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Troubleshooting 802.1Q Troubleshooting 802.1Q
page 8-2 OmniSwitch Troubleshooting Guide September 2005
Troubleshooting 802.1Q
When troubleshooting an 802.1Q problem, it is important to not only investigate the 802.1Q feature and
configuration, but also the basic Ethernet connectivity between the problematic switches. Please refer to
Chapter 2, “Troubleshooting Switched Ethernet Connectivity,” of this document.
802.1Q Example
If there is no traffic passing at all across an 802.1Q link, verify basic Ethernet connectivity.
If there are particular VLANs that are not able to pass traffic, verify the configuration on both sides of the
link using the show vlan port CLI command. This will display the 802.1Q VLANs that are configured. It
will also display the default untagged VLAN. Confirm that these are configured correctly.
-> show vlan port 1/24
vlan type status
--------+---------+--------------
1 default forwarding
30 qtagged forwarding
40 qtagged forwarding
50 qtagged forwarding
Verify the ports are in forwarding as expected. Note which bridge mode the switch is running in (1 per
VLAN or 1 per switch) If spanning tree appears to not be working correctly, please see Chapter 4, “Trou-
bleshooting Spanning Tree,” of this document.
Note that different spanning tree protocols can be used on the same tagged port.
To verify which VLAN a specific flow is being classified into, use the show mac-address-table command
shown below:
-> show mac-address-table 5/24
Legend: Mac Address: * = address not valid
Vlan Mac Address Type Protocol Operation Interface
------+-------------------+--------------+-----------+------------+-----------
30 00:d0:95:88:67:ce learned 10806 bridging 5/24
50 00:d0:95:88:67:d0 learned 10806 bridging 5/24
Total number of Valid MAC addresses above = 2
OmniSwitch 7800
OmniSwitch 7800
Switch A Switch B