1. Network layer devices combine multiple broadcast domains
VLAN to VLAN Overview
Fast E0/0
Router on a stick
802.1q
VLAN 1
VLAN 2
Application
TCP
Purpose: This figure shows a router on a stick being used to interconnect VLANs.
Emphasize: The VLANs are on different networks. Without a network layer device the could not communicate.
Review the protocols operating at each of the OSI layers. IP
ISL
Ethernet
Network layer devices combine multiple broadcast domains

2. Dividing a Physical Interface into Subinterfaces
FastEthernet 0/0
FastEthernet 0/0.1
FastEthernet 0/0.2
FastEthernet 0/0.3
Physical interfaces can be divided into multiple subinterfaces
Purpose: This figure shows a subinterface example. Subinterfaces will be covered further in this course.
Emphasize: At this point, it is important for students t understand that if they want to connect multiple VLANs, they need a separate connection for each VLAN. This can be accomplished by establishing a physical connection for each VLAN that will interconnect with other VLANs or by splitting a trunk into multiple, logical subinterfaces.

3. 802.1q Encapsulation Enables 802.1q on a subinterface
Router(config-subif)#encapsulation dot1q vlan
Enables 802.1q on a subinterface
Purpose: This figure shows the command used to enable ISL on a router interface.
Emphasize: Each interface or subinterface connected to a VLAN must be using the same Data Link protocol. In this case, the protocol is ISL. The figure describes how to encapsulate ISL on an interface or subinterface.

4. Routing Between VLANs Fast E0/0 802.1q VLAN 1 VLAN 2
interface fastethernet 0/0 no ip address ! interface fastethernet 0/0.1 ip address encapsulation dot1q 1 interface fastethernet 0/0.2 ip address encapsulation dotlq 2
Purpose: This figure shows the configuration of the router on a stick.
Emphasize: Highlight the two different networks, and , interconnecting.