How Qos Works For Mpls Traffic; Mpls Qos And Packet Priority During Congestion; Interfaces Supporting Mpls Qos - Cisco 10000 Series Configuration Manual

MPLS QoS

How QoS Works for MPLS Traffic

The Cisco 10000 series router bypasses the IP header-based classification for MPLS packets—you
cannot classify MPLS packets into distinct classes using the embedded IP header of the MPLS packet.
The router classifies MPLS packets as belonging to the class-default class, except if you specify
qos-group or input-interface match statements for traffic classes.
Normal QoS processing applies to incoming IP packets that the router later tags. Normal QoS processing
resumes for outgoing IP packets that arrived tagged.
Precedence-based Weighted Random Early Detection (WRED) uses the MPLS experimental (EXP)
value for MPLS packets.
Upon MPLS imposition, by default the router sets the EXP values of all pushed labels to the packet's IP
precedence value. Upon label swap, the new label carries the EXP value of the swapped label. A set or
police command directive might modify the default EXP setting.

MPLS QoS and Packet Priority During Congestion

The router classifies packets based on the classification and marking criteria you define, such as a source
address, destination address, port, protocol identification, or class of service field. The packets'
classification in turn determines each packet's priority and how the router treats the packet during
periods of congestion (for example, forward or drop the packet).
For example, service level agreements (SLAs), contracted between providers and their customers,
specify how much traffic the service provider agrees to deliver. Packets that comply with the
agreed-upon rate are considered in-rate and packets that do not comply are considered out-of-rate.
During congestion, the router gives preferential treatment to in-rate packets and might aggressively drop
out-of-rate packets.

Interfaces Supporting MPLS QoS

The following describes interface support for MPLS QoS:
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Cisco 10000 Series Router Quality of Service Configuration Guide
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The router supports the match mpls experimental topmost command on both input and output
interfaces on which MPLS is enabled.
The set mpls experimental imposition command and the set mpls experimental command are
supported on the provider edge (PE) router input interface connecting to customer edge (CE) router.
You can also use these commands on input interfaces on the CE, in pipe mode of MPLS QoS
DiffServ tunneling models.
The set mpls experimental imposition command replaces the set mpls experimental
Note
command, which the router supports only for backward compatibility. We recommend that
you use the set mpls experimental imposition command.
The set-mpls-exp-imposition-transmit action of the police command is only supported on the PE
input interface that is connected to the CE.
The mpls ip encapsulate explicit-null command is supported on the CE router interface that is
connected to the PE. This command is only used in pipe mode of MPLS QoS DiffServ tunneling
models.
Chapter 20 Configuring Quality of Service for MPLS Traffic
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