Troubleshooting guide

12-7
ATM and Layer 3 Switch Router Troubleshooting Guide
OL-1969-01
Chapter 12 Troubleshooting Layer 2 Interfaces
Troubleshooting Layer 2 Switching
To troubleshoot Layer 2 switching, perform the following steps:
Step 1 Use the show spanning-tree command to display bridge group information as shown in Figure 12-4.
Switch# show spanning-tree 1
Bridge group 1 is executing the IEEE compatible Spanning Tree protocol
.
(Information Deleted)
.
Port 43 (FastEthernet12/0/1) of Bridge group 1 is forwarding
.
(Information Deleted)
.
Port 58 (GigabitEthernet11/0/1.1 ISL) of Bridge group 1 is forwarding
Step 2 Find the entries in the show spanning-tree command output for the interfaces in question and check the
Port fields to confirm the ports at Fast Ethernet12/0/1 and Gigabit Ethernet 11/0/1.1 ISL are forwarding.
Step 3 Use the show bridge command to display bridge group information.
Switch# show bridge 1
.
(Information Deleted)
.
Bridge Group 1:
Address Action Interface
0010.e3aa.aaaa forward Fa12/0/1
0090.21bb.bbbb forward Gi11/0/1.1
Find the entries for those interfaces in the show bridge command output. Note the Address fields to see
that the MAC addresses being forwarded to the Fast Ethernet12/0/1 and Gigabit Ethernet 11/0/1.1 ISL
connections are in the bridge table. These addresses are used in the following step.
Step 4 Use the show epc mac interface FastEthernet interface command with the MAC address parameter.
Add the MAC address being forwarded to interface FastEthernet 12/0/1.
Switch# show epc mac interface FastEthernet 12/0/1 0010.e3aa.aaaa
MACaddr:0010.e3aa.aaaa IF Number:43 MAC Local
Note the IF Number field; in this example, the number is “43.” You will need this number in the
following command.
Step 5 Use the show epc mac interface GigabitEthernet interface command with the MAC address parameter.
Add the MAC address being forwarded to interface GigabitEthernet 11/0/1.1 ISL.
Switch# show epc mac interface FastEthernet 12/0/1 0090.21bb.bbbb
MACaddr:0090.21bb.bbbb IF Number:58
Note the IF Number field; in this example, the number is “58.” You will need this number in the
following command.