Pfc3Bxl Or Pfc3B Mode Mpls Qos Overview; Specifying The Qos In The Ip Precedence Field - Cisco 7604 Configuration Manual

Chapter 42 Configuring PFC3BXL or PFC3B Mode MPLS QoS

PFC3BXL or PFC3B Mode MPLS QoS Overview

PFC3BXL or PFC3B mode MPLS QoS enables network administrators to provide differentiated types
of service across an MPLS network. Differentiated service satisfies a range of requirements by supplying
for each transmitted packet the service specified for that packet by its QoS. Service can be specified in
different ways, for example, using the IP precedence bit settings in IP packets.

Specifying the QoS in the IP Precedence Field

When you send IP packets from one site to another, the IP precedence field (the first three bits of the
DSCP field in the header of an IP packet) specifies the QoS. Based on the IP precedence marking, the
packet is given the treatment configured for that quality of service. If the service provider network is an
MPLS network, then the IP precedence bits are copied into the MPLS EXP field at the edge of the
network. However, the service provider might want to set QoS for an MPLS packet to a different value
determined by the service offering.
In that case, the service provider can set the MPLS EXP field. The IP header remains available for the
customer's use; the QoS of an IP packet is not changed as the packet travels through the MPLS network.
For more information, see the
PFC3BXL or PFC3B Mode MPLS QoS
This section describes how PFC3BXL or PFC3B mode MPLS QoS works.
Figure 42-1
Figure 42-1
Host A
The network is bidirectional, but for the purpose of this document the packets move left to right.
In Figure
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•
•
•
OL-4266-08
shows an MPLS network of a service provider that connects two sites of a customer network.
MPLS Network Connecting Two Sites of a Customer's IP Network
IP
network
CE1 PE1
42-1, the symbols have the following meanings:
CE1—Customer equipment 1
PE1—Service provider ingress label edge router (LER)
P1—Label switch router (LSR) within the core of the network of the service provider
P2—LSR within the core of the network of the service provider
Cisco 7600 Series Router Cisco IOS Software Configuration Guide, Release 12.2SX
"MPLS DiffServ Tunneling Modes" section on page
MPLS
network
P1 P2
Owned by
service provider
PFC3BXL or PFC3B Mode MPLS QoS Overview
42-32.
MPLS
network
IP
network
PE2 CE2
Host B
42-5