CHAPTER
18-1
Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
OL-4266-08
18
Configuring Layer 2 Protocol Tunneling
This chapter describes how to configure Layer 2 protocol tunneling on the Cisco 7600 series routers.
Note • For complete syntax and usage information for the commands used in this chapter, refer to the Cisco
IOS Master Command List, Release 12.2SX at this URL:
http://www.cisco.com/en/US/docs/ios/mcl/122sxmcl/12_2sx_mcl_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.
This chapter consists of these sections:
• Understanding How Layer 2 Protocol Tunneling Works, page 18-1
• Configuring Support for Layer 2 Protocol Tunneling, page 18-2
Tip For additional information (including configuration examples and troubleshooting information), see the
documents listed on this page:
http://www.cisco.com/en/US/products/hw/routers/ps368/tsd_products_support_series_home.html
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 router—The router connected to the customer router and placed on the boundary of the service
provider network (see Figure 18-1).
• Layer 2 protocol tunnel port—A port on the edge router 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 router 1 (see Figure 18-1) builds a spanning tree
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