l2pt技术的基本原理及实现
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2010-01-04
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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 7600 Series Router Cisco IOS Command Reference 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
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
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).
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