Cisco WS-SUP32-GE-3B - Supervisor Engine 32 Software Configuration Manual page 671

Chapter 39 Configuring MPLS QoS
disposition on any router in the packet's path. The color must be reflected everywhere at all levels. For
example, if a packet's QoS marking is changed in the MPLS network, the IP QoS marking reflects that
change.
Figure 39-3
CE1
IP
dscp
3
*In both the MPLS-to-MPLS and the MPLS-to-IP cases, the PHBs of the topmost popped
label is copied into the new top label or the IP DSCP if no label remains
The procedure varies according to whether IP precedence bit markings or DSCP markings are present.
The following actions occur if there are IP precedence bit markings:
IP packets arrive in the MPLS network at PE1, the service provider edge router.
1.
A label is copied onto the packet.
2.
If the MPLS EXP field value is recolored (for example, if the packet becomes out-of-rate because
3.
too many packets are being transmitted), that value is copied to the IGP label. The value of the BGP
label is not changed.
At the penultimate hop, the IGP label is removed. That value is copied into the next lower level label.
4.
When all MPLS labels have been removed from the packet that is sent out as an IP packet, the IP
5.
precedence or DSCP value is set to the last changed EXP value in the core.
The following is an example when there are IP precedence bit markings:
At CE1 (customer equipment 1), the IP packet has an IP precedence value of 3.
1.
When the packet arrives in the MPLS network at PE1 (the service provider edge router), the IP
2.
precedence value of 3 is copied to the imposed label entries of the packet.
The MPLS EXP field in the IGP label header might be changed within the MPLS core (for example,
3.
at P1) by a mark down.
Because the IP precedence bits are 3, the BGP label and the IGP label also contain 3 because in Uniform
Note
mode, the labels always are identical. The packet is treated uniformly in the IP and MPLS networks.
OL-11439-03
Uniform Mode Operation
Assume something recolors the topmost label here to 0
MPLS
PE1 P1
MPLS MPLS
exp 3 exp 0
MPLS MPLS
exp 3 exp 3
IP IP
dscp dscp
3 3
Catalyst Supervisor Engine 32 PISA Cisco IOS Software Configuration Guide, Release 12.2ZY
MPLS DiffServ Tunneling Modes
P2 PE2
*
*
MPLS
exp 0
IP
dscp
3
CE2
IP
dscp
0
39-33