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CHAPTER

15-1

Catalyst 3550 Multilayer Switch Software Configuration Guide

78-11194-09

Configuring 802.1Q and Layer 2 Protocol

Tunneling

Virtual private networks (VPNs) provide enterprise-scale connectivity on a shared infrastructure, often

Ethernet-based, with the same security, prioritization, reliability, and manageability requirements of

private networks. Tunneling is a feature designed for service providers (SPs) who carry traffic of

multiple customers across their networks and who are required to maintain the VLAN and Layer 2

protocol configurations of each customer without impacting the traffic of other customers. The

Catalyst 3550 switch supports IEEE 802.1Q tunneling and Layer 2 protocol tunneling.

Note For complete syntax and usage information for the commands used in this chapter, refer to the command

reference for this release.

This chapter contains these sections:

• Understanding 802.1Q Tunneling, page 15-1

• Configuring 802.1Q Tunneling, page 15-4

• Understanding Layer 2 Protocol Tunneling, page 15-7

• Configuring Layer 2 Protocol Tunneling, page 15-9

• Monitoring and Maintaining Tunneling Status, page 15-17

Understanding 802.1Q Tunneling

Business customers of SPs often have specific requirements for VLAN IDs and the number of VLANs

to be supported. The VLAN ranges required by different customers in the same SP network might

overlap, and traffic of customers through the infrastructure might be mixed. Assigning a unique range of

VLAN IDs to each customer would restrict customer configurations and could easily exceed the VLAN

limit (4096) of the 802.1Q specification.

Using the tunneling feature, SPs can use a single VLAN to support customers who have multiple

VLANs. Customer VLAN IDs are preserved, and traffic from different customers is segregated within

the SP network, even when they appear to be in the same VLAN. Tunneling expands VLAN space by

using a VLAN-in-VLAN hierarchy by again tagging the tagged packets. A port configured to support

802.1Q tunneling is called a tunnel port. When you configure tunneling, you assign a tunnel port to a

VLAN ID that is dedicated to tunneling. Each customer requires a separate SP VLAN ID, but that SP

VLAN ID supports all of the customer’s VLANs.

Cisco Catalyst 3550 Series User Manual

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