Technical data

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Chapter 12: Initial Switch Conﬁguration

CertPrs8/CCNA

Cisco Certiﬁed Network Associate Study Guide/Richard Deal/149728-5/Chapter 12

CERTIFICATION OBJECTIVE 12.04

Basic Switch Operation and Verification

This section focuses on the basic operations of a switch, such as learning MAC

addresses and basic verification commands.

MAC Address Table

You’ll recall that one of the three main functions of a switch is to learn which

devices—that is, MAC addresses—are associated with which interfaces or ports.

This information is stored in a port address, or content addressable memory (CAM),

table. The learning process was discussed in Chapter 4. You can view the CAM table

by using the show mac-address-table command. Here is an example of the

use of this command, based on the network shown in Figure 12-2:

Switch> show mac address-table

Mac Address Table

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

Vlan Mac Address Type Ports

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

All 0000.0000.0001 STATIC CPU

All 0000.0000.0002 STATIC CPU

1 0000.1111.AAAA DYNAMIC FA0/1

1 0000.1111.CCCC DYNAMIC FA0/2

1 0000.1111.BBBB DYNAMIC FA0/3

Total Mac Addresses for this criterion: 12

In this example, all the STATIC entries represent the switch itself. The last three

entries represent the MAC addresses learned from the first three interfaces of the

switch. By default, the 2960 can fit 8192 MAC addresses in its CAM table. To clear

dynamically learned entries from the CAM table, use the clear mac-address-

table command from Privilege EXEC mode.

You shouldn’t see a broadcast or multicast addresses in the port address table

since these are not seen as source addresses in frames and thus aren’t learned

by the switch.

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