Figure 64 shows an example topology where a service provider offers the following differentiated services to its customers over its MPLS network:
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.
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.
Figure 64: Differentiated Services over an MPLS Network