pipe model by attaching IP policies to egress interfaces to reset the traffic class/color
combinations based on the IP header. However, this method requires that the outgoing
packets to be IP. If the outgoing packets are MPLS, then this short pipe model of queuing
is not supported.
Uniform Model
The uniform model of tunneling renders MPLS transparent to the differentiated services
operation. From the diff-serv perspective, it is as if MPLS is not used. In the uniform model,
if traffic conditioning is applied somewhere along the LSP, the EXP bits of the inner header
must be changed at the egress when the inner header becomes the outer header (because
of the pop of the outer label).
To specify whether MPLS uses the pipe or uniform model of tunneling for differentiated
services:
•
Issue the mpls tunnel-model command.
host1(config)#mpls tunnel-model uniform
Related Topics For detailed information about QoS, see the JunosE Quality of Service Configuration
Guide
•
• Configuring MPLS and Differentiated Services on page 303
• Configuring the Tunneling Model for Differentiated Services on page 304
• mpls tunnel-model
EXP Bits for Differentiated Services Overview
MPLS matches on the EXP bits for incoming traffic to set the traffic class/color
combination, and sets the EXP bits for outgoing traffic based on the traffic class/color
combination.
Incoming Traffic
For incoming MPLS traffic, the traffic class/color combination is set according to the EXP
bits in the outermost label, either per the policy attached to the label or per the per-VR
rules. The policy has precedence over the per-VR rules. Therefore, fabric queuing is always
based on the outer label's EXP bits.
If the traffic is label-switched through the router, the EXP bits value associated with the
incoming label that is used for switching—which can be either an outermost label or an
inner label after popping one or more outer labels—is passed onto the egress line module.
This behavior enables the EXP bits value to be copied to outgoing labels, used to reset
the traffic class/color combination on the egress module, or both.
Outgoing Traffic
Outgoing traffic is queued according to traffic class/color combinations. The applied
combination can be the same as was set on the ingress line module, or it can be reset
on the egress line module by egress IP policy.
Copyright © 2010, Juniper Networks, Inc.268
JunosE 11.2.x BGP and MPLS Configuration Guide
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