To prevent the value of the EXP bits for a VPN/VC label from being modified by a per-LSP
policy applied for the outer labels or by per-VR traffic class/color rules:
•
Issue the mpls preserve-vpn-exp command.
host1(config)#mpls preserve-vpn-exp
Related Topics EXP Bits for Differentiated Services Overview on page 268•
• Configuring MPLS and Differentiated Services on page 303
• Example Differentiated Services Application and Configuration on page 305
• mpls copy-upc-to-exp
• mpls preserve-vpn-exp
Example Differentiated Services Application and Configuration
Figure 64 on page 306 shows an example topology where a service provider offers the
following differentiated services to its customers over its MPLS network:
•
QoS Internet service—The CE router is managed by the provider and sets the IP
precedence to predefined values. IP policy on the PE router sets the traffic-class/color
combination according to the incoming well-defined IP precedence value. The policy
also sets the UPC value to the incoming well-defined IP precedence value.
•
Plain Internet service—IP policy on the PE router leaves the traffic-class/color
combination as the default value, best-effort/green. The policy sets the UPC to 0.
•
QoS VPN service—For CE-to-PE traffic, the VPN EXP is copied from the IP precedence
value when the PE router pushes VPN stacked labels.
For PE-to-CE traffic, IP policy on the PE router resets the traffic-class/color combination
according to the received, well-defined IP precedence value, so that egress queuing is
based on the IP precedence value. This action takes place on the egress line module.
•
Plain VPN service—For CE-to-PE traffic, the VPN EXP bits are set to 000 when the PE
router pushes VPN stacked labels.
For PE-to-CE traffic, IP policy on the PE router resets the traffic-class/color combination
to the default value, best-effort/green, so that packets are queued as best-effort. The
IP precedence value is left unchanged.
In this example, the provider also offers an inter-AS VPN service. The provider's own
protocol traffic, for example, BGP signaling traffic such as update messages, is also
labeled, with the EXP bits set to the same value as the IP precedence.
The egress queuing of traffic as it leaves the provider is always based on either the VPN
EXP bits as received on the core side in inter-AS case, or the IP precedence value in all
other cases. It is acceptable that fabric queuing is based on the incoming base label's
EXP.
305Copyright © 2010, Juniper Networks, Inc.
Chapter 4: Configuring MPLS
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