• The need for end user devices to reach non-local hosts
• The need for hosts on different VLANs to communicate

When a device needs to make a connection to a remote host, it checks its routing table to determine if a known path exists. If the remote host falls into a subnet that it knows how to reach, then the system checks to see if it can connect along that interface. If all known paths fail, the system has one last option, the default route. This route is a special type of gateway route, and it is usually the only one present in the system. On a router, an asterisk (*) indicates a default route in the output of the show ip route command. For hosts on a local area network, this gateway is set to whatever machine has a direct connection to the outside world, and it is the Default Gateway listed in the workstation TCP/IP settings. If the default route is being configured for a router which itself is functioning as the gateway to the public Internet, then the default route will point to the gateway machine at an Internet service provider (ISP) site. Default routes are implemented using the ip route command.

Router(Config)#ip route 0.0.0.0 0.0.0.0 192.168.1.1

In this example, 192.168.1.1 is the gateway. Inter-VLAN connectivity can be achieved through either logical or physical connectivity.

Logical connectivity involves a single connection, or trunk, from the switch to the router. That trunk can support multiple VLANs. This topology is called a router on a stick because there is a single connection to the router. However, there are multiple logical connections between the router and the switch.

Physical connectivity involves a separate physical connection for each VLAN. This means a separate physical interface for each VLAN.

Early VLAN designs relied on external routers connected to VLAN-capable switches. In this approach, traditional routers are connected via one or more links to a switched network. The router-on-a-stick designs employ a single trunk link that connects the router to the rest of the campus network. Inter-VLAN traffic must cross the Layer 2 backbone to reach the router where it can move between VLANs. Traffic then travels back to the desired end station using normal Layer 2 forwarding. This out-to-the-router-and-back flow is characteristic of router-on-a-stick designs.

Interactive Media Activity Drag and Drop: Inter-VLAN Routing Issues and Solutions When the student has completed this activity, the student will learn about some of the problems when using VLAN. They will also learn some of the solutions.