Configuring Layer 2 Protocol Tunneling

This chapter describes how to configure Layer 2 protocol tunneling in Cisco IOS Release 12.2SX.

Note•For complete syntax and usage information for the commands used in this chapter, see the Cisco IOS Master Command List, at this URL:

http://www.cisco.com/en/US/docs/ios/mcl/allreleasemcl/all_book.html

•The WS-X6548-GE-TX, WS-X6548V-GE-TX, WS-X6148-GE-TX, and WS-X6148V-GE-TX switching modules do not support Layer 2 protocol tunneling.

Tip For additional information about Cisco Catalyst 6500 Series Switches (including configuration examples and troubleshooting information), see the documents listed on this page:

http://www.cisco.com/en/US/products/hw/switches/ps708/tsd_products_support_series_home.html

Participate in the Technical Documentation Ideas forum

This chapter consists of these sections:

•Understanding Layer 2 Protocol Tunneling

•Configuring Support for Layer 2 Protocol Tunneling

Understanding Layer 2 Protocol Tunneling

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 27-1).

•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 27-1) builds a spanning tree topology on switches 1, 2, and 3 without considering convergence parameters based on switches 4 and 5. To provide a single spanning tree domain for the customer, a generic scheme to tunnel BPDUs was created for control protocol PDUs (CDP, STP, and VTP). This process is referred to as Generic Bridge PDU Tunneling (GBPT).

Figure 27-1 Layer 2 Protocol Tunneling Network Configuration

GBPT provides a scalable approach to PDU tunneling by software encapsulating the PDUs in the ingress edge switches and then multicasting them in hardware. All switches inside the service provider network treat these encapsulated frames as data packets and forward them to the other end. The egress edge switch listens for these special encapsulated frames and deencapsulates them; they are then forwarded out of the tunnel.

The encapsulation involves rewriting the destination media access control (MAC) address in the PDU. An ingress edge switch rewrites the destination MAC address of the PDUs received on a Layer 2 tunnel port with the Cisco proprietary multicast address (01-00-0c-cd-cd-d0). The PDU is then flooded to the native VLAN of the Layer 2 tunnel port. If you enable Layer 2 protocol tunneling on a port, PDUs of an enabled protocol are not sent out. If you disable Layer 2 protocol tunneling on a port, the disabled protocols function the same way they were functioning before Layer 2 protocol tunneling was enabled on the port.

Configuring Support for Layer 2 Protocol Tunneling

Note•Encapsulated PDUs received by an 802.1Q tunnel port are transmitted from other tunnel ports in the same VLAN on the switch.

•Configure jumbo frame support on Layer 2 protocol tunneling ports:

–See the "Configuring Jumbo Frame Support" section.

–Take note of the modules listed in the "Configuring Jumbo Frame Support" section that do not support jumbo frames.

To configure Layer 2 protocol tunneling on a port, perform this task:

 
Command
Purpose

Step 1 

Router(config)# interface type1  slot/port

Selects the LAN port to configure.

Step 2 

Router(config-if)# switchport

Configures the LAN port for Layer 2 switching.

•You must enter the switchport command once without any keywords to configure the LAN port as a Layer 2 interface before you can enter additional switchport commands with keywords.

•Required only if you have not entered the switchport command already for the interface.

Step 3 

Router(config-if)# l2protocol-tunnel [cdp | lldp | stp | vtp]

Configures the Layer 2 port as a Layer 2 protocol tunnel port for all protocols or only the specified protocol.

Router(config-if)# l2protocol-tunnel drop-threshold {[cdp | lldp | stp | vtp] packets}

(Optional) Configures the port as a Layer 2 protocol tunnel port and sets a drop threshold for all protocols or only the specified protocol.

Router(config-if)# l2protocol-tunnel shutdown-threshold {[cdp | lldp | stp | vtp] packets}

(Optional) Configures the port as a Layer 2 protocol tunnel port and sets a shutdown threshold for all protocols or only the specified protocol.

Step 4 

Router(config-if)# no lldp transmit

(Required on PE ports) Disables LLDP.

Note CDP is automatically disabled.

Step 5 

Router(config)# end

Exits configuration mode.

Step 6 

Router# show l2protocol-tunnel [interface type1 slot/port|summary]

Verifies the configuration.

1 type = fastethernet, gigabitethernet, or tengigabitethernet

When you configure a Layer 2 port as a Layer 2 protocol tunnel port, note the following information:

•Optionally, you may specify a drop threshold for the port. The drop threshold value, from 1 to 4096, determines the number of packets to be processed for that protocol on that interface in one second. When the drop threshold is exceeded, PDUs for the specified protocol are dropped for the remainder of the one-second period. If a drop threshold is not specified, the value is 0 (drop threshold disabled).

•Optionally, you may specify a shutdown threshold for the port. The shutdown threshold value, from 1 to 4096, determines the number of packets to be processed for that protocol on that interface in one second. When the shutdown threshold is exceeded, the port is put in errdisable state. If a shutdown threshold is not specified, the value is 0 (shutdown threshold disabled).

•If you specify both a drop threshold and a shutdown threshold for the port, packets exceeding the drop threshold will not be forwarded but will be counted toward the shutdown threshold.

Note See the Cisco IOS Master Command List for more information about the l2ptguard keyword for the following commands:

•errdisable detect cause

•errdisable recovery

This example shows how to configure Layer 2 protocol tunneling and drop and shu tdown thresholds on port 5/1 for CDP, STP, and VTP, and verify the configuration: 

Router# configure terminal 

Router(config)# interface fastethernet 5/1 

Router(config-if)# switchport 

Router(config-if)# l2protocol-tunnel shutdown-threshold cdp 400 

Router(config-if)# l2protocol-tunnel shutdown-threshold stp 400 

Router(config-if)# l2protocol-tunnel shutdown-threshold vtp 400 

Router(config-if)# l2protocol-tunnel drop-threshold vtp 200 

Router(config-if)# no lldp transmit 

Router(config-if)# end 

Router# show l2protocol-tunnel summary 

COS for Encapsulated Packets: 5

Drop Threshold for Encapsulated Packets: 0

 
   
 
    
   
 
    
Port      Protocol    Shutdown            Drop                  Status

 
   
 
    
   
 
    
                      Threshold           Threshold             

 
   
 
    
   
 
    
                      (cdp/lldp/stp/vtp)  (cdp/lldp/stp/vtp)

 
   
 
    
   
 
    
-------- ------------ ------------------- -------------------- ----------

 
   
 
    
   
 
    
Fa5/1    -- -- -- ---  400/----/ 400/ 400 ----/----/----/ 200   down(trunk)

 
   
 
    
   
 
    
 
   
 
    
   
 
    
Router# 

 
   
 
    
   
 
    
 
   
 
    
   
 This example shows how to display counter information for port 5/1: 
 
    
   
 
    
Router# show l2protocol-tunnel interface fastethernet 5/1

 
   
 
    
   
 
    
COS for Encapsulated Packets: 5

 
   
 
    
   
 
    
 
   
 
    
   
 
    
Port        Protocol Thresholds          Counters

 
   
 
    
   
 
    
                     Shutdown  Drop      Encap     Decap     Drop

 
   
 
    
   
 
    
----------- -------- --------- --------- --------- --------- ---------

 
   
 
    
   
 
    
Router# 

 
   
 
    
   
 
    
 
   
 
    
   
 This example shows how to clear the Layer 2 protocol tunneling configuration from port 5/1: 
 
    
   
 
    
Router(config-if)# no l2protocol-tunnel shutdown-threshold cdp 400

 
   
 
    
   
 
    
Router(config-if)# no l2protocol-tunnel shutdown-threshold stp 400

 
   
 
    
   
 
    
Router(config-if)# no l2protocol-tunnel shutdown-threshold vtp 400

 
   
 
    
   
 
    
Router(config-if)# no l2protocol-tunnel drop-threshold vtp 200 

 
   
 
    
   
 Router(config-if)# no l2protocol-tunnel cdp 
 
    
   
 Router(config-if)# no l2protocol-tunnel stp 
 
    
   
 
    
Router(config-if)# no l2protocol-tunnel vtp

 
   
 
    
   
 
    
Router(config-if)# lldp transmit 

 
   
 
    
   
 
    
Router(config-if)# end

 
   
 
    
   
 
    
Router# show l2protocol-tunnel summary

 
   
 
    
   
 
    
COS for Encapsulated Packets: 5

 
   
 
    
   
 
    
Drop Threshold for Encapsulated Packets: 0

 
   
 
    
   
 
    
 
   
 
    
   
 
    
Port      Protocol    Shutdown            Drop                  Status

 
   
 
    
   
 
    
                      Threshold           Threshold             

 
   
 
    
   
 
    
                      (cdp/lldp/stp/vtp)  (cdp/lldp/stp/vtp)

 
   
 
    
   
 
    
-------- ------------ ------------------- -------------------- ----------

 
   
 
    
   
 
    
 
   
 
    
   
 
    
Router#

 
   
 
    
   
 
    
 
   
 
    
   
 This example shows how to clear Layer 2 protocol tunneling port counters: 
 
    
   
 
    
Router# clear l2protocol-tunnel counters

 
   
 
    
   
 
    
Router# 

 
   
 
    
   
 
    
 
   
 
   
 
     
   
 
   
 
    
   
 Tip For additional information about Cisco Catalyst 6500 Series Switches (including configuration examples and troubleshooting information), see the documents listed on this page: 
 
    
   
 http://www.cisco.com/en/US/products/hw/switches/ps708/tsd_products_support_series_home.html 
 
    
   
 Participate in the Technical Documentation Ideas forum