Verify that the trunking mode and encapsulation are configured correctly. Make certain that the native VLAN is the same on all of the 802.1q trunks that connect the Cisco switches to the non-Cisco 802.1q cloud. If multiple Cisco switches are connected to a non-Cisco 802.1q cloud, all of the connections must be through 802.1q trunks. Do not connect Cisco switches to a non-Cisco 802.1q cloud through ISL trunks or through access ports. If this is done, it causes the switch to place the ISL trunk port or access port into the spanning tree port inconsistent state and no traffic passes through the port. If the trunk does not pass specific VLAN traffic, the issue can potentially be that the VLAN has not been added in the database. Issue the vlan database privileged EXEC command in order to enter VLAN configuration mode. From this mode, it is possible to add, delete, and modify VLAN configurations for normal-range VLANs.

Note: The configurations of the VLAN IDs 1 to 1005 are saved in the VLAN database if the VLAN Trunking Protocol (VTP) is in the transparent or server modes. The extended-range VLAN configurations are not saved in the VLAN database.