“Router on a Stick”

So far we have been exposed to "Router on a Stick" configuration twice. One is the second video in CCENT Virtual LANs, another time is in CCNA VLANs and Trunking.

Router-on-a-stick is a term frequently used to describe a setup up that consists of a router and switch connected using one Ethernet link configured as an 802.1q trunk link.

router on a stick

As the picture shows, a router is used to allow inter-VLAN communication. There is only a single cable connecting the switch and the router, so the router is sitting on a stick (instead of 2 sticks).

the switch config involves:

• configuring the VLANs 
• configure a port as trunk mode in order to connect to router

Switch(config)#vlan 10
Switch(config-vlan)#exit
Switch(config)#vlan 20
Switch(config-vlan)#exit
Switch(config)#vlan 30
Switch(config-vlan)#exit
Switch(config)#interface FastEthernet0/4
Switch(config-if)#switchport trunk encapsulation dot1q
Switch(config-if)#switchport mode trunk

the router config include:

• select a physical port as the port connecting to switch.
• configure a sub interface for each VLAN on the switch. 

Router(config)#interface gigabiteEthernet0/0
Router(config-if)#no ip address
Router(config-if)#interface gigabiteEthernet0/0.10
Router(config-subif)#encapsulation dot1Q 10
Router(config-subif)#ip add 192.168.5.1 255.255.255.0
Router(config-subif)#interface gigabiteEthernet0/0.20
Router(config-subif)#encapsulation dot1Q 20
Router(config-subif)#ip add 192.168.10.1 255.255.255.0
Router(config-subif)#interface gigabiteEthernet0/0.30
Router(config-subif)#encapsulation dot1Q 30
Router(config-subif)#ip add 192.168.15.1 255.255.255.0

[ICND1 and ICND2 break down]