Understanding 802.1Q Tunneling - Cisco Catalyst 3550 series Software Configuration Manual

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.
For complete syntax and usage information for the commands used in this chapter, refer to the command
Note
reference for this release.
This chapter contains these sections:
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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.
78-11194-09
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
C H A P T E R
Catalyst 3550 Multilayer Switch Software Configuration Guide
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