast mode and starts to broadcast the traffic to all ports in that VLAN. Mac address table overflow is a security vulnerability which attackers exploit by overflooding the CAM table to sniff the traffic. Port security was the answer to this.

In your case, With CAM table full, you introduced a new PC, all the traffic to the new PC will be broadcast to all the ports in that VLAN, till any of the entry times out and switch is able to store the entry for this host.

Hope that helps.

[Abzal · Accepted solution]

Hi,

When switch's CAM table full it starts working like a hub. MAC table entry ages out by default after 300 seconds.

Abzal