Chapter 6: Inter-VLAN Routing

The CCNP Exam Topics Covered in This Chapter Include the Following:

• Understand VLAN trunking protocols including 802.1Q, ISL, and the dynamic trunking protocol

• Describe inter-VLAN routing and name the components

• Configure access ports for static membership of single and multiple VLANs

• Configure ports as 802.1Q trunks and verify their operation

• Configure ports as ISL trunks and verify their operation

• Identify the Cisco Route Switch processors and explain how they are implemented

First, let’s have a quick review. Routers break up broadcast domains and layer 2 switches are used to break up collision domains. If you connect all your switches together, they will be in one broadcast domain. You can break up broadcast domains in layer 2 switched networks by creating virtual LANs (VLANs). However, the hosts within a VLAN can communicate only within the same VLAN by default.

Obviously you can not bridge together VLANs because that would allow the forwarding of broadcasts across the VLAN boundary, and would just create a larger single VLAN. For devices in one VLAN to communicate with devices in a different VLAN, they must be routed through a layer 3 device. This is called inter-VLAN routing. You can perform inter-VLAN routing with internal route processors in a layer 2 switch or with an external router called an external route processor.

In this chapter, we cover both internal route processors and external route processors and how to configure them for inter-VLAN configuration.

Note 

The term route processor is used commonly when discussing the device used for inter-VLAN communications, but we should be clear. This is really just a router, either running externally or as firmware or software in a switch. Modern implementations of route processors run IOS and support routing protocols in common with routers.