6500 Catos L2 L3, MAC problem

Unanswered Question
Sep 23rd, 2008

Hi everybody

We have two 6500 Catos connected through an L2 ethernchannel. This couple of 6500 are doing L2 and L3 Task. In one 6500 are connected one router trying to communicate with another router connected to the other 6500. We are looking that the mac address of the second router disappear sometimes and it causes that all the vlan sees a lot of traffic because of the broadcast of the ARP. Could sombody help me how can I solve this rare behavior? Tks

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
Giuseppe Larosa Tue, 09/23/2008 - 23:14

Hello Pedro,

with default settings the MAC address stays in the CAM for 300 seconds.

the default age time in the router ARP table is four hours.

So it is more likely that the broadcast you see is the flooding of unknown unicast when the entry in the CAM is aged out.

What can be done:

a) add a routing protocol between R1 and R2 so that every 10/30 seconds a frame with source MAC R2:f0/0 is heard by the switches and the entry is never aged out


b) you could add a static entry stating that R2:f0/0 MAC is out interface m/z on the switch L2 supervisor

Verify with

sh cam count

that the CAM table is not overloaded by a misbeaving host (mac address attack)

Hope to help


p.diaz Wed, 09/24/2008 - 05:21

Thanks a lot Guiseppe for your ideas. let me try.


This Discussion