Cisco ASR 903 Router Chassis Software Configuration Guide, IOS XE Release 3.9

Global QoS Limitations

The following limitations apply to multiple QoS features for the Cisco ASR 903 Series Router:

• When EVCs under a physical interface have a QoS policy attached, the following limitations apply:

– The port-level policy is limited to the class-default class

– Only the shape command is supported in the port-level policy

• The Cisco ASR 903 Series Router supports up to 64 unique QoS classification service instances in a given bridge domain. QoS service instances refer to ports, VLAN classes, EFPs associated with a QoS classification policy.
• Modification of class-map definitions while applied to an interface or Ethernet Flow Point is not supported.
• Policy validation—Some QoS policy configurations are not validated until you apply the policy-map to an interface or Ethernet Flow Point. If a QoS configuration is invalid, the router rejects the configuration when you apply it to an interface. In some cases, a QoS configuration may be rejected due to hardware resource exhaustion or limitations. If you receive such an error message, detach the policy and adjust your QoS configuration.
• The match-all keyword is supported only for QinQ classification.
• SAToP and CESoPSN pseudowire traffic has a default MPLS Exp priority setting of 5 (high).
• QoS is supported on POS interfaces on optical interface module.
• Three-level QoS policies are not supported on the OC-3/OC-12 serial, MLPPP, and PoS interfaces. You can only apply QoS policies on two levels on these interfaces.
• QoS does not account for CRC values on an interface and assumes that the value is 2 bytes. CRC differences can cause accuracy issues for 2 to 3% of the 128-byte traffic.
• The Cisco ASR 903 router supports a maximum of 128 internal and reserved labels that represent PHB (cos/dscp/exp/prec) values on a QoS policy. A label exhaustion message is displayed if a policy exceeds the maximum number of labels.

QoS Features Using MQC Limitations

Table 13-3 lists the QoS MQC scaling limitations on router per release.

Etherchannel QoS Limitations

An EtherChannel bundles individual Ethernet links into a single logical link that provides the aggregate bandwidth of up to eight physical links. Release 3.9 introduces support for QoS policies on layer 3 Etherchannel interfaces.

The following features are supported on either etherchannels or member links, ingress and egress direction:

• Marking
• Policing

Note You cannot configure these features on an etherchannel interface and a member link at the same time.

The following features are supported only on member links:

• shaping
• bandwidth
• priority
• QL/WRED

Ingress QoS

Restrictions for Ingress QoS in the Cisco IOS Release 3.9 and later:

• EC main interface

– Only policing and marking are supported.

– A class-map can have any type of filter, including the match vlan and match service instance commands.

• EC EVC/TEFP

– Only policing and marking are supported.

– Match service instance is not supported.

• Member links

– Only policing and marking are supported.

– Policy-map on a member link is not supported with EVC configured at the port-channel level.

• Policy-map application is allowed only on the EC main interface, EC member link, or EC EVC.
• Ingress TCAM entries are used even if no member links exist for a policy on the EC main interface and EC EVCs.

Egress QoS

Restrictions for Egress QoS in the Cisco IOS XE Release 3.9 and later:

• EC main interface

– Classification statistics for the policy-map on a port-channel main interface are not supported as no queues are allocated for a port-channel main interface.

– Policing and marking actions are only allowed in the policy-map on a port-channel main interface.

– Queuing actions are not supported.

– Egress TCAM entries are used even in the absence of member links.

• EC EVC/TEFP

– Classification statistics for the policy-map on port-channel EVC/TEFP are not supported as no queues are allocated for port-channel EVC/TEFP.

– Policing and marking actions are only allowed in the policy-map on port-channel EVC/TEFP.

– Queuing actions are not supported.

– Egress TCAM entries are used even if there are no member links present.

• EC Member links

– For egress match service-instance policy-map on EC member links, the same policy must be present on all other EC member links.

– Match service-instance policy-map is replicated automatically for all the member links when the first policy is applied on any of the member links.

– For non-match service-instance policy-map, the same policy-map can be applied for all member-links.

– Dynamic modification of match service-instance policy-map actions is not allowed.

– Deleting a global match service instance policy-map is not allowed if it applied to the member links.

– Policing, marking and queuing action are supported on port-channel member links.

– The running configuration displays the first member link on the first policy applied in a service-policy configuration.

– The s how policy-map interface brief command only displays the policy-map applied on the running configuration.

– Applying a same policy again on other member links where a policy-map was already applied will not display any error. A differently named policy if applied again will display an error.

– For match service instance policy-map on egress member links, the policy-map statistics information is reset, when a member link is added or deleted from a port-channel either by configuration or by LACP port-bundling/unbundling action.

– There is no difference in behavior for non-match service instance policies on the member links. They continue to work in the legacy mode. There is no conservation of TCAM entries in this mode, even if the same policy is applied on all member links.

– Policy-map application is allowed only on either EC main interface, or EC member link, or EC EVC.

Routed Port-Channel

Routed Port-channel Interface

The following features are supported for the ingress policy-map on a routed port-channel interface:

• Marking
• Policing
• Conditional marking
• Marking and policing
• Classification criteria is prec, dscp or ip acl.

This is an example:

The following features are supported for egress policy-map on routed port-channel interface:

• Marking
• Policing
• Classification criteria is prec or dscp.

This is an example:

Member-links on Routed Port-channel Interface

The following features are supported for ingress policy-map on member links on the routed port-channel interface:

• Marking
• Policing
• Conditional marking
• marking and policing
• Classification criteria is prec, dscp or ip acl.

The following features are supported for egress policy-map on member links on the routed port-channel interface:

• Shaping
• Queue-limit
• Bandwidth (kbps, percent)
• Bandwidth remaining (ratio, percent)
• WRED
• Port Shaper
• Low Latency Queue (LLQ or priority queue)

This is an example:

Port-channel with EFP

The following features are supported for ingress policy-map on port-channel on EFP:

• Marking
• Policing
• Conditional marking
• marking and policing
• The classification criteria is VLAN or EFP, Cos in child.

This is an example:

The following features are supported for egress policy-map on port-channel on EFP:

• Marking
• Policing
• Conditional marking
• marking and policing
• The classification criteria is VLAN or EFP, Cos in child

This is an example:

EFP of Port-channel with EFP Configuration

• The following features are supported for ingress and egress policy-map on EFP of port-channel on EFP:

– Marking

– Policing

– Conditional marking

– marking and policing

– The classification criteria is VLAN or EFP, Cos in child.

Note Match EFP is cannot be configured.

Member Links of Port-channel with EFP Configuration

• The following features are supported for ingress and egress policy-map on member links of port-channel on EFP:

– Marking

– Policing

– Conditional marking

– marking and policing

– The classification criteria is VLAN or EFP, Match VLAN and Cos in child.

Restrictions for Hierarchical Policies

The Cisco ASR 903 Router supports hierarchical QoS policies with up to three levels, allowing for a high degree of granularity in traffic management.

There are limitations on the supported classification criteria at each level in the policy-map hierarchy. The following limitations apply when configuring hierarchical policy-map classification:

• The topmost policy-map in a three-level hierarchy only supports classification using class-default.

Sample Hierarchical Policy Designs

The following are examples of supported policy-map configurations:

• Three-Level Policy—You can only apply a three-level policy to a physical port on the router. A three-level policy consists of:

– Topmost policy: class-default

– Middle policy: match vlan

– Lowest policy: match qos-group/match prec/match cos/match dscp

The following sample policy uses a flat class-default policy on the port and VLAN policies on EFP interfaces to unique QoS behavior to each EFP.

Sample Policy

• Two-Level Policy

– Topmost policy: match vlan

– Lowest policy: match qos-group/match prec/match cos/match dscp

• Two-Level Policy

– Topmost policy: class-default

– Lowest policy: match vlan

• Two-Level Policy

– Topmost policy: class-default

– Lowest policy: match mpls experimental topmost

• Flat policy: match ip dscp
• Flat policy: match vlan inner
• Flat policy: class-default

Ingress and Egress Hierarchical Policing

In releases before Cisco IOS XE Release 3.9, policing was supported only at one level in the ingress and egress policy. It was only at the PHB or class level.

Effective with Cisco IOS XE Release 3.9, policing is supported at two levels of the policy-map.

• Ingress policing

– Port and EFP level

– EFP and Class level

– Port and Class level

• Egress policing

– EFP and Class level

– Port and Class level

Note Egress hierarchical policing is supported on two levels but one of the levels must be Class level.

If an Ingress hierarchal policy is configured on the interface, the show Ethernet service instance interface command does not display the service instance statistics.

The class-level in an Egress hierarchal policy is configured internally as shaper.

MPLS VPN QoS Mapping

Table 13-4 summarizes the default MPLS mappings for the Cisco ASR 903 Series Router.

Note You can modify the default mapping behaviors using explicit marking policies.

QoS Policer and Shaper Calculation

Table 13-5 summarizes the packet accounting information used to make policer and shaper calculations on the Cisco ASR 903 Series Router.

The following considerations also apply when understanding QoS policer and shaper calculations:

• Egress shaping is applied at layer 1.
• Ingress packet length accounting is performed at egress.
• Egress shaping and policing do not account for newly pushed VLAN tags and MPLS labels.
• If two policers are configured at egress, the statistics on the child PHB or PQ level are not displayed.

Implementing MPLS Diffserv Tunneling Modes

The MPLS specification defines three Diffserv operation modes:

• Uniform—There is only one DiffServ marking that is relevant for a packet when traversing the MPLS network.
• Pipe—The network uses two markings for traffic: the original marking value, which is used once the packets leave the MPLS network, and a separate marking value that is used while the traffic crosses intermediate nodes on the LSP span. The second marking value is dropped when traffic exits the MPLS network.
• Short-Pipe—the egress LSR uses the original packet marking instead of using the marking used by the intermediate LSRs.

The following sections describe how to implement these modes on the Cisco ASR 903 Series Router using QoS policies.

Implementing Uniform Mode

Use the following guidelines to implement uniform mode on the Cisco ASR 903 Series Router:

Imposition

To copy the diffserv value to the MPLS Exp bit, create a QoS configuration as follows:

• Option 1

– Classify based on Prec bit or DSCP bit at ingress.

– Set the qos-group.

– Classify on qos-group.

– Set the MPLS exp value.

• Option 2

– Classify based on Prec bit or DSCP bit at ingress.

– Set the mpls Exp bit at imposition.

Tag-to-tag Transfer

To ensure that outer tag values are copied to inner tags, explicitly mark the outer Exp value on the inner Exp bit.

Disposition

To copy the MPLS Exp bit to the diffserv/IP prec bit, create a QoS configuration as follows:

• Classify based on MPLS Exp bit on the ingress interface.
• Set the qos-group value.
• Classify based on qos-group on the egress interface.
• Mark the IP prec or DSCP bit.

Implementing Pipe Mode

Use the following guidelines to implement pipe mode on the Cisco ASR 903 Series Router:

Imposition

To set the MPLS Exp bit by policy, create a QoS configuration as follows:

• Option 1

– Set the qos-group on the egress interface.

– Classify based on qos-group on the egress interface.

– Set the MPLS Exp value.

• Option 2

– Apply the set mpls exp imposition command at ingress.

Disposition

To preserve the original IP Prec or diffserv value so that egress queuing is based on MPLS exp value, create a QoS configuration as follows:

• Classify on MPLS Exp value on the ingress interface.
• Set the qos-group on the egress interface.
• Classify based on qos-group value on the egress interface.

Implementing Short-Pipe Mode

Use the following guidelines to implement short-pipe mode on the Cisco ASR 903 Series Router:

Disposition

To preserve the original IP Prec or diffserv value so that egress queuing is based on MPLS Prec or diffserv value, create a QoS configuration as follows:

• Classify based on IP prec or DSCP value on the egress interface.
• Mark the IP prec or DSCP bit.

Classification

Classifying network traffic allows you to organize packets into traffic classes or categories on the basis of whether the traffic matches specific criteria. Classifying network traffic (used in conjunction with marking network traffic) is the foundation for enabling many quality of service (QoS) features on your network.

• Ingress Classification Limitations
• Egress Classification Limitations
• Additional Classification Limitations
• Classifying Traffic using an Access Control List
• Configuring Multiple match Statements
• Classifying Traffic Using Match EFP Service Instance Feature

Table 13-5 summarizes the QoS Classification limitations for the Cisco ASR 903 Series Router.

Ingress Classification Limitations

The following limitations apply to QoS classification on the Cisco ASR 903 Series Router:

• If you configure egress classification for a class of traffic affected by an input policy-map, you must use the same QoS criteria on the ingress and egress policy-maps.

Egress Classification Limitations

• When applying a QoS policy to a link aggregation group (LAG) bundle, you must assign the policy to a physical link within the bundle; you cannot apply the policy to the LAG bundle or the port channel interface associated with the bundle.
• MPLS Pipe Mode Limitations—When you configure pipe mode for Time to Live (TTL), the router enables pipe mode for QoS as well. When pipe mode is enabled, you cannot enable egress classification based on the header on an egress interface. For example, you cannot classify based on egress DSCP value for MPLS IP packets when the router is in pipe mode.
• If you configure egress classification for a class of traffic affected by an input policy-map, you must use the same QoS criteria on the ingress and egress policy-maps.

Classifying Traffic on MLPPP Interfaces

Release 3.7(1) introduces support for egress QoS on MLPPP interfaces. The Cisco ASR 903 Series Router supports the following match commands in a QoS class-map applied to an egress MLPPP interface.

• match discard-class
• match dscp
• match ip dscp
• match ip precedence
• match precedence
• match qos-group

Additional Classification Limitations

The following additional marking usage guidelines apply in Release 3.9:

• The topmost policy-map in a three-level hierarchy only supports classification using class-default.
• If you configure egress classification for a class of traffic affected by an input policy-map, you must use the same QoS criteria on the ingress and egress policy-maps.

Classifying Traffic using an Access Control List

You can classify inbound packet based on an IP standard or IP extended access control list (ACL). Follow these steps to classify traffic based on an ACL:

1. Create an access list using the access-list or ip access-list commands

2. Reference the ACL within a QoS class map using the match access-group configuration command

3. Attach the class map to a policy map

Limitations and Usage Guidelines

The following limitations and usage guidelines apply when classifying traffic using an ACL:

• QoS ACLs are supported only for IPv4 traffic
• QoS ACLs are supported only for ingress traffic
• You can use QoS ACLs to classify traffic based on the following criteria:

– Source and destination host

– Source and destination subnet

– TCP source and destination

– UDP source and destination

• Named and numbered ACLs are supported.
• You can apply QoS ACLs only to the third level class (bottom-most).
• The following range of numbered access lists are supported:

– 1-99—IP standard access list

– 100-199—IP extended access list

– 1300-1999—IP standard access list (expanded range)

– 2000-2699—IP extended access list (expanded range)

• You must create an ACL before referencing it within a QoS policy.
• Deny statements within an ACL are ignored for the purposes of classification.
• Classifying traffic based on TCP flags using an ACL is not supported.
• Classifying traffic using multiple mutually exclusive ACLs within a match-all class-map is not supported.
• Classifying traffic on a logical/physical level using an ACL is not supported.
• Applying QoS ACLs to MAC addresses is not supported.
• Port matching with the neq keyword is only supported for a single port.
• Matching on multiple port numbers using the eq keyword is supported for up to 8 ports.
• You can only configure 8 port matching operations on a given interface. A given command can consume multiple matching operations if you specify a source and destination port, as shown in the following examples:

– permit tcp any lt 1000 any —Uses one port matching operation

– permit tcp any lt 1000 any gt 2000 —Uses two port matching operations

– permit tcp any range 1000 2000 any 400 500 —Uses two port matching operations

You can use the following commands to verify your configuration:

– show platform hardware pp { active | standby } acl label labelindex— Displays information about security ACL labels; the number of available input VMRs reflects the number of available port range operations.

• Only the following combination of matches are currently supported for Ingress policies:

– Combination A: DSCP, Outer COS, UDP/TCP Source and Destination port number, IP SA/DA

– Combination B: IP SA/DA, Outer COS, Inner COS, DSCP, MPLS EXP

– Combination C: MAC DA, Outer COS, Inner COS, DSCP, MPLS Exp

Note Policy with match on L4 ACL and MPLS EXP together is currently not supported.

For more information about configuring QoS, see http://www.cisco.com/en/US/products/ps11610/products_installation_and_configuration_guides_list.html. For more information about configuring access control lists, see the Security Configuration Guide: Access Control Lists, Cisco IOS XE Release 3S (Cisco ASR 903).

Configuring Multiple match Statements

In IOS XE Release 3.5, the Cisco ASR 903 Series Router supported a single match or match-any command in a given QoS class-map, as shown in the following example:

IOS XE 3.5 Class Map Example

match cos 3

IOS XE Release 3.6 introduces support for multiple match or match-any commands in a given QoS class-map, as shown in the following example:

IOS XE 3.6 Class Map Example

The router treats the statements as a logical OR operation and classifies traffic that matches any match statement in the class map.

Classifying Traffic Using Match EFP Service Instance Feature

Service Provider configurations have various service instances on the PE. QoS policy-maps are applied on these service instances or group of service instances. Cisco IOS XE Release 3.9S introduces the Match EFP Service Instance feature. The benefits of this feature are:

• Identify the various types of service-instances like EFP, Trunk EFPs
• Apply policies on these service instances at the port
• Manage bandwidth and priority across the service instances on the port and across classes within the service instance
• Apply policies on a group of transport service instances such as applying similar policies to a group of EFPs.

Configuring Match Service Instances

Restrictions

• Ethernet service instances configured under the interface can be classified in a class of a policy-map. The class can match on a group or set of match service instance statements.

• Ingress and Egress Match service instance are supported.
• match service instance and match PHB per flows classification are defined at respective levels in the policy hierarchy under the port.
• The number of EFPs supported per group is 256. Only 256 match statements are supported per class.
• Match EFP policy-map can be configured only on the port and not under the service instance.

Example

Marking

QoS marking allows you to set a desired value on network traffic to make it easy for core devices to classify the packet.

• Marking Overview
• Ingress Marking Limitations
• Egress Marking Limitations
• Marking IPv6 Traffic
• Additional Marking Limitations

Table 13-7 summarizes the QoS Marking limitations for the Cisco ASR 903 Series Router.

Marking Overview

The Cisco ASR 903 Series Router supports the following parameters with the set command:

• set cos
• set discard-class
• set ip dscp
• set ip precedence
• set mpls experimental imposition (ingress marking)
• set mpls experimental topmost
• set qos-group

CoS Marking Limitations

The following limitations apply when configuring CoS marking:

• set cos —This set action has no effect unless there is a egress push action to add an additional header at egress. The COS value set by this action will be used in the newly added header as a result of the push rewrite. If there are no push rewrite on the packet, the new COS value will have no effect.
• The set cos inner command is not supported.

Ingress Marking Limitations

The following limitations apply to QoS marking on the Cisco ASR 903 Series Router:

• The Cisco ASR 903 Series Router does not support hierarchical marking.
• You can configure marking and policing for any number of classes on any one of the three levels of the policy-map hierarchy. If you configure marking on one level, you can configure policing without marking (transmit, drop) on another level. Marking and policing are not supported on the same level of a policy-map.?

Egress Marking Limitations

IOS XE Release 3.6 introduces support for egress marking. The following limitations apply when configuring marking on egress interfaces:

• The set cos inner command is not supported.
• The set mpls experimental imposition command is not supported.
• The set mpls experimental topmost command is supported for marking MPLS Exp bits; other commands for marking MPLS Exp bits are not supported.

Marking Traffic on MLPPP Interfaces

Release 3.7(1) introduces support for egress QoS on MLPPP interfaces. The Cisco ASR 903 Series Router supports the following parameters with the set command on egress MLPPP interfaces:

• set ip dscp
• set ip precedence

Marking IPv6 Traffic

The Cisco ASR 903 supports the following commands for marking both IPv4 and IPv6 packets:

• set dscp
• set precedence

For more information about IPv6 QoS, see:

• http://www.cisco.com/en/US/docs/ios/ios_xe/ipv6/configuration/guide/ip6-qos_xe.html
• http://www.cisco.com/en/US/docs/ios/ipv6/configuration/guide/ip6-qos.html

Additional Marking Limitations

The following additional marking usage guidelines apply in Release 3.9:

• CoS marking Limitation— The set cos action has no effect unless there is a egress push action to add an additional header at egress. The COS value set by this action will be used in the newly added header as a result of the push rewrite. If there are no push rewrite on the packet, the new COS value will have no effect.
• The Cisco ASR 903 Series Router does not support hierarchical marking.
• You can configure marking and policing for any number of classes on any one of the three levels of the policy-map hierarchy. If you configure marking on one level, you can configure policing without marking (transmit, drop) on another level. Marking and policing are not supported on the same level of a policy-map.
• Ingress marking is not supported on Etherchannel interfaces or member links.
• Release 3.9 introduces support for ingress MPLS Exp marking on pseudowire CEM and ATM interfaces, including SAToP, CESoPSN, ATM IMA, and ATMoMPLS. For more information about configuring bit marking, see Implementing MPLS Diffserv Tunneling Modes.
• Marking is supported on Etherchannel interfaces and individual member links; however, you cannot configure marking on both interface levels at once.

Policing

Traffic policing allows you to control the maximum rate of traffic sent or received on an interface, and to partition a network into multiple priority levels or class of service (CoS). This section describes the policing limitations and configuration guidelines for the Cisco ASR 903 Series Router.

• Ingress Policing Limitations
• Egress Policing Limitations

The Cisco ASR 903 Series Router supports the following policing types:

• Single-rate policer with two color marker (1R2C) (color-blind mode)
• Two-rate policer with three color marker (2R3C) (color-blind mode)

Table 13-8 summarizes the QoS policing limitations for the Cisco ASR 903 Series Router.

Table 13-8 Policing QoS Limitations

Supported Commands

The Cisco ASR 903 Series Router supports the following policing commands on ingress interfaces:

• police (percent)— police cir percent percentage [ burst-in-msec ] [ bc conform-burst-in-msec ms ] [ be peak-burst-in-msec ms ] [ pir percent percentage ] [ conform-action action [ exceed-action action [ violate-action action ]]]
• police (policy map)— police cir bps [[ bc ] normal-burst-bytes [ maximum-burst-bytes | [ be ] [ burst-bytes ]]] [ pir bps [ be burst-bytes ]] [ conform-action action [ exceed-action action [ violate-action action ]]]
• police (two rates)— police cir cir [ bc conform-burst ] [ pir pir ] [ be peak-burst ] [ conform-action action [ exceed-action action [ violate-action action ]]]

The Cisco ASR 903 Series Router supports the following policing commands on egress interfaces:

• bandwidth (policy-map class)—bandwidth { bandwidth-kbps | remaining percent percentage | percent percentage } [ account { qinq | dot1q } aal5 subscriber-encapsulation ]
• bandwidth remaining ratio — bandwidth remaining ratio ratio [ account { qinq | dot1q } [ aal5 ] { subscriber-encapsulation | user-define d offset }]
• police (policy map)— police cir bps [[ bc ] normal-burst-bytes [ maximum-burst-bytes | [ be ] [ burst-bytes ]]] [ pir bps [ be burst-bytes ]] [ conform-action action [ exceed-action action [ violate-action action ]]]
• priority—priority { bandwidth-kbps | percent percentage } [ burst ]

Several restrictions apply when using egress policing; see the Egress Policing Limitations section for more information.

Supported Actions

The Cisco ASR 903 Series Router supports the following policing actions on ingress interfaces:

– transmit

– drop

– set-qos-transmit

– set-cos-transmit

– set-dscp-transmit