Cisco Nexus 5500 Series NX-OS Quality of Service Configuration Guide, Release 7.x

Information About Marking

Marking is a method that you use to modify the QoS fields of the incoming and outgoing packets.

You can use marking commands in traffic classes that are referenced in a policy map. The marking features that you can configure are listed below:

DSCP
IP precedence
CoS

Configuring DSCP Marking

For Cisco Nexus devices, you can set the DSCP value in the six most significant bits of the DiffServ field of the IP header to a specified value. You can enter numeric values from 0 to 63, in addition to the standard DSCP values shown in the table below:

Note

You can set DSCP or IP Precedence but you can not set both values because they modify the same field in the IP packet.

Table 1. Standard DSCP Values
Value	List of DSCP Values
af11	AF11 dscp (001010)—decimal value 10
af12	AF12 dscp (001100)—decimal value 12
af13	AF13 dscp (001110)—decimal value 14
af21	AF21 dscp (010010)—decimal value 18
af22	AF22 dscp (010100)—decimal value 20
af23	AF23 dscp (010110)—decimal value 22
af31	AF31 dscp (011010)—decimal value 26
af32	AF40 dscp (011100)—decimal value 28
af33	AF33 dscp (011110)—decimal value 30
af41	AF41 dscp (100010)—decimal value 34
af42	AF42 dscp (100100)—decimal value 36
af43	AF43 dscp (100110)—decimal value 38
cs1	CS1 (precedence 1) dscp (001000)—decimal value 8
cs2	CS2 (precedence 2) dscp (010000)—decimal value 16
cs3	CS3 (precedence 3) dscp (011000)—decimal value 24
cs4	CS4 (precedence 4) dscp (100000)—decimal value 32
cs5	CS5 (precedence 5) dscp (101000)—decimal value 40
cs6	CS6 (precedence 6) dscp (110000)—decimal value 48
cs7	CS7 (precedence 7) dscp (111000)—decimal value 56
default	Default dscp (000000)—decimal value 0
ef	EF dscp (101110)—decimal value 46

Procedure

	Command or Action	Purpose
Step 1	config t	Enters configuration mode.
Step 2	policy-map type qos `qos-policy-map-name`	Creates or accesses the policy map named policy-map-name, and then enters policy-map mode. The policy-map name can contain alphabetic, hyphen, or underscore characters, is case sensitive, and can be up to 40 characters.
Step 3	class [type qos] {`class-map-name` \| class-default}	Creates a reference to class-map-name, and enters policy-map class configuration mode. Use the class-default keyword to select all traffic that is not currently matched by classes in the policy map.
Step 4	set dscp `dscp-value`	Sets the DSCP value to dscp-value. See the Standards DSCP Values table.
Step 5	set qos-group `y`	Specifies the qos-group. The group value can be from 1 to 5.

Example

This example shows how to set the DSCP value to 10 and specify the qos-group to 2.

 policy-map type qos test-bulkdata
    class type qos bulkdata
      set dscp 10
      set qos-group 2

Configuring IP Precedence Marking

You can set the value of the IP precedence field in bits 0 to 2 of the IPv4 type of service (ToS) field or the equivalent Traffic Class field for IPv6 of the IP header. The following table shows the precedence values:

Note

You can set IP Precedence or DSCP but you can not set both values because they modify the same field in the IP packet.

Table 2. Precedence Values
Value	List of Precedence Values
<0-7>	IP precedence value
critical	Critical precedence (5)
flash	Flash precedence (3)
flash-override	Flash override precedence (4)
immediate	Immediate precedence (2)
internet	Internetwork control precedence (6)
network	Network control precedence (7)
priority	Priority precedence (1)
routine	Routine precedence (0)

Procedure

	Command or Action	Purpose
Step 1	config t	Enters configuration mode.
Step 2	policy-map [type qos] `qos-policy-map-name`	Creates or accesses the policy map named policy-map-name, and then enters policy-map mode. The policy-map name can contain alphabetic, hyphen, or underscore characters, is case sensitive, and can be up to 40 characters.
Step 3	class [type qos] {`class-map-name` \| class-default}	Creates a reference to class-map-name, and enters policy-map class configuration mode. Use the class-default keyword to select all traffic that is not currently matched by classes in the policy map.
Step 4	set precedence `precedence-value`	Sets the IP precedence value to precedence-value. You can enter one of the values shown in the Precedence Values table.

Example

switch(config)# policy-map type qos my_policy
switch(config-pmap-qos)# class type qos my_class
switch(config-pmap-c-qos)# set precedence 5
switch(config-pmap-c-qos)#

Configuring CoS Marking

The value of the CoS field is recorded in the high-order three bits of the VLAN ID Tag field in the IEEE 802.1Q header.

Procedure

Command or Action

Purpose

Step 1

switch# configure terminal

Enters global configuration mode.

Step 2

switch(config) # policy-map [type network-qos] policy-map name

Creates or accesses the policy map named policy-map-name and enters policy-map mode.

The policy-map name can contain alphabetic, hyphen, or underscore characters, is case sensitive, and can be up to 40 characters.

Step 3

switch(config-pmap-nq) # class [type network-qos] {class-map name |class-default}

Creates a reference to the class-map-name and enters policy-map class configuration mode.

Use the class-default keyword to select all traffic that is not currently matched by classes in the policy map.

Step 4

switch(config-pmap-c-nq) # set cos cos-value

Specifies the CoS value to cos-value.

The cos-value can range from 0 to 7.

Note

This command is supported only for egress policies.

Layer 3 QoS Characteristics

QoS Layer 3 characteristics are as follows:

Router-on-a-stick hardware architecture.
Classification carried through the Layer 3 ASIC via the dot1p header only.
Qos-group classification information at ingress interfaces lost in transit for routable traffic.

Note

The default Layer 2 CoS Mappings are not copied into the Layer 3 header. A policy is required to statically copy the CoS values into the 802.1p header.

QoS Recommendations:

Following are the QoS configuration recommendations:

Configure a 'type qos' policy and in the 'network-qos policy' do 'set cos'.
Apply type qos to Layer 2 interfaces, or Layer 3 interfaces or system wide (not SVI).
Apply this egress queuing policy system wide.
Pre-routed Traffic to Layer 3 engine is prioritized accordingly.
Post routing, the dot1p information in association with the network-qos policy is used to regenerate qos-group and direct it to a specific queue.
Layer 3 ASIC maps frames to a CoS queue based on the dot1p information (there are 8 CoS queues, so each CoS gets its queue).
The post routed traffic is scheduled according to the egress queuing policy.

Required CoS Marking Configuration in a Layer 3 Topology

In Layer 3 topologies, you must configure each QoS group in the network-qos policy with a unique cos value.

Procedure

Command or Action

Purpose

Step 1

switch# show policy-map system

Displays the already configured policy maps and CoS values.

In Layer 3 topologies, each qosgroup must have a unique CoS value. Use the show policy-map system command to view CoS values that have been used and that are unavailable for QoS groups.

Step 2

switch# configure terminal

Enters global configuration mode.

Step 3

switch(config) # policy-map [type network-qos] policy-map name

Creates or accesses the policy map named policy-map-name and enters policy-map mode.

The policy-map name can contain alphabetic, hyphen, or underscore characters, is case sensitive, and can be up to 40 characters.

Step 4

switch(config-pmap-nq) # class [type network-qos] {class-map name |class-default}

Creates a reference to the class-map-name and enters policy-map class configuration mode.

Use the class-default keyword to select all traffic that is not currently matched by classes in the policy map.

Step 5

switch(config-pmap-nq-c) # set cos cos-value

Specifies the CoS value.

The value can range from 0 to 7.

Note

You can use this command only in egress policies.

In Layer 3 topologies, each qos-group must have a unique cos configuration.

Example

This example shows how to set the CoS value to 4 in a Layer 3 topology:

switch# show policy-map system
  Type network-qos policy-maps
  ===============================
 
  policy-map type network-qos pn-01
    class type network-qos cn-01      match qos-group 1
      mtu 8500
      pause no-drop 
      set cos 2
    class type network-qos cn-02      match qos-group 2
      set cos 4
      mtu 9216
    class type network-qos cn-03      match qos-group 3 
      mtu 8000
      set cos 6
    class type network-qos cn-04      match qos-group 4 
      mtu 8750
      set cos 7
    class type network-qos cn-ip-multicast      match qos-group 5
      set cos 5
      mtu 7500
    class type network-qos class-default      match qos-group 0 
      mtu 1500
      set cos 1
...
switch# configure terminal 
switch(config)# policy-map type network-qos pn-01 
switch(config-pmap-nq)# class type network-qos cn-05 
switch(config-pmap-c-nq)# set cos 3

Verifying the Marking Configuration

Use one of the following commands to verify the configuration:


Command	Purpose
show class-map	Displays the class maps defined on the switch.
show policy-map [`name`]	Displays the policy maps defined on the switch. Optionally, you can display the named policy only.
running-config ipqos	Displays information about the running configuration for QoS.
startup-config ipqos	Displays informationa bout the startup configuration for QoS.

Bias-Free Language

Book Title

Cisco Nexus 5500 Series NX-OS Quality of Service Configuration Guide, Release 7.x

Chapter Title

Configuring Marking

Results

Chapter: Configuring Marking

Configuring Marking

Information About Marking

Configuring DSCP Marking

Procedure

Example

Configuring IP Precedence Marking

Procedure

Example

Configuring CoS Marking

Procedure

Layer 3 QoS Characteristics

QoS Recommendations:

Required CoS Marking Configuration in a Layer 3 Topology

Procedure

Example

Verifying the Marking Configuration

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