===== Sur Switch =====

  configure terminal
    interface fa0/20
      description CONNECTION TO ROUTER-ON-A-STICK
      switchport trunk encapsulation dot1q
      switchport mode trunk

===== Sur Routeur =====

  configure terminal
    interface fa0/0
      no ip address
      exit
    interface fa0/0.10
      description ROUTER INTERFACE FOR VOICE VLAN
      encapsulation dot1q 10
      ip address 172.16.1.1 255.255.255.0
      ip helper-address 172.16.2.5
      exit
    interface fa0/0.50
      description ROUTER INTERFACE FOR DATA VLAN
      encapsulation dot1q 50
      ip address 172.16.2.1 255.255.255.0