Cisco MPLS QoS Configuration Guide: Setting Up Quality of Service for Network Traffic

Restrictions for MPLS QoS

Configuring MPLS QoS Prerequisites for MPLS QoS, on page 1 Restrictions for MPLS QoS, on page 1 Information About MPLS QoS, on page 2 How to Configure MPLS QoS, on page 3 Configuration Examples for MPLS QoS, on page 9 Additional References, on page 12 Feature History for QoS MPLS EXP, on page 12 Prerequisites for MPLS QoS • The switch must be configured as a Multiprotocol Label Switching (MPLS) provider edge (PE) or provider (P) router, which includes the configuration of a valid label protocol and underlying IP routing protocols. Restrictions for MPLS QoS • MPLS classification and marking can only occur in an operational MPLS network.

• If a packet is classified by IP type of service (ToS) or class of service (CoS) at ingress, it cannot be reclassified by MPLS EXP at egress (imposition case). However, if a packet is classified by MPLS at ingress, it can be reclassified by IP ToS, CoS, or Quality of Service (QoS) group at egress (disposition case). • To apply QoS on traffic across protocol boundaries, use QoS-group. You can classify and assign ingress traffic to the QoS-group. Thereafter, you can use the QoS-group at egress to classify and apply QoS. • If a packet is encapsulated in MPLS, the MPLS payload cannot be checked for other protocols, such as IP, for classification or marking.

Only MPLS EXP marking affects packets that are encapsulated by MPLS. • The short pipe mode is not supported to transport packets through the MPLS network. You can transport packets using any one of the following modes—uniform mode or pipe mode. • MPLS classification and marking is not supported on SVI. User needs to apply the policy on either Physical or Port-channel interfaces. Configuring MPLS QoS 1

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MPLS Experimental Field

Information About MPLS QoS This section provides detailed information about MPLS QoS. MPLS QoS Overview The MPLS QoS functionality enables network administrators to provide differentiated services across an MPLS network. Network administrators can satisfy a wide range of networking requirements by specifying the CoS applicable to each transmitted IP packet. Different classes of service can be established for IP packets by setting the IP precedence bit in the header of each packet. Classification, remarking, and queuing on an MPLS network is performed over MPLS EXP bits.

In the MPLS network, the packets are differentiated by the MPLS EXP field marking, and are treated accordingly, depending on the weighted early random detection (WRED) configuration. The MPLS EXP field in MPLS packet allows you to: • Classify traffic The classification process selects the traffic to be marked. Classification accomplishes this by partitioning traffic into multiple priority levels, or classes of service. Traffic classification is the primary component of class-based QoS provisioning. For more information, see “Classifying Network Traffic”. • Police and mark traffic Policing causes traffic that exceeds the configured rate to be discarded or marked to a different drop level.

Marking traffic is a way to identify packet flows to differentiate them. Packet marking allows you to partition your network into multiple priority levels or classes of service. For more information, see “Marking Network Traffic”. • Queueing Queueing helps prevent traffic congestion. This includes priority level queueing, weighted tail drop (WTD), scheduling, shaping and weighted random early detection (WRED) features. MPLS Experimental Field The MPLS experimental bits (EXP) field is a 3-bit field in the MPLS header that you can use to define the QoS treatment (per-hop behavior) that a node should give to a packet.

In an IP network, the DiffServ Code Point (DSCP) (a 6-bit field) defines a class and drop precedence. The EXP bits can be used to carry some of the information encoded in the IP DSCP and can also be used to encode the dropping precedence. By default, Cisco IOS Software copies the three most significant bits of the DSCP or the IP precedence of the IP packet to the EXP field in the MPLS header. This action happens when the MPLS header is initially imposed on the IP packet. However, you can also set the EXP field by defining a mapping between the DSCP or IP precedence and the EXP bits. This mapping is configured using the set mpls experimental or police commands.

For more information, see the “How to Classify and Mark MPLS EXP” section. Configuring MPLS QoS Information About MPLS QoS Configuring MPLS QoS 2

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How to Configure MPLS QoS

Note A policy map configured with set ip dscp is not supported on the provider edge device because the policy action for MPLS label imposition node should be based on set mpls experimental imposition value. However, a policy map with action set ip dscp is supported when both the ingress and egress interfaces are Layer 3 ports. You can perform MPLS EXP marking operations using table-maps. It is recommended to assign QoS-group to a different class of traffic in ingress policy and translate QoS-group to DSCP and EXP markings in egress policy using table-map.

If a service provider does not want to modify the value of the IP precedence field in packets transported through the network, they can use the MPLS EXP field value to classify and mark IP packets. By choosing different values for the MPLS EXP field, you can mark critical packets so that those packets have priority if network congestion occurs. WRED monitors network traffic to anticipate and prevent congestion at common network and internetwork bottlenecks. WRED can selectively discard lower priority traffic when an interface becomes congested. This feature can also provide differentiated performance characteristics for different classes of service.

There are two ways to transport packets through the MPLS network: Uniform mode: Uniform mode of transferring packets operates on one layer of QoS. The Provider Edge at ingress copies the DSCP information from the incoming IP packet into the MPLS EXP bits of the imposed labels and the IP precedence bits are mapped to the MPLS EXP field . As the EXP bits travel through the core, they may or may not be modified by the intermediate devices on the network. The Provider Edge at egress copies the EXP bits to the DSCP bits of the newly exposed IP packet. Pipe mode: Pipe mode of transferring packets operates on two layers of QoS.

An underlying QoS for the data that remains unchanged when traversing the core. A per-core QoS, which is separate from that of the underlying IP packets. The DSCP information is saved and stored as the packet travels through the MPLS network. The MPLS EXP label is applied by the PE at ingress but the IP precedence bits are not stored. At egress, the original IP precedence value is preserved. Benefits of MPLS EXP Classification and Marking The QoS EXP Matching feature allows you to classify, mark and queue network traffic by modifying the Multiprotocol Label Switching (MPLS) experimental bits (EXP) field.

If a service provider does not want to modify the value of the IP precedence field in packets transported through the network, they can use the MPLS EXP field value to classify and mark IP packets. By choosing different values for the MPLS EXP field, you can mark critical packets so that those packets have priority if network congestion occurs. How to Configure MPLS QoS This section provides information about how to configure MPLS QoS: Configuring MPLS QoS Benefits of MPLS EXP Classification and Marking Configuring MPLS QoS 3

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Marking MPLS EXP on the Outermost Label

Classifying MPLS Encapsulated Packets You can use the match mpls experimental topmost command to define traffic classes based on the packet EXP values, inside the MPLS domain. You can use these classes to define services policies to mark the EXP traffic using the police command. Procedure Marking MPLS EXP on the Outermost Label Perform this task to set the value of the MPLS EXP field on imposed label entries. Before you begin Marking MPLS packets at imposition is used with ingress classification on IP ToS or CoS fields. Configuring MPLS QoS Classifying MPLS Encapsulated Packets Command or Action Purpose Step 1 enable Example: Device> enable Enables privileged EXEC mode.

Enter your password if prompted. Step 2 configure terminal Example: Device# configure terminal Enters global configuration mode. Step 3 class-map [match-all | match-any] class-map-name Example: Device(config)# class-map exp3 Creates a class map to be used for matching traffic to a specified class, and enters class-map configuration mode. Enter the class map name. Step 4 match mpls experimental topmost mpls-exp-value Example: Device(config-cmap)# match mpls experimental topmost 3 Specifies the match criteria. Note The match mpls experimental topmost command classifies traffic on the basis of the EXP value in the topmost label header. Step 5 end Example:

Device(config-cmap)# end (Optional) Returns to privileged EXEC mode. Configuring MPLS QoS 4

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