QoS-MQC Support for MTR

QoS-MQC Support for MTR

Last Updated: July 23, 2010

The QoS-MQC Support for MTR feature enables Multitopology Routing (MTR) traffic classification. Traffic classification is used to associate different classes of traffic with different topologies when multiple topologies are configured on the same device. This module describes how to configure quality of service (QoS) with modular QoS CLI (MQC) support for MTR.

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Prerequisites for QoS-MQC Support for MTR

  • Be familiar with the concepts documented in the "MTR Traffic Classification" section.
  • Define a topology globally rather than at the interface level as in quality of service (QoS) before configuring traffic classification
  • Ensure that all devices throughout the network have the same definition of classifiers and the same sequencing of classifiers.
  • Carefully coordinate simultaneous configuration in a network where Multitopology Routing (MTR) and QoS traffic classification are configured.

Restrictions for QoS-MQC Support for MTR

  • Multitopology Routing (MTR) classification values must be unique for each topology. An error message is generated if you attempt to configure overlapping values.
  • A topology cannot be placed in the shutdown state if it is referenced by any active policy map.
  • A subset of differentiated services code point (DSCP) bits is used to encode classification values in the IP packet header. Certain DSCP values are reserved. These DSCP values are commonly used by routing software components for purposes unrelated to MTR (for example, Open Shortest Path First [OSPF], Bidirection Forwarding Detection [BFD], and Simple Network Management Protocol [SNMP]). If you use these values for MTR classification, they are likely to interfere with correct operation of the device and is strongly discouraged. These DSCP values are:
    • DSCP 16 (cs2)
    • DSCP 48 (cs6)

Information About QoS-MQC Support for MTR

MTR Traffic Classification

MTR cannot be enabled on a router until traffic classification is configured, even if only one class-specific topology is configured. Traffic classification is used to configure topology specific forwarding behaviors when multiple topologies are configured on the same router. Traffic classification must be applied consistently throughout the network. Class-specific packets are associated with the corresponding topology table forwarding entries.

Traffic classification is configured by using the Modular QoS CLI (MQC). MTR traffic classification is similar to QoS traffic classification. However, there is an important distinction. MTR traffic classification is defined globally for each topology, rather than at the interface level as in QoS.

A subset of DSCP bits is used to encode classification values in the IP packet header. You configure a class map to define the traffic class by entering the class-map command in global configuration mode. Only the match-any keyword is supported for MTR. You associate the traffic class with a policy by configuring the policy-map type class-routing ipv4 unicast command in global configuration mode. You activate the policy for the topology by configuring the service-policy type class-routing command in global address family configuration mode. When configured, the service policy is associated with all interfaces on the router.

Some of the same goals can be achieved through QoS configuration, to which MTR provides a more powerful and flexible alternative.You can configure MTR traffic classification and IP Differentiated Services or IP Precedence-based traffic classification in the same network. However, MTR requires exclusive use of some subset of the DSCP bits in the IP packet header for specific topology traffic. In a network where MTR and QoS traffic classification are configured, simultaneous configuration must be carefully coordinated.

For detailed steps, see the Configuring MTR Traffic Classification section.

How to Configure QoS-MQC Support for MTR

Configuring MTR Traffic Classification

Before You Begin

Note


Following the correct order of the commands in this task is very important. Ensure that all configuration that affects traffic classification is complete before entering the service-policy type class-routing command.
  • Be familiar with the concepts documented in the MTR Traffic Classification section.
  • Define a topology globally (rather than at the interface level as in QoS) before configuring traffic classification
  • Ensure that all routers throughout the network have the same definition of classifiers and the same sequencing of classifiers.
  • Carefully coordinate simultaneous configuration In a network where MTR and QoS traffic classification are configured.

Note


  • MTR classification values must be unique for each topology. An error message is generated if you attempt to configure overlapping values.
  • A topology cannot be placed in the shutdown state if it is referenced by any active policy map.
  • A subset of DSCP bits is used to encode classification values in the IP packet header. Certain DSCP values are reserved. These DSCP values are commonly used by routing software components for purposes unrelated to MTR (for example, OSPF, BFD, and/or SNMP). Using these values for MTR classification is likely to interfere with correct operation of the router and is strongly discouraged. These values include:
    • DSCP 48 (cs6)
    • DSCP 16 (cs2)


SUMMARY STEPS

1.    enable

2.    configure terminal

3.    class-map match-any class-map-name

4.    match [ip] dscp [dscp-value dscp-value dscp-value dscp-value dscp-value dscp-value dscp-valuedscp-value]

5.    exit

6.    policy-map type class-routing ipv4 unicast policy-map-name

7.    class {class-name | class-default}

8.    select-topology topology-name

9.    exit

10.    exit

11.    global-address-family ipv4 [multicast | unicast]

12.    service-policy type class-routing policy-map-name

13.    end

14.    show topology detail

15.    show policy-map type class-routing ipv4 unicast [interface [interface-type interface-number]]

16.    show mtm table


DETAILED STEPS
 Command or ActionPurpose
Step 1
enable


Example:

Router> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Router# configure terminal

 

Enters global configuration mode.

 
Step 3
class-map match-any class-map-name


Example:

Router(config)# class-map match-any VOICE-CLASS

 

Creates a class map to be used for matching packets to a specified class and enters class-map configuration mode.

  • The MTR traffic class is defined using this command.
Note    The match-any keyword must be entered when configuring classification for MTR.
 
Step 4
match [ip] dscp [dscp-value dscp-value dscp-value dscp-value dscp-value dscp-value dscp-valuedscp-value]


Example:

Router(config-cmap)# match ip dscp 9

 

Identifies a DSCP value as a match criteria.

  • Use the dcsp-value argument to define a specific metric value.
  • Do not use the DSCP values 48 and 16. See the Restrictions section for more information.
 
Step 5
exit


Example:

Router(config-cmap)# exit

 

Exits class-map configuration mode.

 
Step 6
policy-map type class-routing ipv4 unicast policy-map-name


Example:

Router(config)# policy-map type class-routing ipv4 unicast VOICE-CLASS-POLICY

 

Creates or modifies a policy map that can be attached to one or more interfaces to specify a service policy and enters policy-map configuration mode.

  • If you do not specify the type keyword option, the command defaults to the QoS policy.
 
Step 7
class {class-name | class-default}


Example:

Router(config-pmap)# class VOICE-CLASS

 

Specifies the name of the class whose policy you want to create or change or specifies the default class and enters policy-map class configuration mode.

  • The class map is referenced.
  • For a class map to be referenced in a class-routing policy map, it must first be defined by the class-map command as shown in Step 3.
 
Step 8
select-topology topology-name


Example:

Router(config-pmap-c)# select-topology VOICE

 

Attaches the policy map to the topology.

 
Step 9
exit


Example:

Router(config-pmap-c)# exit

 

Exits policy-map class configuration mode.

 
Step 10
exit


Example:

Router(config-pmap)# exit

 

Exits policy-map configuration mode.

 
Step 11
global-address-family ipv4 [multicast | unicast]


Example:

Router(config)# global-address-family ipv4

 

Enters global address family configuration mode to configure MTR.

 
Step 12
service-policy type class-routing policy-map-name


Example:

Router(config-af)# service-policy type class-routing VOICE-CLASS-POLICY

 

Attaches the service policy to the policy map for MTR traffic classification and activates MTR.

  • The policy-map-name argument must match that configured in step 6.
Note    After this command is entered, traffic classification is enabled. Ensure that all configuration that affects traffic classification is complete before entering this important command.
 
Step 13
end


Example:

Router(config-af)# end

 

Exits global address family configuration mode and returns to privileged EXEC mode.

 
Step 14
show topology detail


Example:

Router# show topology detail

 

(Optional) Displays detailed information about class-specific and base topologies.

 
Step 15
show policy-map type class-routing ipv4 unicast [interface [interface-type interface-number]]


Example:

Router# show policy-map type class-routing ipv4 unicast

 

(Optional) Displays the class-routing policy map configuration.

  • If you specify the interface keyword without the argument, statistics on all interfaces under the global space are displayed.
 
Step 16
show mtm table


Example:

Router# show mtm table

 

(Optional) Displays information about the DSCP values assigned to each topology.

 

Configuration Examples for QoS-MQC Support for MTR

Examples MTR Traffic Classification

The following example shows how to configure classification and activate MTR for two topologies:

global-address-family ipv4 
 topology VOICE 
  all-interfaces
  exit
 topology VIDEO 
  forward-base 
  maximum routes 1000 90 
  exit
 exit
class-map match-any VOICE-CLASS
 match ip dscp 9
 exit
class-map match-any VIDEO-CLASS
 match ip dscp af11
 exit
policy-map type class-routing ipv4 unicast MTR
 class VOICE-CLASS
  select-topology VOICE 
  exit
 class VIDEO-CLASS
  select-topology VIDEO
  exit 
 exit
global-address-family ipv4
 service-policy type class-routing MTR 
end 

The following example shows how to display detailed information about the VOICE and VIDEO topologies:

Router# show topology detail
Topology: base
  Address-family: ipv4
  Associated VPN VRF is default
  Topology state is UP
  Associated interfaces:
    Ethernet0/0, operation state: UP
    Ethernet0/1, operation state: DOWN
    Ethernet0/2, operation state: DOWN
    Ethernet0/3, operation state: DOWN 
    Loopback0, operation state: UP
          
Topology: VIDEO
  Address-family: ipv4
  Associated VPN VRF is default
  Topology state is UP
  Topology fallback is enabled
  Topology maximum route limit 1000, warning limit 90% (900)
  Associated interfaces:
Topology: VOICE
  Address-family: ipv4
  Associated VPN VRF is default
  Topology state is UP
  Topology is enabled on all interfaces
  Associated interfaces:
    Ethernet0/0, operation state: UP
    Ethernet0/1, operation state: DOWN
    Ethernet0/2, operation state: DOWN
    Ethernet0/3, operation state: DOWN
    Loopback0, operation state: UP
Topology: base
  Address-family: ipv4 multicast
  Associated VPN VRF is default
  Topology state is DOWN
  Multicast multi-topology mode is enabled.
  Route Replication Enabled:
    from unicast topology VOICE all route-map BLUE
  Associated interfaces:
    Ethernet0/0, operation state: UP
    Ethernet0/1, operation state: DOWN
    Ethernet0/2, operation state: DOWN
    Ethernet0/3, operation state: DOWN
    Loopback0, operation state: UP

The following example shows how to display the classification values for the VOICE and VIDEO topologies:

Router# show mtm table
 
MTM Table for VRF: default, ID:0
Topology                Address Family   Associated VRF         Topo-ID
base                    ipv4              default                 0       
VOICE                    ipv4             default                 2051    
Classifier: ClassID:3
DSCP: cs1 
DSCP: 9 
VIDEO                    ipv4             default                 2054    
Classifier: ClassID:4
DSCP: af11 

Additional References

Related Documents

Related Topic Document Title

Cisco IOS commands

Cisco IOS Master Command List, All Releases

Multitopology Routing (MTR) commands

Cisco IOS Multitopology Routing Command Reference

QoS commands

Cisco IOS Quality of Service Solutions Command Reference

QoS concepts and tasks

Quality of Service Solutions Configuration Guide Library

Technical Assistance

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Feature Information for QoS-MQC Support for MTR

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Table 1Feature Information for QoS-MQC Support for MTR
Feature Name Releases Feature Information

QoS-MQC Support for MTR

12.2(33)SRB

15.0(1)S

This feature enables Multitopology Routing (MTR) traffic classification. Traffic classification is used to associate different classes of traffic with different topologies when multiple topologies are configured on the same device. A subset of differentiated services code point (DSCP) bits is used to encode classification values in the IP packet header and mark the packet for classification. When MTR traffic classification is enabled, MTR is activated and ready for the routing protocols to start contributing to the topologies.

The following commands were introduced or modified: policy-map type class-routing ipv4 unicast, select topology, service-policy type class-routing, show mtm table, show policy-map type class-routing ipv4 unicast.

Glossary

base topology--The entire network for which the usual set of routes are calculated. This topology is the same as the default global routing table that exists without Multitopology Routing (MTR) being used.

class-specific topology--New topologies that are defined over and above the existing base topology; each class-specific topology is represented by its own Routing Information Base (RIB) and Forwarding Information Base (FIB).

classification--Selection and matching of traffic that needs to be provided with a different treatment based on its mark. Classification is a read-only operation.

DSCP--differentiated services code point. Six bits in the Type of Service (ToS) field. Two bits are used for Explicit Congestion Notification, which are used to mark the packet.

incremental forwarding mode--Incremental forwarding mode is designed to support transitional or incremental deployment of MTR, where devices are in the network that are not MTR enabled. In this mode, the device looks for a forwarding entry first in the class-specific FIB. If an entry is not found, the device then looks for the longest match in the base topology FIB. If an entry is found in the base topology FIB, the packet is forwarded on the base topology. If a forwarding entry is not found in the base topology FIB, the packet is dropped.

marking--Setting a value in the packet or frame. Marking is a read and write operation.

multitopology--Multitopology means that each topology routes and forward a subset of the traffic as defined by the classification criteria.

NLRI--Network Layer Reachability Information.

strict forwarding mode--Strict forwarding mode is the default forwarding mode for MTR. Only routes in the topology-specific routing table are considered. Among these, the longest match for the destination address is used. If no route containing the destination address can be found in the topology specific table, the packet is dropped.

TID--Topology Identifier. Each topology is configured with a unique topology ID. The topology ID is configured under the routing protocol and is used to identify and group NLRI for each topology in updates for a given protocol.

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