Cisco BPX 8650, Installation And Configuration Manual

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24-6
Cisco BPX 8600 Series Installation and Configuration
Release 9.3.30, Part Number 78-12907-01 Rev. E0, May 2005
Chapter 24 Configuring BXM Virtual Trunks
How Virtual Trunking Works
Figure 24-4 Virtual Trunks across a Public ATM Network
Routing with Virtual Trunks
Automatic Routing Management, PNNI, and MPLS each use different routing mechanisms. However,
the routing mechanisms meet the following criteria when dealing with virtual trunks:
•
Virtual Trunk Existence—Specifies that routing has special restrictions and conid assignments for
a virtual trunk. For example, VPCs may not be routed over a virtual trunk.
• Traffic Classes—Specifies the unique characteristics of CBR, VBR, and ABR traffic are maintained
through the cloud as long as the correct type of virtual trunk is used. You configure the traffic classes
allowed per virtual trunk by using the
cnftrk command. The routing algorithm excludes virtual
trunks whose traffic class is not compatible with the candidate connection to be routed.
•
Connection Identifier (Connid) Capacity—Specifies that each virtual trunk has a configurable
number of connection channels reserved from the card. The routing algorithm checks for adequate
channel availability on a virtual trunk before selecting the trunk for a route.
The characteristics of a virtual trunk used by connection routing are maintained throughout the network.
Virtual trunk existence, traffic classes, and connection channels are sent to every node to allow the
routing algorithm to use the trunk correctly. Routing uses only those virtual trunks that can support the
traffic type of the connection.
Public ATM network
ATM-UNI
ATM-UNI
17712
BXM 4
IGX 10
4.3.1
10.2.1
4.3
10.2
VPCs within the cloud,
one for each virtual trunk
(virtual trunks can be
type CBR, VBR, or ABR)
BPX_A
IGX_A
BXM 5
BPX_B
4.3.2
10.2.3
5.1.1
5.1.2
5.1