Cisco Systems 6500, EA6500 Understanding How Layer 2 Protocol Tunneling Works

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Catalyst 6500 Series Switch Cisco IOS Software Configuration Guide—Release 12.1 E

78-14099-04

Chapter 14 Configuring IEEE 802.1Q Tunneling and Layer 2 Protocol Tunneling

Understanding How Layer 2 Protocol Tunneling Works

This example shows how to configure tunneling on port 4/1 and verify the configuration:

Router# configure terminal

Router(config)# interface fastethernet 4/1

Router(config-if)# switchport mode dot1qtunnel

Router(config-if)# end

Router# show dot1q-tunnel interface

The vlan dot1q tag native command is a global command that configures the switch to tag native VLAN

traffic, and admit only 802.1Q tagged frames on 802.1Q trunks, dropping any untagged traffic, including

untagged traffic in the native VLAN.

To configure the switch to tag traffic in the native VLAN, perform this task:

This example shows how to configure the switch to tag native VLAN traffic and verify the configuration:

Router# configure terminal

Router(config)# vlan dot1q tag native

Router(config)# end

Router# show vlan dot1q tag native

Understanding How Layer 2 Protocol Tunneling Works

Layer 2 protocol tunneling allows Layer 2 protocol data units (PDUs) (CDP, STP, and VTP) to be

tunneled through a network. This section uses the following terminology:

• Edge switch—The switch connected to the customer switch and placed on the boundary of the

service provider network (see Figure 14-3).

• Layer 2 protocol tunnel port—A port on the edge switch on which a specific tunneled protocol can

be encapsulated or deencapsulated. The Layer 2 protocol tunnel port is configured through CLI

commands.

• Tunneled PDU—A CDP, STP, or VTP PDU.

Without Layer 2 protocol tunneling, tunnel ports drop STP and VTP packets and process CDP packets. This

handling of the PDUs creates different spanning tree domains (different spanning tree roots) for the

customer switches. For example, STP for a VLAN on switch 1 (see Figure 14-3) builds a spanning tree

Step 4 Router(config-if)# end Exits configuration mode.

Step 5 Router# show dot1q-tunnel [{interface type

interface-number}]

Verifies the configuration.

1. type = ethernet, fastethernet, gigabitethernet, or tengigabitethernet

Command Purpose

Step 1 Router(config)# vlan dot1q tag native Configures the switch to tag native VLAN traffic.

Router(config)# no vlan dot1q tag native Clears the configuration.

Step 2 Router(config)# end Exits configuration mode.

Step 3 Router# show vlan dot1q tag native Verifies the configuration.