Resolution
This example shows how to configure the FastEthernet port on an 1841 router as a trunking interface. The Cisco 1841 router has two onboard FastEthernet autosensing interfaces that support 10- or 100-Mbps connections.
The sub interface becomes fa 0/x.. For instance, fa 0/1.2 represents the sub-interface for VLAN 2. In addition, it is necessary to define the encapsulation as encapsulation dot1q vlan-id.
Hostname(config)#interface FastEthernet0/1
Hostname(config-if)#no ip address
Hostname(config-if)#no shutdown
Hostname(config)#interface FastEthernet0/1.1
Hostname(config-if)#encapsulation dot1Q 1 native
Hostname(config-if)#ip address x.x.y.y < subnet mask >
Hostname(config-if)#interface FastEthernet0/1.2
Hostname(config-if)#encapsulation dot1Q 2
Hostname(config-if)#ip address x.x.y.y < subnet mask >
Note: There is no way to setup the 1841 router to negotiate the trunk.
