Cisco 7604 Configuration Manual page 736

Understanding PFC3BXL or PFC3B Mode MPLS QoS
After the PFC3BXL or PFC3B applies the port trust and QoS policies, it assigns the internal DSCP. The
PFC3BXL or PFC3B then assigns the EXP value based on the internal DSCP-to-EXP global map for the
labels that it imposes. If more than one label is imposed, the EXP value is the same in each label. The
PFC3BXL or PFC3B preserves the original IP ToS when the MPLS labels are imposed.
The PFC3BXL or PFC3B assigns the egress CoS based on the internal DSCP-to-CoS global map. If the
default internal DSCP-to-EXP and the internal DSCP-to-CoS maps are consistent, then the egress CoS
has the same value as the imposed EXP.
If the ingress port receives both IP-to-IP and IP-to-MPLS traffic, classification should be used to
separate the two types of traffic. For example, if the IP-to-IP and IP-to-MPLS traffic have different
destination address ranges, you can classify traffic on the destination address, and then apply IP ToS
policies to the IP-to-IP traffic and apply a policy (that marks or sets the EXP value in the imposed MPLS
header) to the IP-to-MPLS traffic. See the following two examples:
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Classification for IP-to-MPLS PFC3BXL or PFC3B Mode MPLS QoS
PFC3BXL or PFC3B mode MPLS QoS at the ingress to PE1supports:
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PFC3BXL or PFC3B mode MPLS QoS at the egress of PE1 supports the mpls experimental topmost
command.
Classification at IP-to-MPLS Ingress Port
Classification for IP- to- MPLS is the same as for IP-to-IP. LAN port classification is based on the
received Layer 2 802.1Q CoS value. OSM and FlexWAN interfaces classify based on information in the
received Layer 3 IP header.
Classification at IP-to-MPLS Egress Port
LAN port classification is based on the received EXP value and the egress CoS values is mapped from
that value.
OSM and FlexWAN interfaces classify traffic when you use the match mpls experimental command to
match on the egress CoS as a proxy for the EXP value. The match mpls experimental command does
not match on the EXP value in the topmost label.
If the egress port is a trunk,the LAN ports and the OSM GE-WAN ports copy the egress CoS into the
egress 802.1Q field.
Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
42-10
A PFC3BXL or PFC3B policy to mark IP ToS sets the internal DSCP—If it is applied to all traffic,
then for IP-to-IP traffic, the egress port will rewrite the CoS (derived from the internal DSCP) to the
IP ToS byte in the egress packet. For IP-to-MPLS traffic, the PFC3BXL or PFC3B will map the
internal DSCP to the imposed EXP value.
A PFC3BXL or PFC3B policy to mark MPLS EXP sets the internal DSCP—If it is applied to all
traffic, then for IP-to-IP traffic, the egress port rewrites the IP ToS according to the ingress IP policy
(or trust). The CoS is mapped from the ToS. For IP-to-MPLS traffic, the PFC3BXL or PFC3B will
map the internal DSCP to the imposed EXP value.
Matching on IP precedence or DSCP values or filtering with an access group
The set mpls experimental imposition and police commands
Chapter 42 Configuring PFC3BXL or PFC3B Mode MPLS QoS
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