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Here’s the MAC address of R1, learned dynamically. Total Mac Addresses for this criterion: 1 Let’s take a look at the MAC address table: SW1# show mac address-table dynamic vlan 1 Success rate is 80 percent (4/5), round-trip min/avg/max = 1/2/4 ms Sending 5, 100-byte ICMP Echos to 192.168.12.2, timeout is 2 seconds: We’ll do a quick ping to generate some traffic so SW1 can learn about the mac address of R1’s FastEthernet 0/0 interface: R1# ping 192.168.12.2

Here’s the configuration: R1(config)# interface fastEthernet 0/0 A router to generate some traffic and a switch to look at (and configure) the MAC address table. To demonstrate this we only require two devices. You can either specify the interface where the MAC address is located or tell the switch to drop the traffic. A really simple method to deal with this issue is to manually configure entries in the MAC address table, a static entry will always overrule dynamic entries.

This process is vulnerable to layer 2 MAC address spoofing attacks where an attacker spoofs a certain MAC address to change entries in the MAC address table. Normally your switch will automatically learn MAC addresses and fill its MAC address table (CAM table) by looking at the source MAC address of incoming frames and flooding frames if it doesn’t know where to forward the frame.