Cisco Switch: 802.1q Trunk to Router (a.k.a. Router-on-a-Stick)

Posted November 17, 2006 by Al Banks in Cisco switch

You can connect a Cisco switch and router via 802.1q trunking. This configuration is known as a router-on-a-stick.


First, let us start with the switch. VLAN 1 exists by default, so we will add a couple of other VLANs:

vlan 100
name data
state active

vlan 200
name data
state active

Now, we will configure the switchport to connect to the router:
interface fastethernet 1/0/1
switchport trunk encapsulation dot1q
switchport mode trunk

Now, we will move to the router.

interface fastethernet 0/0
no ip address

interface fastethernet 0/0.1
encapsulation dot1q 1 native

interface fastethernet 0/0.100
encapsulation dot1q 100
ip address 192.168.100.1 255.255.255.0

interface fastethernet 0/0.200
encapsulation dot1q 200
ip address 192.168.200.1 255.255.255.0

At this point, workstations on VLAN 100 should be able to ping the 192.168.100.1 address, and workstations on VLAN 200 should be able to ping the 192.168.200.1 address.

If, for some reason, the native VLAN on the switchport is something other than one (1), change the encapsulation statement on the router, or the trunk may not form.

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