Content Address Memory ( CAM )

By default, MAC Address are learned dynamically from incoming frames, when frames arrive on switch ports, the source MAC addresses, port of arrival and the VLAN are learned and recorded in the CAM table, along with time stamp. Switch never record those MAC addresses, which have not been participated in frame forwarding or stay receiving-only NIC addresses for more than 300 seconds .

 

Yes, by default, MAC addresses that have not been participated more than 300secs in frame forwarding, those are deleted. Entering the value 0 disables the MAC aging. If a VLAN is not specified, the aging specification applies to all. This benefit is provided for just because maintaining huge database that may cause a space issue in devices in a large infrastructure.

If a MAC address learned on one switch port has moved to a different port, the MAC address and time stamp are recorded for the most recent arrival port. Then, the previous entry is deleted. If a MAD address is found already present in the table for the correct arrival port, only it's time stamp is updated.

------------------- -------------------- ------------------- ------------------------- -------------------------------

You can change the default timer, if you have a smaller organization.

config# mac address-table aging-time 500seconds

If a MAC address is not learned by the port on the switch,  due to bug, you need to  have static CAM table entries by following command

config# mac address-table static XX.XX.XXX.XXX  vlan 1 interface gigethernet0/1

-----------------------------------------------------------------------------------------------------------------------

Note: you can use this command if there are already static entries applied, before you’re going to statistically configuring any mac address.

 

                                                                                                                                                                  Determining host  active on an interface

Checking the size of the cam table to verify how many hosts are using the network

CAM table entries can be cleared manually, if needed, by using the below command

switch#clear mac address-table dynamic [ address xx.xx.xx] or interface gigether0/1 or vlan 1

To determine mac address type(static or dynamic) configured on specific interface.

Some of the more use full commands

sh mac address-table interface 8/1 onuid 5

sh mac address-table vlan 56

sh mac address-table dynamic

sh mac address-table static