interface FastEthernet0/1 switchport access vlan 100 switchport mode dot1q-tunnel l2protocol-tunnel cdp no cdp enable
The access VLAN which is here called Tunnel-Tag, must exist in the transit path.
In a scenario where EtherChannel is implemented between two 802.1q customers and there are more than 1 switch in the transit path, and each CE switch has for example 3 different links to CE node, each PE-to-CE should be assigned to a different VLAN.
Also, the transit path should be in form of TRUNK links, and informed of the Tunnel-Tag VLANs.