show mac address-table
I’m sure you remember being shown the show mac address-table command earlier in the
chapter. Using it displays the forward filter table also called a content addressable memory
(CAM) table. Here’s the output from the S1 switch:
S1#sh mac address-table
Mac Address Table
-------------------------------------------
Vlan Mac Address Type Ports
---- ----------- -------- -----
All 0100.0ccc.cccc STATIC CPU
All ffff.ffff.ffff STATIC CPU
[output cut]
1 0002.1762.b235 DYNAMIC Po1
1 0009.b79f.c080 DYNAMIC Po1
1 000d.29bd.4b87 DYNAMIC Po1
1 000d.29bd.4b88 DYNAMIC Po1
1 0016.4662.52b4 DYNAMIC Fa0/4
1 0016.4677.5eab DYNAMIC Po1
1 001a.2f52.49d8 DYNAMIC Po1
1 001a.2fe7.4170 DYNAMIC Fa0/8
1 001a.e2ce.ff40 DYNAMIC Po1
1 0050.0f02.642a DYNAMIC Fa0/3
Total Mac Addresses for this criterion: 31
S1#
The switches use what are called base MAC addresses that are assigned to the CPU, and the
2960s use 20. From the previous output, you can see that I have five MAC addresses dynamically
assigned to EtherChannel port 1. Ports Fa0/3, Port8, and Fa0/4 have only one MAC
address assigned, and all ports are assigned to VLAN 1. This code has been described many
times in this chapter.
S2#sh mac address-table
Mac Address Table
-------------------------------------------
Vlan Mac Address Type Ports
---- ----------- -------- -----
All 0008.205a.85c0 STATIC CPU
All 0100.0ccc.cccc STATIC CPU
All 0100.0ccc.cccd STATIC CPU
All 0100.0cdd.dddd STATIC CPU
[output cut]
1 0002.1762.b235 DYNAMIC Fa0/3
1 000d.29bd.4b80 DYNAMIC Fa0/1
1 000d.29bd.4b85 DYNAMIC Fa0/1
1 0016.4662.52b4 DYNAMIC Fa0/1
1 0016.4677.5eab DYNAMIC Fa0/4
1 001b.2b55.7540 DYNAMIC Fa0/1
Total Mac Addresses for this criterion: 26
S2#
You can see in the previous output that I have four MAC addresses assigned to Fa0/1. And
of course, you can also see that you have one connection for each host on ports 3 and 4. But
where’s port 2? Since port 2 is a redundant link, STP placed fa0/2 into blocking mode.