Switching Tables (Part-4)

Managing the CAM Table

Each entry in the CAM table contains the following information:

• The MAC address
• The switch port the MAC address was learned on
• The VLAN of the switch port
• A time stamp, for the aging timer

To view the entire CAM table:

Switch# show mac address-table
vlan mac address type port
-------+---------------+---------+---------------------
9 000c.291e.96f0 dynamic GigabitEthernet1/1
9 000c.293c.7cac dynamic GigabitEthernet1/1
9 000c.2950.e3e9 dynamic GigabitEthernet1/1
9 000c.29ba.fe28 dynamic GigabitEthernet1/2
9 842b.2ba6.3a7d dynamic GigabitEthernet1/3
9 d067.e50b.1975 dynamic GigabitEthernet1/5
9 d067.e51e.e35a dynamic GigabitEthernet2/1
9 f04d.a2f6.d37b dynamic GigabitEthernet2/2

A single switch port can learn many addresses. In the above output, GigabitEthernet1/1 has multiple MAC addresses associated with it. This usually indicates this is an uplink to another switch.


To view the CAM table entries for a specific port or MAC address: 

Switch# show mac address-table interface GigabitEthernet 1/5
vlan mac address type port
-------+---------------+---------+---------------------
9 d067.e50b.1975 dynamic GigabitEthernet1/5


Switch# show mac address-table address f04d.a2f6.d37b
vlan mac address type port
-------+---------------+---------+---------------------
9 f04d.a2f6.d37b dynamic GigabitEthernet2/2

The output of a command can be filtered using the pipe command. For example, to search for any entry that contains 3a7d in the MAC address:

Switch# show mac address-table | include 3a7d
 vlan mac address type port
-------+---------------+---------+---------------------
 9 842b.2ba6.3a7d dynamic GigabitEthernet1/3

To specifically display only dynamic or static CAM entries:

Switch# show mac address-table dynamic
Switch# show mac address-table static


To view the total number of entries in the CAM table:

Switch# show mac address-table count
MAC Entries for all vlans:
Dynamic Unicast Address Count:                                     234
Static Unicast Address (User-defined) Count:                   0
Static Unicast Address (System-defined) Count:               6
Total Unicast MAC Addresses In Use:                             240
Total Unicast MAC Addresses Available:                         55000
Multicast MAC Address Count:                                       9
Total Multicast MAC Addresses Available:                       32768

The CAM aging timer can be changed from its default of 300, though this is needed only in rare circumstances:

Switch# config t
Switch(config)# mac address-table aging-time 360

To add a static entry into the CAM table:

Switch(config)# mac address-table static 0011.2233.4455 vlan 9 interface GigabitEthernet 2/7

To clear all dynamic entries in the CAM table:

Switch# clear mac address-table dynamic all

To clear a single entry in the CAM, either by MAC address or interface:

Switch# clear mac address-table dynamic address d067.e51e.e35a
Switch# clear mac address-table dynamic interface GigabitEthernet 2/1

Note: In Cisco IOS versions prior to 12.1, the syntax for all CAM table commands contained an additional hyphen between mac and address:

Switch# show mac-address-table

This additional hyphen is no longer required on modern versions of the IOS. Some IOS versions may support both syntaxes.