Configuring Modular QoS Service Packet Classification

This chapter covers these topics:

Packet Classification Overview

Packet classification involves categorizing a packet within a specific group (or class) and assigning it a traffic descriptor to make it accessible for QoS handling on the network. The traffic descriptor contains information about the forwarding treatment (quality of service) that the packet should receive. Using packet classification, you can partition network traffic into multiple priority levels or classes of service. The source agrees to adhere to the contracted terms and the network promises a quality of service. Traffic policers and traffic shapers use the traffic descriptor of a packet to ensure adherence to the contract.

Traffic policers and traffic shapers rely on packet classification features, such as IP precedence, to select packets (or traffic flows) traversing a router or interface for different types of QoS service. After you classify packets, you can use other QoS features to assign the appropriate traffic handling policies including congestion management, bandwidth allocation, and delay bounds for each traffic class.

The Modular Quality of Service (QoS) CLI (MQC) defines the traffic flows that must be classified, where each traffic flow is called a class of service, or class. Later, a traffic policy is created and applied to a class. All traffic not identified by defined classes fall into the category of a default class.

Traffic Class Elements

The purpose of a traffic class is to classify traffic on your router. Use the class-map command to define a traffic class.

A traffic class contains three major elements:

  • A name

  • A series of match commands - to specify various criteria for classifying packets.

  • An instruction on how to evaluate these match commands (if more than one match command exists in the traffic class)

Packets are checked to determine whether they match the criteria that are specified in the match commands. If a packet matches the specified criteria, that packet is considered a member of the class and is forwarded according to the QoS specifications set in the traffic policy. Packets that fail to meet any of the matching criteria are classified as members of the default traffic class.

This table shows the details of match types that are supported on the router.

Match Type Supported

Min, Max

Max Entries

Support for Match NOT

Support for Ranges

Direction Supported on Interfaces

IPv4 DSCP

IPv6 DSCP

DSCP

(0,63)

64

Yes

Yes

Ingress

IPv4 Precedence

IPv6 Precedence

Precedence

(0,7)

8

Yes

No

Ingress

MPLS Experimental Topmost

(0,7)

8

Yes

No

Ingress

Access-group

Not applicable

8

No

Not applicable

Ingress

QoS-group

(1,7)

(1,511) for peering profile

7

No

No

  • Egress

  • Ingress for QoS Policy Propagation Using Border Gateway Protocol (QPPB)

  • Ingress for peering profile

Traffic-class

(1,7)

7

No

No

  • Egress

CoS

(0,7)

8

No

Yes

Ingress

DEI

(0,1)

1

No

No

Ingress

Protocol

(0,255)

1

Yes

Not applicable

Ingress


Note

Egress queue statistics are displayed only for those classes which have a corresponding match criteria in the egress. Therefore, if you have a set traffic-class x configured in the ingress, you must have a corresponding match traffic-class x in the egress, in order to see the statistics in the egress side.


Note

A maximum value of up to 64 unique queues is supported.

Default Traffic Class

Unclassified traffic (traffic that does not meet the match criteria specified in the traffic classes) is treated as belonging to the default traffic class.

If the user does not configure a default class, packets are still treated as members of the default class. However, by default, the default class has no enabled features. Therefore, packets belonging to a default class with no configured features have no QoS functionality. These packets are then placed into a first in, first out (FIFO) queue and forwarded at a rate determined by the available underlying link bandwidth. This FIFO queue is managed by a congestion avoidance technique called tail drop.

For egress classification, match on traffic-class (1-7) is supported. Match traffic-class 0 cannot be configured. The class-default in the egress policy maps to traffic-class 0 .

This example shows how to configure a traffic policy for the default class: 


configure
 policy-map ingress_policy1
 class class-default
  police rate percent 30
 !

Create a Traffic Class

To create a traffic class containing match criteria, use the class-map command to specify the traffic class name, and then use the match commands in class-map configuration mode, as needed.

Guidelines

  • Users can provide multiple values for a match type in a single line of configuration; that is, if the first value does not meet the match criteria, then the next value indicated in the match statement is considered for classification.

  • Use the not keyword with the match command to perform a match based on the values of a field that are not specified.

  • All match commands specified in this configuration task are considered optional, but you must configure at least one match criterion for a class.

  • If you specify match-any , one of the match criteria must be met for traffic entering the traffic class to be classified as part of the traffic class. This is the default. If you specify match-all , the traffic must match all the match criteria.

  • From Release 7.7.1 onwards, for the match access-group command, QoS classification based on the packet length field in the IPv4 and IPv6 headers is supported. Prior to this, support was not available for packet length and TTL (time to live) fields.

  • For the match access-group command, when an ACL list is used within a class-map, the deny action of the ACL is ignored and the traffic is classified based on the specified ACL match parameters.

    An empty ACL (contains no rules, only remarks), when used within a class-map permits all traffic by default, and the implicit deny condition doesn’t work with an empty ACL. The corresponding class-map matches all traffic not yet matched by the preceding traffic classes.

  • The traffic-class and discard-class are supported only in egress direction, and these are the only match criteria supported in egress direction.

  • The egress default class implicitly matches qos-group 0 for marking policy and traffic-class 0 for queuing policy.

  • Multicast takes a system path that is different than unicast on router, and they meet later on the egress in a multicast-to-unicast ratio of 20:80 on a per interface basis. This ratio is maintained on the same priority level as that of the traffic.

  • Egress QoS for multicast traffic treats traffic classes 0-5 as low-priority and traffic classes 6-7 as high priority. Currently, this is not user-configurable.

  • Egress shaping does not take effect for multicast traffic in the high priority (HP) traffic classes. It only applies to unicast traffic.

  • If you set a traffic class at the ingress policy and do not have a matching class at egress for the corresponding traffic class value, then the traffic at ingress with this class will not be accounted for in the default class at the egress policy map.

  • Only traffic class 0 falls in the default class. A non-zero traffic class assigned on ingress but with no assigned egress queue, falls neither in the default class nor any other class.

Configuration Example

You have to accomplish the following to complete the traffic class configuration:

  1. Creating a class map

  2. Specifying the match criteria for classifying the packet as a member of that particular class

    (For a list of supported match types, see Traffic Class Elements.) 


Router# configure
Router(config)# class-map match-any qos-1
Router(config-cmap)# match qos-group 1
Router(config-cmap)# end-class-map
Router(config-cmap)# commit

Use this command to verify the class-map configuration: 


Router#show class-map qos-1
1) ClassMap: qos-1    Type: qos
    Referenced by 2 Policymaps

Also see, Running Configuration.

Also see, Verification.

Related Topics

Associated Commands

Traffic Policy Elements

A traffic policy contains three elements:

  • Name

  • Traffic class

  • QoS policies

After choosing the traffic class that is used to classify traffic to the traffic policy, the user can enter the QoS features to be applied to the classified traffic.

The MQC does not necessarily require that the users associate only one traffic class to one traffic policy.

The order in which classes are configured in a policy map is important. The match rules of the classes are programmed into the TCAM in the order in which the classes are specified in a policy map. Therefore, if a packet can possibly match multiple classes, only the first matching class is returned and the corresponding policy is applied.

The router supports 32 classes per policy-map in the ingress direction and 8 classes per policy-map in the egress direction.

This table shows the supported class-actions on the router.

Supported Action Types

Direction supported on Interfaces

minimum-bandwidth

egress

bandwidth-remaining

egress

mark

(See Packet Marking)

police

ingress

priority

egress (level 1 to level 7)

queue-limit

egress

shape

egress

wred

egress

WRED supports default and discard-class options; the only values to be passed to the discard-class being 0 and 1.

Create a Traffic Policy

The purpose of a traffic policy is to configure the QoS features that should be associated with the traffic that has been classified in a user-specified traffic class or classes.

To configure a traffic class, see Create a Traffic Class.

After you define a traffic policy with the policy-map command, you can attach it to one or more interfaces to specify the traffic policy for those interfaces by using the service-policy command in interface configuration mode. With dual policy support, you can have two traffic policies, one marking and one queuing attached at the output. See, Attach a Traffic Policy to an Interface.

Configuration Example

You have to accomplish the following to complete the traffic policy configuration:

  1. Creating a policy map that can be attached to one or more interfaces to specify a service policy

  2. Associating the traffic class with the traffic policy

  3. Specifying the class-action(s) (see Traffic Policy Elements) 


Router# configure
Router(config)# policy-map  test-shape-1
Router(config-pmap)# class qos-1

/* Configure class-action ('shape' in this example). 
Repeat as required, to specify other class-actions */
Router(config-pmap-c)# shape average percent 40
Router(config-pmap-c)# exit

/* Repeat class configuration as required, to specify other classes */

Router(config-pmap)# end-policy-map
Router(config)# commit

See, Running Configuration.

See, Verification.

Related Topics

Associated Commands

Attach a Traffic Policy to an Interface

After the traffic class and the traffic policy are created, you must attach the traffic policy to interface, and specify the direction in which the policy should be applied.


Note

When a policy-map is applied to an interface, the transmission rate counter of each class is not accurate. This is because the transmission rate counter is calculated based on the exponential decay filter.

Configuration Example

You have to accomplish the following to attach a traffic policy to an interface:

  1. Creating a traffic class and the associated rules that match packets to the class (see )

  2. Creating a traffic policy that can be attached to one or more interfaces to specify a service policy (see Create a Traffic Policy )

  3. Associating the traffic class with the traffic policy

  4. Attaching the traffic policy to an interface, in the ingress or egress direction 


Router# configure
Router(config)# interface HundredGigE 0/6/0/18
Router(config-int)# service-policy output test-shape-1
Router(config-int)# commit

Running Configuration 


/* Class-map configuration */

class-map match-any traffic-class-1
 match traffic-class 1
 end-class-map
!
- - -
- - -

/* Traffic policy configuration */
policy-map test-shape-1
 class traffic-class-1
  shape average percent 40
 !
 class class-default
 !
 end-policy-map
!
- - -
- - -

/* Attaching traffic policy to an interface in egress direction */ 
interface HundredGigE0/6/0/18
 service-policy output test-shape-1
 !

Verification


Router# show qos interface hundredGigE 0/6/0/18 output 

NOTE:- Configured values are displayed within parentheses Interface HundredGigE0/6/0/18 ifh 0x30001f8  -- output policy
NPU Id:                        3
Total number of classes:       2
Interface Bandwidth:           100000000 kbps
VOQ Base:                      11112
VOQ Stats Handle:              0x88430698
Accounting Type:               Layer1 (Include Layer 1 encapsulation and above)
------------------------------------------------------------------------------
Level1 Class                             =   qos-1
Egressq Queue ID                         =   11113 (LP queue)
Queue Max. BW.                           =   40329846 kbps (40 %)
Queue Min. BW.                           =   0 kbps (default)
Inverse Weight / Weight                  =   1 / (BWR not configured)
Guaranteed service rate                  =   40000000 kbps
TailDrop Threshold                       =   50069504 bytes / 10 ms (default)
WRED not configured for this class

Level1 Class                             =   class-default
Egressq Queue ID                         =   11112 (Default LP queue)
Queue Max. BW.                           =   101803495 kbps (default)
Queue Min. BW.                           =   0 kbps (default)
Inverse Weight / Weight                  =   1 / (BWR not configured)
Guaranteed service rate                  =   50000000 kbps
TailDrop Threshold                       =   62652416 bytes / 10 ms (default)
WRED not configured for this class

Related Topics

Associated Commands

Packet Marking


Note

L2 packet marking is not supported on NC55-24DD and NC55-18DD-SE line cards for Cisco IOS XR Release 7.0.2.

The packet marking feature provides users with a means to differentiate packets based on the designated markings. The router supports egress packet marking. match on discard-class on egress, if configured, can be used for a marking policy only.

The router also supports L2 ingress marking.

For ingress marking:

Ingress traffic— For the ingress pop operation, re-marking the customer VLAN tag (CoS, DEI) is not supported.

Egress traffic— The ingress ‘pop VLAN’ is translated to a ‘push VLAN’ for the egress traffic, and (CoS, DEI) marking is supported for newly pushed VLAN tags. If two VLAN tags are pushed to the packet header at the egress side, both inner and outer VLAN tags are marked. For example:

1. rewrite ingress tag pop 1 symmetric

2. rewrite ingress tag pop 2 symmetric

3. rewrite ingress tag translate 2-to-1 dot1q/dot1ad <> symmetric

Limitations

  • The statistics and counters for the egress marking policy cannot be viewed on the router.

  • QoS EXP matching for egress doesn’t work for Layer 2 VPN and Layer 3 VPN traffic flowing from:

    • Cisco NCS 5700 series line cards at ingress to Cisco NCS 5500 series line cards at the egress

    and

    • from Cisco NCS 5500 series line cards at ingress to Cisco NCS 5700 series line cards at egress.

  • For QOS EXP-Egress marking applied on a Layer 3 interface on Cisco NCS550x and NCS55Ax routers, there is a limit of two unique policy maps per NPU. This limit is three unique policy maps per NPU for routers that have the Cisco NC57 line cards installed.

    You can apply these policies to as many interfaces as your system resources allow. However, if you apply more than the permitted limit of unique policies, you may encounter unexpected failure.

  • For QOS egress marking (CoS, DEI) applied on a Layer 2 interface, there is a limit of 13 unique policy-maps per NPU. If you exceed this number, you may encounter unexpected failure.

Supported Packet Marking Operations

This table shows the supported packet marking operations.

Supported Mark Types

Range

Support for Unconditional Marking

Support for Conditional Marking

set cos

0-7

ingress

No

set dei

0-1

ingress

No

set discard-class

0-3

ingress

No

set dscp

0-63

ingress

No

set mpls experimental topmost

0-7

ingress

No

set precedence

0-7

ingress

No

set QoS-group

0-7

ingress

No

set traffic-class

0-7

ingress

No

Class-based Unconditional Packet Marking

The packet marking feature allows you to partition your network into multiple priority levels or classes of service, as follows:

  • Use QoS unconditional packet marking to set the IP precedence or IP DSCP values for packets entering the network. Routers within your network can then use the newly marked IP precedence values to determine how the traffic should be treated.

    On ingress direction, after matching the traffic based on either the IP Precedence or DSCP value, you can set it to a particular discard-class. Weighted random early detection (WRED), a congestion avoidance technique, thereby uses discard-class values to determine the probability that a packet is dropped.

  • Use QoS unconditional packet marking to assign MPLS packets to a QoS group. The router uses the QoS group to determine how to prioritize packets for transmission. To set the traffic class identifier on MPLS packets, use the set traffic-class command in policy map class configuration mode.


    Note
    Setting the traffic class identifier does not automatically prioritize the packets for transmission. You must first configure an egress policy that uses the traffic class.

  • Use QoS unconditional packet marking to assign packets to set the priority value of IEEE 802.1p/
Inter-Switch Link (ISL) packets. The router uses the CoS value to determine how to prioritize packets for transmission and can use this marking to perform Layer 2-to-Layer 3 mapping. To set the Layer 2 CoS value of an outgoing packet, use the set cos command in policy map configuration mode.

  • Use QoS unconditional packet marking to mark a packet based on the drop eligible indicator value (DEI) bit on 802.1ad frames. To set the DEI value, use the set dei command to set the drop eligible indicator value (DEI) in policy map class configuration mode.


Note

  • Unless otherwise indicated, the class-based unconditional packet marking for Layer 3 physical interfaces applies to bundle interfaces.

QoS Re-marking of IP Packets in Egress Direction

The router support the marking of IP DSCP bits of all IP packets to zero, in the egress direction. This feature helps to re-mark the priority of IP packets, which is mostly used in scenarios like IP over Ethernet over MPLS over GRE. This functionality is achieved using the ingress policy-map with set dscp 0 option configured in class-default.

Configuration Example


Router# configure
Router(config)# policy-map ingress-set-dscp-zero-policy
Router(config-pmap)# class class-default 
Router(config-pmap-c)# set dscp 0
Router(config-pmap-c)# end-policy-map
Router(config-pmap)# commit

Running Configuration


policy-map ingress-set-dscp-zero-policy
class class-default
  set dscp 0
! 
end-policy-map
!

QoS Re-marking of Ethernet Packets in Egress Direction

The router supports Layer 2 marking of Ethernet packets in the egress direction.

QoS L2 Re-marking of Ethernet Packets in Egress Direction

The router supports Layer 2 marking of Ethernet packets in the egress direction.

To enable this feature, you must:

  • Configure the policy maps for queuing and marking at the egress interface.

  • Set traffic-class in the ingress and use match traffic-class in the egress for queuing.

  • Ensure that the set qos-group command is configured in ingress policy and the corresponding match qos-group command is configured in the egress marking policy. If there is no corresponding QoS group, you will experience traffic failure.

    The ingress ‘push VLAN’ is translated to ‘pop VLAN’ for the egress traffic. In this case, (CoS, DEI) re-marking is not supported for the VLAN tag. For example:

    1. rewrite ingress tag push dot1q/dot1ad <> symmetric

    2. rewrite ingress tag push dot1q/dot1ad <> second-dot1q <> symmetric

    3. rewrite ingress tag translate 1-to-2 dot1q/dot1ad <> second-dot1q <> symmetric

Running Configuration
policy-map egress-marking
class qos1
set cos 1
! 
class qos2
set cos 2
set dei 1
! 
class qos3
set cos 3
! 
class class-default
set cos 7
! 
end-policy-map
!

QoS L2 Re-Marking of Ethernet Packets on L3 Flows in Egress Direction

The router supports Layer 2 marking of Ethernet packets on Layer 3 flows in the egress direction.

To enable this feature, you must:

  • Configure the policy maps for marking at the egress interface.

  • Ensure that the set qos-group command is configured in ingress policy and the corresponding match qos-group command is configured in the egress marking policy. If there is no corresponding QoS group, you will experience traffic failure.

Restrictions

The following restrictions apply while configuring the Layer 2 marking of Ethernet packets on Layer 3 flows in the egress direction.

  • set discard-class is not supported in ingress policy with peering mode.

  • Egress marking statistics are not available.

  • Layer 2 (802.1p) Egress marking is supported on Layer 3 flows for these types of traffic: IP-to-IP, IP-to-MPLS, and MPLS-to-IP traffic.

  • Layer 2 marking of Ethernet packets on Layer 3 flows in the egress direction is supported only in the peering mode.

Running Configuration

Ingress Policy:

You must first set up the qos-group at ingress. 

class-map match-any Class0
 match mpls experimental topmost 0
 match precedence routine
 match dscp 0-7
 end-class-map
class-map match-any Class1
 match mpls experimental topmost 1
 match precedence priority
 match dscp 8-15
 end-class-map
class-map match-any Class2
 match mpls experimental topmost 2
 match precedence immediate
 match dscp 16-23
 end-class-map
class-map match-any Class3
 match mpls experimental topmost 3
 match precedence flash
 match dscp 24-31
 end-class-map
class-map match-any Class4
 match mpls experimental topmost 4
 match precedence flash-override
 match dscp 32-39
 end-class-map
class-map match-any Class5
 match mpls experimental topmost 5
 match precedence critical
 match dscp 40-47
 end-class-map
class-map match-any Class6
 match mpls experimental topmost 6
 match precedence internet
 match dscp 48-55
 end-class-map
class-map match-any Class7
 match mpls experimental topmost 7
 match precedence network
 match dscp 56-63
 end-class-map
!

policy-map ncs_input
 class Class7
  set traffic-class 7
  set mpls experimental imposition 7
  set qos-group 7
!
 class Class6
  set traffic-class 6
  set mpls experimental imposition 6
  set qos-group 6
!
 class Class5
  set traffic-class 5
  set mpls experimental imposition 5
  set qos-group 5
!
 class Class4
  set traffic-class 4
  set mpls experimental imposition 4
  set qos-group 4
 !
 class Class3
  set traffic-class 4
  set mpls experimental imposition 3
  set qos-group 3
 !
 class Class2
  set traffic-class 2
  set mpls experimental imposition 2
  set qos-group 2
 !
 class Class1
  set traffic-class 2
  set mpls experimental imposition 1
  set qos-group 1
 !
 class Class0
  set traffic-class 0
  set mpls experimental imposition 0
  set qos-group 0
 !
 end-policy-map
!

Egress Policy:

At the egress, run these commands to mark the packets.

class-map match-any qos7
match gos-group 7
 end-class-map
!
class-map match-any qos6
match gos-group 6
 end-class-map
!
class-map match-any qos5
match qos-group 5
 end-class-map
!
class-map match-any qos4
match gos-group 4
 end-class-map
!
class-map match-any qos3
match gos-group 3
 end-class-map
!
class-map match-any qos2
 match gos-group 2
 end-class-map
!
class-map match-any qos1
match gos-group 1
 end-class-map
!

policy-map ncs_output
 class qos7
  set cos 7
  set dei 1
!
 class qos6
  set cos 6
  set dei 1
!
 class qos5
  set cos 5
  set dei 1
!
 class qos4
  set cos 4
  set dei 1
!
 class qos3
  set cos 3
  set dei 1
!
 class qos2
  set cos 2
  set dei 1

!
 class qos1
  set cos 1
  set dei 1
!
 end-policy-map
!

Bundle Traffic Policies

A policy can be bound to bundles. When a policy is bound to a bundle, the same policy is programmed on every bundle member (port). For example, if there is a policer or shaper rate, the same rate is configured on every port. Traffic is scheduled to bundle members based on the load balancing algorithm.

Both ingress and egress traffic is supported. Percentage-based policies , absolute rate-based policies, and time-based policies are supported.


Note

Egress marking is not supported on BVI interfaces.

For details, see Configure QoS on Link Bundles.

Ingress Short-Pipe

When QoS traffic leaves an MPLS network, the MPLS label stack is removed on the penultimate ingress Label Switch Router (LSR), leaving an IPv4 or IPv6 packet to be forwarded. MPLS experimental bits (or EXP or pipe mode) carries out this disposition process and the packet is marked with a Differentiated Services Code Point (DSCP) or precedence value (also called DSCP or Precedence-based classification).

Usually, QoS traffic supports DSCP and precedence-based classifications only when there is no MPLS label in the packet. Using the ingress short-pipe feature, however, you can classify a packet that contains one MPLS label using the type-of-service (ToS) field of the IPv4 or IPv6 header. This classification method is called ingress short-pipe. To classify an IP packet this way, you must:

  1. Create a child class map.

  2. Specify a ToS value in the child class map.

  3. Attach the child class map to a parent class map.

  4. Create a policy map containing the parent class map.

  5. Set any ingress action such as traffic class or QoS group.

With the ingress short-pipe feature, you get an increased visibility into traffic packets. Plus, the feature also removes the limitation of classifying MPLS packets that come into IPv4 or IPv6 networks.

Restrictions and Other Important Points

Ensure that you read these points before you configure the ingress short-pipe feature.

  • This feature isn’t supported on:

    • NC57-24DD

    • NC57-18DD-SE

    • NC57-36H-SE

    • NC57-36H6D-S

    • NC57-MOD-S

    • NCS-57B1-6D24-SYS

    • NCS-57B1-5DSE-SYS

    • NCS-57C3-MOD-SYS

    • NCS-57D2-18DD-SYS

  • This feature works only when there is one MPLS header in the traffic packet. If there are two or more MPLS headers, the ingress-short pipe feature fails. For example, in case of Explicit Null where there are two labels at the disposition, this feature will not work.

  • You can carry out ingress classification using either the MPLS experimental bits (or EXP or pipe mode) classification OR the DSCP/precedence (or short-pipe) classification. Ensure that you do not mix the classification methods, else it may result in an unknown behavior, and the classification may not work at all.

  • This feature is supported only on L3VPN, and not supported on L2VPN.

  • This feature works for regular IPv4/IPv6 traffic, but will not work for IPv6 VPN Provider Edge over MPLS (6VPE).

  • You can add only one child class map to a parent class map.

  • This feature supports the invocation of short-pipe and legacy DSCP classification for the same parent class map.

  • The child class map can contain only match precedence and match dscp commands.

  • This feature is not supported in peering mode.

Configure Ingress Short-Pipe

This section details a sample configuration for the ingress short-pipe feature and another sample to configure classification for labeled and non-labeled packets under the same parent class.

Sample configuration to classify a packet that contains one MPLS label using the type-of-service (ToS) field of the IPv4 or IPv6 header (or the ingress short-pipe method):

class-map match-any in_pipe
 match mpls disposition class-map child_pipe 
end-class-map
!
class-map match-any child_pipe
 match precedence 1 
match dscp ipv4 af11
 end-class-map
!
class-map match-any ingress-business-high
match dscp af21 af22
end-class-map

class-map match-any ingress-business-low
match dscp af11 af12
end-class-map

policy-map ingress-classifier
class in_pipe
set traffic-class 5

class ingress-business-high
set traffic-class 4
class ingress-business-low
set traffic-class 2
class class-default
set traffic-class 0
!

You can configure classification for both labeled and non-labeled packets under the same parent class as in the following sample configuration. In this example, for MPLS labeled packets, DSCP configured under the child class is classified, while for non-labeled packets, DSCP/ToS configured in the match dscp <value> statement is classified.

DSCP value range is from 0 through 63. The range option is not supported. Up to 8 items per class are supported. Up to 64 match dscp values in total. 

class-map match-any in_pipe
match mpls disposition class-map child_pipe  (labeled case)
match dscp af11 (non-labeled case)
end-class-map
!
class-map match-any child_pipe
match precedence 1 
match dscp ipv4 af11
end-class-map
!
class-map match-any ingress-business-high
match dscp af21 af22
end-class-map
 
class-map match-any ingress-business-low
match dscp af11 af12
end-class-map
 
policy-map ingress-classifier
class in_pipe
set traffic-class 5

class ingress-business-high
set traffic-class 4
class ingress-business-low
set traffic-class 2
class class-default
set traffic-class 0
!

Associated Commands

  • match mpls disposition class-map

Selective Egress Policy-Based Queue Mapping

With selective egress policy-based queue mapping, you can combine traffic class (TC) maps in various permutations at the egress.


Note

Modular chassis do not support this feature.

The primary aim of introducing the egress TC (traffic class) mapping is to classify the traffic in the ingress using a single policy and place the classified traffic into queues, by assigning the traffic classes. At the egress, you can support different grouping of TCs.

Based on different Service Level Agreements (SLAs) that each customer has signed up for, you can group some TCs into priority queues for real time (RT) traffic, other TCs into guaranteed bandwidth (BW) traffic, and the rest into best effort (BE) traffic delivery.

Let us consider an example where three customers have purchased these services, based on their requirements:

  • Customer A - Requires RT traffic, reserved BW traffic and BE traffic delivery.

  • Customer B – Requires reserved BW traffic and BE traffic delivery.

  • Customer C – Needs only BE traffic delivery.

Using the selective egress policy-based queue mapping, you can create three profiles this way:

  • Customer A – Priority queue RT traffic (TC1), Guaranteed BW traffic (TC3), Best effort traffic (TC0, TC5)

  • Customer B – Guaranteed BW traffic (TC1), Best effort traffic (TC0, TC3, TC5)

  • Customer C - Best effort traffic (TC0, TC1, TC3, TC5)

Using the egress TC-mapping, you can create three different profiles that you can use for each customer based on their SLAs with the provider.

Figure 1. Selective Egress Policy-Based Queue Mapping Helps Create Customer Profiles Based on Their SLAs

Restrictions and Other Important Points

Ensure that you read these points before you configure the selective egress policy-based queue-mapping feature.

  • There can be only one TC (Traffic Class) mapped class to a PM (Policy Map).

  • You cannot use a TC that you used in a mapped class, in a non-mapped class under the same PM.

  • You can have a maximum of three unique TC mapped PMs or profiles per platform.

  • Every TC mapped class must include traffic-class 0 in the range values.

  • The TC-mapping range is from 0 through 5.

  • When a TC-mapped class is present in a PM, the class default becomes a dummy class. This means that the class default statistics and QoS values are not applicable.

  • All the class default limitations apply to the TC-mapped class; for example, you cannot configure priority command under the TC mapped class.


Note

A TC-mapped PM or profile is a PM that contains a TC-mapped class.

Example of a TC-mapped class:

match traffic-class 0 1 2 3

Example of a TC non-mapped class:

match traffic-class 1

Configure Selective Egress Policy-Based Queue Mapping

This section details a sample configuration for the selective egress policy-based queue-mapping feature and a use case to show how this feature works.

Sample configuration


class-map match-any <name>
 match traffic-class <value>
commit

policy-map tc_pmap
 class tc035
  shape average percent 1 
 ! 
 class class-default
! 
 end-policy-map
! 
 class-map match-any tc035
match traffic-class 0 3 5 
 end-class-map
!

Verification

Run the show qos interface and show policy-map interface commands.

When TC mapping class is present in a policy map, the class default does not have any values calculated.

show qos interface bundle-Ether 44 output sample 

NOTE:- Configured values are displayed within parentheses
NPU Id:                        0
Total number of classes:       3
Interface Bandwidth:           100000000 kbps
Policy Name:                   tc_pmap
Accounting Type:               Layer1 (Include Layer 1 encapsulation and above)
------------------------------------------------------------------------------
Level1 Class                             =   tc1
 
Level1 Class                             =   tc035
 
Level1 Class                             =   class-default
 
Interface HundredGigE0/0/0/30 Ifh 0xf000208 (Member) -- output policy
NPU Id:                        0
Total number of classes:       3
Interface Bandwidth:           100000000 kbps
Policy Name:                   tc_pmap
VOQ Base:                      1264
Accounting Type:               Layer1 (Include Layer 1 encapsulation and above)
------------------------------------------------------------------------------
Level1 Class                             =   tc1
Egressq Queue ID                         =   1265 (LP queue)
Queue Max. BW.                           =   10063882 kbps (10 %)
Queue Min. BW.                           =   0 kbps (default)
Inverse Weight / Weight                  =   1 / (BWR not configured)
Guaranteed service rate                  =   10000000 kbps
TailDrop Threshold                       =   12517376 bytes / 10 ms (default)
WRED not configured for this class
 
Level1 Class                             =   tc035
Egressq Queue ID                         =   1264 (LP queue)
Queue Max. BW.                           =   1011732 kbps (1 %)
Queue Min. BW.                           =   0 kbps (default)
Inverse Weight / Weight                  =   1 / (BWR not configured)
Guaranteed service rate                  =   1000000 kbps
TailDrop Threshold                       =   1253376 bytes / 10 ms (default)
WRED not configured for this class
 
Level1 Class                             =   class-default
Queue Max. BW.                           =   no max (default)
Queue Min. BW.                           =   0 kbps (default)
Inverse Weight / Weight                  =   0 / (BWR not configured)

show policy-map interface bundle-Ether 44 output sample 

Bundle-Ether44 output: tc_pmap
 
Class tc1
  Classification statistics          (packets/bytes)     (rate - kbps)
    Matched             :              429444/53823648             0
    Transmitted         :              429444/53823648             0
    Total Dropped       :                   0/0                    0
  Queueing statistics
    Queue ID                             : None (Bundle)
    Taildropped(packets/bytes)           : 0/0
Class tc035
  Classification statistics          (packets/bytes)     (rate - kbps)
    Matched             :             1288331/161470820            0
    Transmitted         :             1288331/161470820            0
    Total Dropped       :                   0/0                    0
  Queueing statistics
    Queue ID                             : None (Bundle)
    Taildropped(packets/bytes)           : 0/0
Class class-default
  Classification statistics          (packets/bytes)     (rate - kbps)
    Matched             :                   0/0                    0
    Transmitted         :                   0/0                    0
    Total Dropped       :                   0/0                    0
  Queueing statistics
    Queue ID                             : None (Bundle)
    Taildropped(packets/bytes)           : 0/0
Policy Bag Stats time: 1557216940000  [Local Time: 05/07/19 08:15:40.000]
RP/0/RP0/CPU0:BB1#

Use Case

With the ingress traffic matching the same match criteria, you can group the egress traffic up to three unique TC mapped profiles. Using this feature, you can provide differentiated services to customers based on the SLAs they have signed up for.

In the example that follows, the ingress policy-map sets the ingress match criteria for the traffic class from 0 through 5. Based on the SLAs, you can group the TC values at the egress PM to deliver differentiated services.

After you group the TC values, you can apply specific egress actions under that class.

Ingress match:

class EXP1
  set traffic-class 1
!
class EXP2
  set traffic-class 2
!
class EXP3
  set traffic-class 3
!
class EXP4
  set traffic-class 4
!
class EXP5
  set traffic-class 5
!
class class-default
!
end-policy-map
!

Egress match:

Sample TC mapped class for policy-map PM1

class-map match-any TC2:1
match traffic-class 0 1
end-class-map

Sample TC mapped class for policy-map PM2

class-map match-any TC3:1
match traffic-class 0 1 2
end-class-map

Sample TC mapped class for policy-map PM3

class-map match-any TC6:1
match traffic-class 0 1 2 3 4 5
end-class-map

Configuring QoS Groups with an ACL

You can create QoS groups and configure ACLs to classify traffic into the groups based on a specified match condition. In this example, we match by the QoS group value (0-511).

Prerequisites

Before you can configure QoS groups with an ACL, the QoS peering profile must be enabled on the router or the line card. After enabling QoS peering, the router or line card must be reloaded, as shown in the following configuration.

Enabling QoS Peering Profile on the Router

Enter the global configuration mode and enable the QoS peering profile for the router as shown:

RP/0/RP0/CPU0:router(config)# hw-module profile qos ingress-model peering 
RP/0/RP0/CPU0:router(config)# exit
RP/0/RP0/CPU0:router# reload
Enabling QoS Peering Profile on the Line Card

Enter the global configuration mode and enable the QoS peering profile for the line card as shown:

RP/0/RP0/CPU0:router(config)# hw-module profile qos ingress-model peering location 0/0/CPU0
RP/0/RP0/CPU0:router(config)# exit
RP/0/RP0/CPU0:router# reload location 0/0/CPU0

Configuration

Use the following set of configuration statements to configure an ACL with QoS groups.


/*
 Enter the global configuration mode, and configure an ACL with the required QoS groups. */
RP/0/RP0/CPU0:router# configure
RP/0/RP0/CPU0:router(config)# ipv4 access-list qos-acl
RP/0/RP0/CPU0:router(config-ipv4-acl)# 10 permit ipv4 host 5.0.0.1 any set qos-group 1
RP/0/RP0/CPU0:router(config-ipv4-acl)# 11 permit ipv4 host 6.0.0.1 any set qos-group 2 
RP/0/RP0/CPU0:router(config-ipv4-acl)# 12 permit ipv4 host 7.0.0.1 any set qos-group 3
RP/0/RP0/CPU0:router(config-ipv4-acl)# 13 deny ipv4 any any


/* Create a policy map with the required classes.
In this example, we also create a default class for traffic that does not belong to any of the specified
classes. */
RP/0/RP0/CPU0:router(config)# policy-map qos-acl-map 
RP/0/RP0/CPU0:router(config-pmap)# class qos1
RP/0/RP0/CPU0:router(config-pmap-c)# set dscp af43
RP/0/RP0/CPU0:router(config-pmap-c)# set traffic-class 2
RP/0/RP0/CPU0:router(config-pmap-c)# exit

RP/0/RP0/CPU0:router(config-pmap)# class qos2
RP/0/RP0/CPU0:router(config-pmap-c)# set precedence critical
RP/0/RP0/CPU0:router(config-pmap-c)# set traffic-class 7
RP/0/RP0/CPU0:router(config-pmap-c)# exit

RP/0/RP0/CPU0:router(config-pmap)# class qos3
RP/0/RP0/CPU0:router(config-pmap-c)# set precedence 2
RP/0/RP0/CPU0:router(config-pmap-c)# set traffic-class 2
RP/0/RP0/CPU0:router(config-pmap-c)# exit 

RP/0/RP0/CPU0:router(config-pmap)# class qos4
RP/0/RP0/CPU0:router(config-pmap-c)# set traffic-class 4
RP/0/RP0/CPU0:router(config-pmap-c)# set dscp cs4
RP/0/RP0/CPU0:router(config-pmap-c)# exit

RP/0/RP0/CPU0:router(config-pmap)# class class-default 
RP/0/RP0/CPU0:router(config-pmap-c)# police rate percent 20
RP/0/RP0/CPU0:router(config-pmap-c-police)# exit


/* Create the class maps for specifying the match conditions. */
RP/0/RP0/CPU0:router(config)# class-map match-any qos1
RP/0/RP0/CPU0:router(config-cmap)# match qos-group 1
RP/0/RP0/CPU0:router(config-cmap)# end-class-map
 
RP/0/RP0/CPU0:router(config)# class-map match-any qos2
RP/0/RP0/CPU0:router(config-cmap)#  match qos-group 2
RP/0/RP0/CPU0:router(config-cmap)# end-class-map 

RP/0/RP0/CPU0:router(config)# class-map match-any qos3
RP/0/RP0/CPU0:router(config-cmap)# match qos-group 3
RP/0/RP0/CPU0:router(config-cmap)# end-class-map 

RP/0/RP0/CPU0:router(config)# class-map match-any qos4
RP/0/RP0/CPU0:router(config-cmap)# match qos-group 4
RP/0/RP0/CPU0:router(config-cmap)# end-class-map 


/* Apply the access list and the QoS map to the Gigabit interface, and commit your configuration. */
RP/0/RP0/CPU0:router(config)# interface TenGigE0/0/0/1
RP/0/RP0/CPU0:router(config-if)# ipv4 address 12.0.0.1/24
RP/0/RP0/CPU0:router(config-if)# no shut
RP/0/RP0/CPU0:router(config-if)# service-policy input qos-acl-map
RP/0/RP0/CPU0:router(config-if)# ipv4 access-group qos-acl ingress compress level 3

RP/0/RP0/CPU0:router(config-if)# commit             
Tue Mar 28 10:23:34.106 IST
 
RP/0/0/CPU0:Mar 28 10:37:48.570 : ifmgr[397]: %PKT_INFRA-LINK-3-UPDOWN : Interface TenGigE0/0/0/1, changed state to Down 
RP/0/0/CPU0:Mar 28 10:37:48.608 : ifmgr[397]: %PKT_INFRA-LINK-3-UPDOWN : Interface TenGigE0/0/0/1, changed state to Up 

RP/0/RP0/CPU0:router(config-if)# exit

Running Configuration

Confirm your configuration.

RP/0/RP0/CPU0:router(config)# show run
Tue Mar 28 10:37:55.737 IST

Building configuration...
!! IOS XR Configuration 0.0.0

ipv4 access-list qos-acl
10 permit ipv4 host 5.0.1.1 any set qos-group 1
11 permit ipv4 host 6.0.1.1 any set qos-group 2
12 permit ipv4 host 7.0.1.1 any set qos-group 3
13 deny ipv4 any any 
 
class-map match-any qos1
match qos-group 1
end-class-map
!
class-map match-any qos2
match qos-group 2
end-class-map
!
class-map match-any qos3
match qos-group 3
end-class-map
!
class-map match-any qos4
match qos-group 4
end-class-map
!
 
policy-map qos-acl-map
class qos1
  set dscp af43
  set traffic-class 2
!
class qos2
  set precedence critical
  set traffic-class 7
!
class qos3
  set precedence 2
  set traffic-class 2
!
class qos4
  set traffic-class 4
  set dscp cs4
!
class class-default
  police rate percent 20
  !
!
end-policy-map
!
 
interface TenGigE0/0/0/1
service-policy input qos-acl-map
ipv4 address 12.0.0.1 255.255.255.0
ipv4 access-group qos-acl ingress compress level 3

!

You have successfully configured an ACL with QoS groups.

Restrictions

Refer to the following table for Ingress QoS Scale limitation.

Table 1. Ingress QoS Scale Limitation

QoS Mode

Class-Map Size

Maximum number of Interfaces with Ingress QoS Applied
Per Core Per NPU

Normal

4

1023

2046

Normal

8

511

1022

Normal

16

255

510

Normal

32

127

254

Enhanced

4

871

1742

Enhanced

8

435

870

Enhanced

16

217

434

Enhanced

32

108

216

Note

If you apply an ingress policy map to a bundle that has bundle members only from a single core of an NPU, the QoS resources are consumed on both cores of that NPU.

Example: For Default Configuration, which is Normal (2 counter mode) QoS Mode & 32 Class Map-Size, you can configure 127 interfaces with Ingress Policy per core.

Other restrictions to follow:

  • If you have a set traffic class statement explicitly configured in ingress service policy, it is mandatory to have a corresponding match traffic class on egress for the traffic to be correctly matched and the stats to be accounted in show policy-map interface <> output command. To match the ingress traffic to egress class-default, traffic class should be set to 0 on ingress.

  • If you have a set traffic class that is configured in ingress service policy, and no corresponding match traffic class on egress, the traffic will not go to class default and the stats for this traffic flow will not be seen in show policy-map interface <> output command.

  • If you do not have any set traffic class statement in ingress, then traffic will hit the default-class on egress.

  • If you have a set discard-class statement configured in ingress service policy, it is mandatory to have a corresponding match discard-class on egress for the traffic to be correctly matched and the stats to be accounted in show policy-map interface <> output command.

  • If you have a set discard-class statement configured in ingress service policy and do not have a corresponding match discard-class on egress, the traffic will not hit the class-default and the stats for this flow will not be accounted in show policy-map interface <> output command.

  • The system does not support class-map size on peering mode.

  • Depending on the packet size, the traffic shaped value for low shaper rates, such as 10mbps, have greater deviation than 5% of tolerance from the shaper value. For higher shaper rates, the deviation is within the limit of 5% of tolerance from the shaper value for all packet sizes.

Restrictions for Peering QoS Profile

  • explicit set discard-class statement is not supported.

  • This feature is supported only on L3 interfaces and is limited to 1000 L3 interfaces per system.

  • set mpls exp topmost statement is not supported within QoS in peering mode.

  • access group statement is not supported.

  • (Only in Release 6.2.x and Release 6.3.x) set mpls exp imposition statement is not supported on ingress interface.

  • 2-Level ingress policer is not supported.

  • (From Release 6.5.x) Egress H-QOS with peering profile support is enabled, but ingress H-QOS with peering profile is not supported.

  • Depending on the packet size, the traffic shaped value for low shaper rates, such as 10mbps, have greater deviation than 5% of tolerance from the shaper value. For higher shaper rates, the deviation is within the limit of 5% of tolerance from the shaper value for all packet sizes.

Restrictions for QoS on BVI

  • The system does not support the egress policy on Bridge-Group Virtual Interface (BVI), but BVI (CoS, DEI) marking is supported by applying the policy to its corresponding Layer 2 interface, which is part of the same bridge domain.

  • If you apply L3 ingress QoS policy on L2 interface, which is a part of the same bridge-domain as BVI, the classification might not work if packets are destined to the BVI MAC address.

  • If a QoS policy is attached to BVI, the policy is inherited by the L2 interfaces, which are part of the same bridge-domain. Hence, any other policy cannot be applied on the L2 interfaces. Similarly, if a QoS policy is attached to any of the L2 interfaces, any QoS policy cannot be applied on the BVI, which is part of the same bridge-domain.

Restrictions for Egress Drop Action

  • A maximum of 8 interfaces can have the drop action configured and a maximum of 8 classes in any single policy can have the drop action.

  • A drop action in any particular class cannot be combined with other actions.

  • Drop action in a policy applied on the main interface is not inherited onto sub-interfaces.

  • Match condition for drop action PM can only based on qos-group, discard class based match is not supported.

In-Place Policy Modification

The In-Place policy modification feature allows you to modify a QoS policy even when the QoS policy is attached to one or more interfaces. A modified policy is subjected to the same checks that a new policy is subject to when it is bound to an interface. If the policy-modification is successful, the modified policy takes effect on all the interfaces to which the policy is attached. However, if the policy modification fails on any one of the interfaces, an automatic rollback is initiated to ensure that the pre-modification policy is in effect on all the interfaces.

You can also modify any class map used in the policy map. The changes made to the class map take effect on all the interfaces to which the policy is attached.


Note

  • The QoS statistics for the policy that is attached to an interface are lost (reset to 0) when the policy is modified.

  • When a QoS policy attached to an interface is modified, there might not be any policy in effect on the interfaces in which the modified policy is used for a short period of time.

  • The system does not support the show policy-map statistics for marking policies.

  • An in-place modification of an ACL does not reset the policy-map statistics counter.

Note

  • For QOS EXP-Egress marking applied on a Layer 3 interface on Cisco NCS550x and NCS55Ax routers, there is a limit of two unique policy-maps per NPU. This limit is three unique policy maps per NPU for routers that have the Cisco NC57 line cards installed. When the maximum limit for policy-maps is reached and you try to modify a policy-map which is shared between different interfaces, you may get an error.

  • For QOS egress marking (CoS, DEI) applied on a Layer 2 interface, there is a limit of 13 unique policy-maps per NPU. When the maximum limit for policy-maps is reached and you try to modify a policy-map which is shared between different interfaces, you may get an error.

Verification

If unrecoverable errors occur during in-place policy modification, the policy is put into an inconsistent state on target interfaces. No new configuration is possible until the configuration session is unblocked. It is recommended to remove the policy from the interface, check the modified policy and then re-apply accordingly.

References for Modular QoS Service Packet Classification

Specification of the CoS for a Packet with IP Precedence

Use of IP precedence allows you to specify the CoS for a packet. You can create differentiated service by setting precedence levels on incoming traffic and using them in combination with the QoS queuing features. So that, each subsequent network element can provide service based on the determined policy. IP precedence is usually deployed as close to the edge of the network or administrative domain as possible. This allows the rest of the core or backbone to implement QoS based on precedence.

Figure 2. IPv4 Packet Type of Service Field

You can use the three precedence bits in the type-of-service (ToS) field of the IPv4 header for this purpose. Using the ToS bits, you can define up to eight classes of service. Other features configured throughout the network can then use these bits to determine how to treat the packet in regard to the ToS to grant it. These other QoS features can assign appropriate traffic-handling policies, including congestion management strategy and bandwidth allocation. For example, queuing features such as LLQ can use the IP precedence setting of the packet to prioritize traffic.

IP Precedence Bits Used to Classify Packets

Use the three IP precedence bits in the ToS field of the IP header to specify the CoS assignment for each packet. You can partition traffic into a maximum of eight classes and then use policy maps to define network policies in terms of congestion handling and bandwidth allocation for each class.

Each precedence corresponds to a name. IP precedence bit settings 6 and 7 are reserved for network control information, such as routing updates. These names are defined in RFC 791.

IP Precedence Value Settings

By default, the routers leave the IP precedence value untouched. This preserves the precedence value set in the header and allows all internal network devices to provide service based on the IP precedence setting. This policy follows the standard approach stipulating that network traffic should be sorted into various types of service at the edge of the network and that those types of service should be implemented in the core of the network. Routers in the core of the network can then use the precedence bits to determine the order of transmission, the likelihood of packet drop, and so on.

Because traffic coming into your network can have the precedence set by outside devices, we recommend that you reset the precedence for all traffic entering your network. By controlling IP precedence settings, you prohibit users that have already set the IP precedence from acquiring better service for their traffic simply by setting a high precedence for all of their packets.

The class-based unconditional packet marking and LLQ features can use the IP precedence bits.

IP Precedence Compared to IP DSCP Marking

If you need to mark packets in your network and all your devices support IP DSCP marking, use the IP DSCP marking to mark your packets because the IP DSCP markings provide more unconditional packet marking options. If marking by IP DSCP is undesirable, however, or if you are unsure if the devices in your network support IP DSCP values, use the IP precedence value to mark your packets. The IP precedence value is likely to be supported by all devices in the network.

You can set up to 8 different IP precedence markings and 64 different IP DSCP markings.

Conditional Marking of MPLS Experimental bits for L3VPN Traffic

The conditional marking of MPLS experimental bits is achieved for Layer 3 Virtual Private Network (L3VPN) traffic by applying a combination of ingress and egress policy-maps on the Provider Edge (PE) router. In the ingress policy-map, the qos-group or discard-class is set either based on the result of the policing action or implicitly. The egress policy-map matches on qos-group or discard-class and sets the mpls experiment bits to the corresponding value.

This feature is supported on both IPv4 and IPv6 traffic in the L3VPN network. Conditional marking can be used to mark the MPLS experimental bits differently for in-contract and out-of-contract packets. In-contract packets are the confirmed packets with the color green and discard-class set to 0. Out-of-contract packets are the packets which have exceeded the limit and have the color yellow and discard-class set to 1.

Conditional marking of MPLS experimental bits for L3VPN traffic is supported on both physical and bundle main interfaces as well as sub-interfaces.

Restrictions for Conditional Marking of MPLS Experimental bits on L3VPN

  1. In the case of two PE routers connected back-to-back and the only label that the traffic between the routers have is the BGP label, then the explicit null label should be configured.

  2. A maximum of three policy-maps which perform conditional marking of MPLS experimental bits can be configured per Network Processor Unit (NPU) of the Cisco NCS 5500 Series Routers.

  3. In the ingress policy-map if qos-group is being set for the incoming traffic packets, then setting of dscp and mpls experimental bits will not work.

  4. Both the ingress and egress policy-maps must be applied in order to attain the expected behaviour. If either one of them is not applied then it may lead to undefined behaviour.

  5. If the egress policy-map does not match on qos-group or discard-class and set the mpls experiment bits to the required value, then the mpls experimental bits will be set to a value of zero, by default.

QoS DSCP Preservation

Table 2. Feature History Table

Feature Name

Release Information

Feature Description

The DSCP value of the packet is preserved only for L3VPN networks when the packets are destined to the directly connected routes on the PE routers. To preserve the DSCP value for packets to destinations beyond the egress PE routers for L3VPN, you should use the label mode per-vrf command under the VRF at the PE routers. Similarly for MPLS networks, the default behaviour is uniform mode where the penultimate hop copies the MPLS EXP bit to IP DSCP and IP DSCP value is not preserved beyond the egress PE router. To preserve the IP DSCP value, you should use the mpls ip-ttl-propagate disable command at the penultimate hop.

DSCP value preservation is not supported on NC55-24DD and NC55-18DD-SE line cards for Cisco IOS XR Release 7.0.2.

Policy-map for conditional marking of incoming IPv4 and IPv6 traffic

The incoming packets are classified based on the ingress policy-map and the following actions are done.

  • Set qos-group

  • Discard class or drop precedence is set implicitly or as a result of a policing action.

  • Packets that violate the configured policer are dropped in the ingress processing itself.

Running Configuration:

policy-map ingress
 class af11
  police rate percent 10 peak-rate percent 20 
  ! 
  set qos-group 1
 ! 
 class af22
  police rate percent 30 peak-rate percent 50 
  ! 
  set qos-group 2
 ! 
 class af32
  set qos-group 3
  police rate percent 30 peak-rate percent 60 
  ! 
 ! 
 class class-default
 ! 
 end-policy-map
!

Policy-map for conditional marking of outgoing MPLS traffic

The IPv4 or IPv6 ingress packet undergoes MPLS encapsulation during the egress processing in the PE router which performs the label imposition. The MPLS experimental bits are marked on the basis of egress policy-map which performs the following actions:

  • Match on qos-group or discard class or both

  • Set the MPLS experimental bits based on the match criteria

Running Configuration:

policy-map egress
 class qos1_disc0 # This class matches on qos-group 1 and discard-class 0
  set mpls experimental imposition 1
 ! 
 class qos1_disc1 # This class matches on qos-group 1 and discard-class 1
  set mpls experimental imposition 5
 ! 
 class qos2_disc0 # This class matches on qos-group 2 and discard-class 0
  set mpls experimental imposition 2
 ! 
 class qos2_disc1 # This class matches on qos-group 2 and discard-class 1
  set mpls experimental imposition 6
 ! 
 class qos3_disc0 # This class matches on qos-group 3 and discard-class 0
  set mpls experimental imposition 3
 ! 
 class qos3_disc1 # This class matches on qos-group 3 and discard-class 1
  set mpls experimental imposition 7
 ! 
 class class-default
 ! 
 end-policy-map
!

Conditional Marking of MPLS Experimental bits for L2VPN Traffic


Note

This feature is not available on NC55-24DD and NC55-18DD-SE line cards for Cisco IOS XR Release 7.0.2.

This feature is supported on Virtual Private Wire Service (VPWS), and Virtual Private LAN Service (VPLS) traffic in the L2VPN network, and currently not supported for Ethernet Virtual Private Network (EVPN).

The conditional marking of MPLS experimental bits is achieved for Layer 2 Virtual Private Network (L2VPN) traffic by applying a combination of ingress and egress policy-maps on the Provider Edge (PE) router. In the ingress policy-map, the qos-group or discard-class is set either based on the result of the policing action or implicitly. The egress policy-map matches on qos-group or on a combination of qos-group and discard-class and sets the mpls experiment bits to the corresponding value.

Conditional marking can be used to mark the MPLS experimental bits differently for in-contract and out-of-contract packets. In-contract packets are the confirmed packets with the color green and discard-class set to 0. Out-of-contract packets are the packets which have exceeded the limit and have the color yellow and discard-class set to 1.

Conditional marking of MPLS experimental bits for L2VPN traffic is supported on both physical and bundle main interfaces as well as sub-interfaces.

Restrictions for Conditional Marking of MPLS Experimental bits on L2VPN

  1. In the case of two PE routers connected back-to-back and the only label that the traffic between the routers have is the BGP label, then the explicit null label should be configured.


  2. A maximum of two policy-maps which perform conditional marking of MPLS experimental bits can be configured per Network Processor Unit (NPU) of the Cisco NCS 5500 Series Routers. However, the same policy can be applied on multiple interfaces on the same NPU.

  3. In the ingress policy-map if qos-group is being set for the incoming traffic packets, then setting of dscp and mpls experimental bits will not work.

  4. Both the ingress and egress policy-maps must be applied in order to attain the expected behaviour. If either one of them is not applied then it may lead to undefined behaviour.

  5. If the egress policy-map does not match on qos-group or discard-class and set the mpls experiment bits to the required value, then the mpls experimental bits will be set to a value of zero, by default.

Policy-map for conditional marking of incoming traffic

The incoming packets on the Power Edge router are classified based on the ingress policy-map and these actions are taken.

  • Set qos-group

  • Discard class or drop precedence is set implicitly or as a result of a policing action.

  • Set traffic class

  • Packets that violate the configured policer are dropped in the ingress processing itself.

Running Configuration:

class-map af11
   match cos 1
!

policy-map ingress
 class af11
  police rate percent 10 peak-rate percent 20 
  ! 
  set qos-group 1
  set Traffic-class 3
 ! 
 class class-default
 ! 
 end-policy-map
!

Policy-map for conditional marking of outgoing MPLS traffic

The ingress packet undergoes MPLS encapsulation during the egress processing in the PE router which performs the label imposition. The MPLS experimental bits are marked on the basis of egress policy-map which performs the following actions:

  • Match on qos-group or discard class or both

  • Set the MPLS experimental bits based on the match criteria

Running Configuration:

class-map match-all qos-group2_0
   match qos-group 2
   match discard-class 0

policy-map egress-marking
 class qos-group2_0 # This class matches on qos-group 2 and discard-class 0
  set mpls experimental imposition 1
 ! 
 class class-default
 ! 
 end-policy-map
! 
policy-map Egress-Queuing
 class Traffic-class3
  shape average 500 mbps
! 
 class class-default
!
end-policy-map
!

QPPB

QoS Policy Propagation via BGP (QPPB) is a mechanism that allows propagation of quality of service (QoS) policy and classification by the sending party that is based on the following:

  • Access lists

  • Community lists

  • Autonomous system paths in the Border Gateway Protocol (BGP)

Thus, helps in classification that is based on the destination address instead of the source address.

QoS policies that differentiate between different types of traffic are defined for a single enterprise network. For instance, one enterprise may want to treat important web traffic, not-important web traffic, and all other data traffic as three different classes. And thereafter, use the different classes for the voice and video traffic.

Hence, QPPB is introduced to overcome the following problems:

  • The administrative challenges of classifying that is based on ACLs.

  • The administrative problems of just listing the networks that need premium services.

QPPB allows marking of packets that are based on QoS group value associated with a Border Gateway Protocol (BGP) route.

Benefits of QPPB

  • QPPB provides an IP prefix-based QoS capability.

  • Traffic to IP addresses that have specific IP prefixes can be prioritized above other IP addresses.

  • IP prefixes of interest are tagged through the control plane that uses common BGP route-map techniques, including the community attribute.

  • Traffic to the tagged BGP prefixes is then classified and prioritized via the data forwarding plane by using the IOS-XR MQC (Modular QoS CLI) mechanisms, such as re-marking.

  • QPPB provides the glue between the BGP control plane and the IP data forwarding plane in support of IP prefix-based QoS.

  • BGP configuration within QPPB uses a table map to match specific prefixes learned through BGP neighbors, and then sets the router’s local QoS Group variable maintained within the Forwarding Information Base (FIB) for those specific prefixes.

  • The router supports a subset of full QPPB options - only IP destination prefix mode on input policy is supported.

Figure 3. Sample Scenario

Router A learns routes from AS 200 and AS 100. QoS policy is applied to any ingress interface of Router A to match the defined route maps with destination prefixes of incoming packets. Matching packets on Router A to AS 200 or AS 100 are sent with the appropriate QoS policy from Router A.

BGP maintains a scalable database of destination prefixes, QPPB, by using BGP table maps. BGP adds the ability to map a qos-group value to desired IP destinations. These qos-group values are used in QOS policies applied locally on ingress interfaces. Whenever a packet bound for such destinations is encountered, the qos-group value matching that destination route looks up with work inside the policy classmap, and marks that packet for any configured policy actions.

Configuration Workflow

Use the following configuration workflow for QPPB:

  • Define route policy.

  • Put Route policy at table-policy attach point under BGP.

  • Define classmaps and ingress policy to use the qos-groups that are used in table-policy.

  • Enable ipv4/ipv6 QPPB configuration under the desired interfaces.

  • Configure the QPPB hardware profile, hw-module profile qos ipv6 short.

  • If you use ipv6 QPPB, you must reload that linecard. If you use only ipv4 QPPB, linecard reload is not mandatory.

Define route policy

A routing policy instructs the router to inspect routes, filter them, and potentially modify their attributes as they are accepted from a peer, advertised to a peer, or redistributed from one routing protocol to another.

The routing policy language (RPL) provides a language to express routing policy. You must set up destination prefixes either to match inline values or one of a set of values in a prefix set.

Example:
prefix-set prefix-list-v4
    70.1.1.1,
    70.2.1.0/24,
    70.2.2.0/24 ge 28,
    70.2.3.0/24 le 28
end-set
prefix-set prefix-list-v6
    2001:300::2,
    2003:200::3
end-set
  
route-policy qppb1
    if destination in (60.60.0.2) then
        set qos-group 5
    elseif destination in prefix-list-v4 then
        set qos-group 4
    else
        set qos-group 1
     pass 
endif
end-policy

For NC57 line cards, the set qos-group value under the route policy for QPPB support is 0-15. Even though the set qos-group value option displays supported values <0-31> as show below, the configuration fails for any value above 15 for NC57 line cards. 

RP/0/RP0/CPU0:Fretta(config-rpl-if)#set qos-group ?
  <0-31>     decimal number

Put Route policy at table-policy attach point under BGP

The table-policy attach point permits the route policy to perform actions on each route as they are installed into the RIB routing table. QPPB uses this attachment point to intercept all routes as they are received from peers. Ultimately the RIB will update the FIB in the hardware forwarding plane to store destination prefix routing entries, and in cases where table policy matches a destination prefix, the qos-group value is also stored with the destination prefix entry for use in the forwarding plane.

Example:
router bgp 900
    [vrf <name>]
    bgp router-id 22.22.22.22
    address-family ipv4 unicast
        table-policy qppb1
    address-family ipv6 unicast
        table-policy qppb2
    neighbor 30.2.2.1 
        remote-as 500
        address-family ipv4 unicast   
            route-policy pass in
            route-policy pass out	
        address-family ipv6 unicast
            route-policy pass in
            route-policy pass out

Ingress interface QOS and ipv4/ipv6 bgp configuration

QPPB would be enabled per interface and individually for V4 and V6. An ingress policy would match on the qos groups marked by QPPB and take desired action.

If a packet is destined for a destination prefix on which BGP route policy has stored a qos-group, but it ingresses on an interface on which qppb is not enabled, it would not be remarked with qos-group.

Earlier, router supported matching on qos-group only in peering profile ‘hw-module profile qos ingress-model peering location <>’ . QPPB now permits classmaps to match qos-group in the default “non peering mode qos” as well. Also QPPB and hierarchical QOS policy profiles can work together if Hqos is used.

Example:
class-map match-any qos-group5
    match qos-group 5
    end-class-map
 
class-map match-any qos-group4
    match qos-group 4  
    end-class-map
  
policy-map ingress-marker-po1
    class qos-group5
        set precedence 0
        set discard-class 0 
        set traffic-class 1 
   
    class qos-group4
        set precedence 1
        set discard-class 1
        set traffic-class 2
    class class-default
   
end-policy-map

Configuring QPPB on an Interface

  1. RP/0/RP0/CPU0:router # configure

    Enters interface configuration mode and associates one or more interfaces to the VRF. 

  2. 
RP/0/RP0/CPU0:router(config)# interface 
type interface-path-id

    Enters interface configuration mode and associates one or more interfaces to the VRF.

  3. ipv4 | ipv6 bgp policy propagation inputqos-groupdestination

    Example:
    
RP/0/RP0/CPU0:router(config-if)# ipv4 bgp policy propagation input qos-group destination

    Enables QPPB on an interface

  4. commit

Egress Interface Configuration

The traffic-class set on ingress has no existence outside the device. Also, traffic-class is not a part of any packet header but is associated internal context data on relevant packets. It can be used as a match criteria in an egress policy to set up various fields on the outgoing packet or shape flows.

Restrictions:

  • No IP precedence marking.

  • No policing on egress policy.

class-map match-any level1
     match traffic-class 1
end-class-map

class-map match-any level2
    match traffic-class 2
end-class-map

policy-map output-po1
    class level1
        bandwidth percent 50
    class level2
        bandwidth percent 20
        queue-limit 50 ms
end-policy-map

interface hun 0/5/0/0
     ipv4 address 30.1.1.1/24
     ipv6 address 2001:da8:b0a:12f0::1/64
     service-policy output output-po1