Chapter 12. VLAN Trunking Protocol

This chapter covers the following key topics:

• Understanding VTP Explains what VTP is and why it is used.

• VTP Modes Compares and demonstrates VTP server, client and transparent modes.

• The Working Mechanics of VTP Describes the various VTP messages such as summary and subset advertisements, advertisement requests, and pruning messages.

• Configuring VTP Mode Provides various configuration examples that illustrate VTP operations and troubleshooting tools.

• VTP Pruning: Advanced Traffic Management Explains how VTP pruning works, and how to configure it.

A number of Catalyst 5000/6000 features are specific to Cisco's LAN switching products. For example, this includes VLAN Trunking Protocol (VTP) described in this chapter as well as features described in other chapters. These features enhance how the Catalyst performs in the network and ease administrative burdens inherent in large LAN implementations. The Catalyst can operate without many, if not all, of the advanced features detailed in this and other chapters. You will, however, find administering and configuring your network cumbersome without them.

For example, the steps for creating a VLAN are to assign a Catalyst to a management domain, create the VLAN, and assign ports to the VLAN. One of the features covered in this chapter, VLAN Trunking Protocol (VTP), helps to minimize configuration efforts by helping with the first two steps. Without VTP, you need to perform these steps in every Catalyst in your network. With VTP, you only need to perform the first two steps at selected devices. This chapter details how VTP operates and how to configure it in your network and provides guidelines on when to exercise some of its features and when not to.

Dynamic VLANs are another feature intended to ease administrative burdens. Dynamic VLANs enable the Catalyst to configure ports to a VLAN automatically based upon the MAC address of the attached device. Chapter 5, "VLANs," covers dynamic VLANs and the VMPS server and client and details how to configure it.

Some advanced features in the Catalyst provide network performance enhancements by reducing the amount of flooded traffic in your network. A bridge deals with certain kinds of traffic, broadcast, multicast, and unknown unicast traffic, by flooding it throughout the bridged network. The Catalyst is a bridge, and, therefore, floods this traffic too. This chapter describes a mechanism for controlling flooded traffic in your network: VTP pruning. VTP pruning eliminates flooding by only flooding VLAN traffic over a trunk port if it needs to. VTP helps the Catalyst make the need to determination. This chapter describes the feature and details how to configure it on the 5000/6000 models.