Hi Miguel De Santiago My name is Johnnatan Rodriguez, your information about the vlan's is correct, now I'm goint to explain to you, why does the router need subinterfaces? Subinterfaces: we need it when we have more vlans than physical links As you said, we have  setup a trunking port between the switch and router, then configure the configure the interface and sub interfaces in your router: Switch(config)#interface fa0/2 Switch(config-if)#switchport mode trunk Router(config)#interface fa0/1 Router(config-if)#no shutdown Router(config)#interface fa0/1.1 Router(config-subif)#encapsulation dot1q 1 Router(config-subif)#ip address 192.168.10.1 255.255.255.0 Router(config)#interface fa0/1.2 Router(config-subif)#encapsulation dot1q 15 Router(config-subif)#ip address 192.168.15.1 255.255.255.0 Router(config)#interface fa0/1.3 Router(config-subif)#encapsulation dot1q 35 Router(config-subif)#ip address 192.168.20.1 255.255.255.0 We configure sub interfaces because we have 3 vlan and just one physical link, for this reason we need that all data passing through a single link, how do we fix that? Creating 3 sub-interfaces, one for each vlan , however it reduces the bandwidth one third. Physical Interfaces: we need it when we have more physical links than vlans We  configure a normal ip in each interface, (one per vlan), now in the switch instead of create trunk links, we create access links (one per vlan). Router(config)#interface FastEthernet0/0 Router(config-subif)# ip address 10.10.10.1 255.255.255.0 Router(config)interface FastEthernet0/1 Router(config-subif)# ip address 10.10.20.1 255.255.255.0 Router(config)#interface FastEthernet0/3 Router(config-subif)#ip address 10.10.30.1 255.255.255.0 Switch(config)#interface range fa0/1, fa0/10 Switch(config-if)#switchport mode access Switch(config-if)#switchport access vlan 10 Switch(config)#interface range fa0/5,fa0/20 Switch(config-if)#switchport mode access Switch(config-if)#switchport access vlan 20 Switch(config)#interface range fa0/8, fa0/30 Switch(config-if)#switchport mode access Switch(config-if)#switchport access vlan 30 Here we have one link per vlan and we  can use the full bandwidth of each interface. I hope you find this answer useful, we will help you with any doubt that you have, if you found this answer useful please mark the question as Answered and rate the anwer. Thanks for using our forum. Greetings, Johnnatan Rodriguez Miranda. ... View more