Cisco BPX 8650, Installation And Configuration Manual

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C H A P T E R
24-1
Cisco BPX 8600 Series Installation and Configuration
Release 9.3.30, Part Number 78-12907-01 Rev. E0, May 2005
24
Configuring BXM Virtual Trunks
This chapter describes the Broadband Switch Module (BXM) virtual trunks.
Contents of this chapter include:
•
Overview
•
How Virtual Trunking Works
•
Connection Management
• General Procedures to Set Up Virtual Trunking
•
Virtual Trunk Across an ATM Network Example
•
Command Overview
Note Virtual trunking is a purchased feature; Cisco Customer Service must enable it on each node where
you intend to use virtual trunking.
Overview
Virtual trunking provides connectivity for Cisco switches through a public ATM cloud as shown in
Figure 24-1. Because a number of virtual trunks can be configured across a physical trunk interface,
virtual trunks provide a cost effective means of connecting across a public ATM network. Each virtual
trunk typically uses only part of a physical trunk’s resources. Yet, like regular trunks, virtual trunks can
carry high-priority traffic.
The hybrid network configuration provided by virtual trunking allows private virtual trunks to use the
mesh capabilities of the public network in interconnecting the subnets of the private network.
A virtual trunk is simply “a trunk defined over a public ATM service.” The trunk really does not exist as a
physical line in the network. You use an additional level of reference, called a
virtual trunk number , to
differentiate the virtual trunks found within a physical port.
You establish connectivity through a public ATM cloud by allocating virtual trunks between the nodes on the
edge of the cloud. With only a single trunk port attached to a single ATM port in the cloud, a node uses the
virtual trunks to connect to multiple destination nodes on the other side of the cloud. From the perspective of
a Cisco node, a virtual trunk is equivalent to a Virtual Path Connection (VPC) provided by the ATM cloud
network, which provides connectivity through the cloud.