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This chapter contains the following sections:
The configurable Cisco NX-OS quality of service (QoS) features allow you to classify the network traffic, prioritize the traffic flow, and provide congestion avoidance.
The default QoS configuration on the device provides best-effort service for Ethernet traffic. QoS can be configured to provide additional classes of service for Ethernet traffic. Cisco NX-OS QoS features are configured using Cisco Modular QoS CLI (MQC).
In the event of congestion or collisions, Ethernet will drop packets. The higher level protocols detect the missing data and retransmit the dropped packets.
The Cisco Modular QoS CLI (MQC) provides a standard set of commands for configuring QoS.
You can use MQC to define additional traffic classes and to configure QoS policies for the whole system and for individual interfaces. Configuring a QoS policy with MQC consists of the following steps:
MQC provides two command types to define traffic classes and policies:
Defines a class map that represents a class of traffic based on packet-matching criteria. Class maps are referenced in policy maps.
The class map classifies incoming packets based on matching criteria, such as the IEEE 802.1p class of service (CoS) value. Unicast and multicast packets are classified.
Defines a policy map that represents a set of policies to be applied on a class-by-class basis to class maps.
The policy map defines a set of actions to take on the associated traffic class, such as limiting the bandwidth or dropping packets.
You define the following class-map and policy-map object types when you create them:
Defines MQC objects that you can use for system level related actions.
Defines MQC objects that you can use for classification.
Defines MQC objects that you can use for queuing and scheduling.
Note | The qos type is the default for the class-map and policy-map commands, but not for the service-policy which requires that you specify an explicit type. |
You can attach policies to interfaces or EtherChannels as well as at the global system level by using the service-policy command.
You can view all or individual values for MQC objects by using the show class-map and show policy-map commands.
An MQC target is an entity (such as an Ethernet interface) that represents a flow of packets. A service policy associates a policy map with an MQC target and specifies whether to apply the policy on incoming or outgoing packets. This mapping enables the configuration of QoS policies such as marking, bandwidth allocation, buffer allocation, and so on.
The system qos is a type of MQC target. You use a service policy to associate a policy map with the system qos target. A system qos policy applies to all interfaces on the switch unless a specific interface has an overriding service-policy configuration. The system qos policies are used to define system classes, the classes of traffic across the entire switch, and their attributes.
If service policies are configured at the interface level, the interface-level policy always takes precedence over system class configuration or defaults.
On the Cisco Nexus device, a system class is uniquely identified by a qos-group value. A total of eight system classes are supported. The device supports one default class which is always present on the switch. Up to seven additional system classes can be created by the administrator.
The device provides the drop system class.
By default, the software classifies all unicast and multicast Ethernet traffic into the default drop system class. This class is identified by qos-group 0.
This class is created automatically when the system starts up (the class is named class-default in the CLI). You cannot delete this class and you cannot change the match criteria associated with the default class.
The device supports a number of policy types. You create class maps in the policy types.
The following QoS parameters can be specified for each type of class:
Type network-qos—A network-qos policy is used to instantiate system classes and associate parameters with those classes that are of system-wide scope.
Classification—The traffic that matches this class are as follows:
Policy—The actions that are performed on the matching traffic are as follows:
Note | A network-qos policy can only be attached to the system QoS target. |
MTU—The MTU that needs to be enforced for the traffic that is mapped to a system class.
Note | The Cisco Nexus device supports one MTU for all classes for all ports. |
Set CoS value—This configuration is used to mark 802.1p values for all traffic mapped to this system class.
Note | Enabling ECN on a class on a network-qos policy implies that ECN is enabled for all ports in the system. |
Type queuing—A type queuing policy is used to define the scheduling characteristics of the queues associated with system classes.
The Cisco Nexus device supports type queuing in the egress direction.
Note | Some configuration parameters when applied to an EtherChannel are not reflected on the configuration of the member ports. |
Classification—The traffic that matches this class are as follows:
Policy—The actions that are performed on the matching traffic are as follows:
Note | These policies can be attached to the system qos target or to any interface. The output queuing policy is used to configure output queues on the device associated with system classes. |
Type qos—A type QoS policy is used to classify traffic that is based on various Layer 2, Layer 3, and Layer 4 fields in the frame and to map it to system classes.
Note | Some configuration parameters when applied to an EtherChannel are not reflected on the configuration of the member ports. |
Classification—The traffic that matches this class are as follows:
Access Control Lists—Classifies traffic based on the criteria in existing ACLs.
Class of Service—Matches traffic based on the CoS field in the frame header.
DSCP—Classifies traffic based on the Differentiated Services Code Point (DSCP) value in the DiffServ field of the IP header.
IP Real Time Protocol—Classifies traffic on the port numbers used by real-time applications.
Precedence—Classifies traffic based on the precedence value in the type of service (ToS) field of the IP header.
Policy—The actions that are performed on the matching traffic are as follows:
Note | This policy can be attached to the system or to any interface. It applies to input traffic only. |
A network-qos policy is used to instantiate system classes and associate parameters with those classes that are of system-wide scope.
Classification—The traffic that matches this class are as follows:
Note | A network-qos policy can only be attached to the system QoS target. |
MTU—The MTU that needs to be enforced for the traffic that is mapped to a system class.
Note | The Cisco Nexus device supports one MTU for all classes for all ports. |
Set CoS value—This configuration is used to mark 802.1p values for all traffic mapped to this system class.
Congestion Control DCTCP and ECN—Data Center TCP (DCTCP) is an enhancement to the TCP congestion control algorithm for data center networks. It leverages Explicit Congestion Notification (ECN) feature, to mark all the packets when the queue length exceeds a configured DCTCP threshold value. The routers and end hosts use this marking as a signal that the network is congested to slow down sending packets. To enable an DCTCP/ECN, use the "congestion-control dctcp ecn" command in the network-qos policy map mode.
Note | Enabling DCTCP and ECN on a class on a network-qos policy implies that DCTCP and ECN is enabled for all ports in the system. |
switch# configuration terminal Enter configuration commands, one per line. End with CNTL/Z. switch(config)# policy-map type network-qos system_network_policy switch(config-pmap-nq)# class type network-qos nc1 switch(config-pmap-nq-c)# set cos 2 switch(config-pmap-nq-c)# class type network-qos nc2 switch(config-pmap-nq-c)# congestion-control dctcp ecn-threshold 30000 bytes switch(config-pmap-nq-c)# switch(config-pmap-nq-c)# system qos switch(config-sys-qos)# service-policy type network-qos system_network_policy switch(config-sys-qos)# end switch# switch# show policy-map system Type network-qos policy-maps =============================== policy-map type network-qos system_network_policy class type network-qos nc1 match qos-group 1 mtu 1500 set cos 2 class type network-qos nc2 match qos-group 2 mtu 1500 congestion-control dctcp ecn-threshold 30000 bytes class type network-qos class-default match qos-group 0 mtu 1500
A queuing policy type is used to define the scheduling characteristics of the queues associated with system classes.
The Cisco Nexus device supports type queuing in the egress direction.
Note | Some configuration parameters when applied to a Port Channel are not reflected on the configuration of the member ports. |
Classification—The traffic that matches this class are as follows:
Policy—The actions that are performed on the matching traffic are as follows:
Note | These policies can be attached to the system qos target or to any interface. The output queuing policy is used to configure output queues on the device associated with system classes. |
A QoS policy type is used to classify traffic that is based on various Layer 2, Layer 3, and Layer 4 fields in the frame and to map it to system classes.
Note | Some configuration parameters when applied to a Port Channel are not reflected on the configuration of the member ports. |
Classification—The traffic that matches this class are as follows:
Access Control Lists—Classifies traffic based on the criteria in existing ACLs.
Class of Service—Matches traffic based on the CoS field in the frame header.
DSCP—Classifies traffic based on the Differentiated Services Code Point (DSCP) value in the DiffServ field of the IP header.
IP Real Time Protocol—Classifies traffic on the port numbers used by real-time applications.
Precedence—Classifies traffic based on the precedence value in the type of service (ToS) field of the IP header.
Policy—The actions that are performed on the matching traffic are as follows:
Note | This policy can be attached to the system or to any interface. It applies to input traffic only. |
The Cisco Nexus device supports one MTU for all classes for all ports.
When configuring MTU, follow these guidelines:
For the Cisco Nexus device, the MTU is controlled by the value configured on the class default.
Enter the system jumbomtu command to define the upper bound of any MTU in the system. The system jumbo MTU has a default value of 9216 bytes. The minimum MTU is 1500 bytes and the maximum MTU is 9216 bytes.
The system class MTU sets the MTU for all packets in the class. The system class MTU cannot be configured larger than the global jumbo MTU.
The default system class has a default MTU of 1500 bytes. You can configure this value.
You can specify the MTU value for either a single Layer 3 interface or a range of Layer 3 interfaces. When you change the Layer 3 interface MTU value to the jumbo MTU value (1500 bytes or greater), you must also change the network QoS MTU value to 1500 bytes or greater. The device generates a syslog message to inform you of this requirement.
The trust boundary is enforced by the incoming interface as follows:
By default, all Ethernet interfaces are trusted interfaces.The 802.1p CoS and DSCP are preserved unless the marking is configured. There is no default CoS to queue and DSCP to queue mapping. You can define and apply a policy to create these mappings. By default, without a user defined policy, all traffic is assigned to the default queue.
Any packet that is not tagged with an 802.1p CoS value is classified into the default drop system class. If the untagged packet is sent over a trunk, it is tagged with the default untagged CoS value, which is zero.
You can override the default untagged CoS value for an Ethernet interface or port channel.
You can override the default untagged CoS value for an Ethernet interface or a port channel interface using the untagged cos cos-value command.
You can override the default untagged Cos value for an Ethernet or a Layer 3 interface or a port channel interface using the untagged cos cos-value command.
After the system applies the untagged CoS value, QoS functions the same as for a packet that entered the system tagged with the CoS value.
You use classification to partition traffic into classes. You classify the traffic based on the packet property (CoS field) or the packet header fields that include IP precedence, Differentiated Services Code Point (DSCP), and Layer 2 to Layer 4 parameters. The values used to classify traffic are called match criteria.
Traffic that fails to match any class is assigned to a default class of traffic called class-default.
You can associate an egress policy map with an Ethernet interface to guarantee the bandwidth for the specified traffic class or to configure the egress queues.
Each Ethernet interface supports up to five queues, one for each system class. The queues have the following default configuration:
In addition to these queues, control traffic that is destined for the CPU uses strict priority queues. These queues are not accessible for user configuration.
Standard Ethernet traffic in the default drop system class is assigned a queue. This queue uses WRR scheduling with 100 percent of the bandwidth.
If you add a system class, a queue is assigned to the class. You must reconfigure the bandwidth allocation on all affected interfaces. Bandwidth is not dedicated automatically to user-defined system classes.
You can configure one strict priority queue. This queue is serviced before all other queues except the control traffic queue (which carries control rather than data traffic).
The device automatically applies QoS policies to traffic that is directed to the CPU to ensure that the CPU is not flooded with packets. Control traffic, such as bridge protocol data units (BPDU) frames, is given higher priority to ensure delivery.
To maintain optimal switch performance, follow these guidelines when configuring system classes and policies:
Switch resources (such as buffers, virtual output queues, and egress queues) are partitioned based on the default and user-defined system classes. Cisco NX-OS automatically adjusts the resource allocation to accommodate the configured system classes.
When configuring Port Channels, the service policy configured on an Port Channel applies to all member interfaces.
By default, queues 6 and 7 are reserved for control plane traffic and queue 5 for SPAN traffic. So you can configure four classes along with the default class.
Some streams experience buffer crunch as the competing streams use up all the system buffers. There is no fair distribution of the shared buffers on Cisco Nexus N3548 Series switches, due to which the streams that can not be buffered are dropped aggressively. This results in the output rates that are less than the configured bandwidth for that stream and the other streams that exceed the configured bandwidth.
To work around this issue, you have to configure the CLI command hardware profile buffer qos-group X threshold Y where X is the qos-group number of the traffic that is exceeding the configured bandwidth and Y is the percentage of the shared buffers that can be used by the stream. The threshold value Y should be a small value, for example, 10 or 20. It can be fine tuned based on the burst absorption rate that is required at the same time honoring the bandwidth. The default threshold is 95%.
Configuring System Classes
You can create or modify a class map with the class-map command. The class map is a named object that represents a class of traffic. In the class map, you specify a set of match criteria for classifying the packets. You can then reference class maps in policy maps.
Note | The class map type default is type qos and its match criteria default is match-all. |
You can classify traffic by matching packets based on an existing access control list (ACL). Traffic is classified by the criteria defined in the ACL. The permit and deny ACL keywords are ignored in the matching; even if a match criteria in the access-list has a deny action, it is still used for matching for this class.
Command or Action | Purpose | |||
---|---|---|---|---|
Step 1 |
switch#
configure terminal
|
Enters global configuration mode. | ||
Step 2 |
switch(config)#
class-map type qos
class-name
|
Creates a named object that represents a class of traffic. Class-map names can contain alphabetic, hyphen, or underscore characters, are case sensitive, and can be up to 40 characters. | ||
Step 3 |
switch(config-cmap-qos)#
match access-group
name
acl-name
|
Configures a traffic class by matching packets based on the acl-name. The permit and deny ACL keywords are ignored in the matching.
| ||
Step 4 |
switch(config-cmap-qos)#
no match access-group
name
acl-name
| (Optional)
Removes the match from the traffic class. |
This example shows how to classify traffic by matching packets based on existing ACLs:
switch# configure terminal
switch(config)# class-map type qos class_acl
switch(config-cmap-qos)# match access-group name acl-01
Use the show class-map command to display the ACL class-map configuration:
switch# show class-map class_acl
You can classify traffic based on the class of service (CoS) in the IEEE 802.1Q header. This 3-bit field is defined in IEEE 802.1p to support QoS traffic classes. CoS is encoded in the high order 3 bits of the VLAN ID Tag field and is referred to as user_priority.
Command or Action | Purpose | |
---|---|---|
Step 1 |
switch#
configure terminal
|
Enters global configuration mode. |
Step 2 |
switch(config)#
class-map type qos
class-name
|
Creates a named object that represents a class of traffic. Class-map names can contain alphabetic, hyphen, or underscore characters, are case sensitive, and can be up to 40 characters. |
Step 3 |
switch(config-cmap-qos)#
match cos
cos-value
|
Specifies the CoS value to match for classifying packets into this class. You can configure a CoS value in the range of 0 to 7. |
Step 4 |
switch(config-cmap-qos)#
no match cos
cos-value
| (Optional)
Removes the match from the traffic class. |
This example shows how to classify traffic by matching packets based on a defined CoS value:
switch# configure terminal switch(config)# class-map type qos match-any class_cos switch(config-cmap-qos)# match cos 4, 5-6
Use the show class-map command to display the CoS value class-map configuration:
switch# show class-map class_cos
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 |
AF32 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 |
Command or Action | Purpose | |
---|---|---|
Step 1 | switch# configure terminal |
Enters global configuration mode. |
Step 2 |
switch(config)#
class-map type qos
class-name
|
Creates a named object that represents a class of traffic. Class-map names can contain alphabetic, hyphen, or underscore characters, are case sensitive, and can be up to 40 characters. |
Step 3 |
switch(config-cmap-qos)#
match dscp
dscp-list
|
Configures the traffic class by matching packets based on the values in the dscp-list variable. For a list of DSCP values, see the Standard DSCP Values table. |
Step 4 |
switch(config-cmap-qos)#
no match dscp
dscp-list
| (Optional)
Removes the match from the traffic class. For a list of DSCP values, see the Standard DSCP Values table. |
This example shows how to classify traffic by matching packets based on the DSCP value in the DiffServ field of the IP header:
switch# configure terminal switch(config)# class-map type qos match-any class_dscp switch(config-cmap-qos)# match dscp af21, af32Use the show class-map command to display the DSCP class-map configuration:
switch# show class-map class_dscp
The IP Real-time Transport Protocol (RTP) is a transport protocol for real-time applications that transmits data such as audio or video and is defined by RFC 3550. Although RTP does not use a common TCP or UDP port, you typically configure RTP to use ports 16384 to 32767. UDP communications use an even port and the next higher odd port is used for RTP Control Protocol (RTCP) communications.
You can classify based on UDP port ranges, which are likely to target applications using RTP.
Command or Action | Purpose | |
---|---|---|
Step 1 |
switch#
configure terminal
|
Enters global configuration mode. |
Step 2 |
switch(config)#
class-map type qos
class-name
|
Creates a named object that represents a class of traffic. Class-map names can contain alphabetic, hyphen, or underscore characters, are case sensitive, and can be up to 40 characters. |
Step 3 |
switch(config-cmap-qos)#
match ip rtp
port-number
|
Configures the traffic class by matching packets based on a range of lower and upper UDP port numbers, which is likely to target applications using RTP. Values can range from 2000 to 65535. |
Step 4 |
switch(config-cmap-qos)#
no match ip rtp
port-number
| (Optional)
Removes the match from the traffic class. |
switch# configure terminal switch(config)# class-map type qos match-any class_rtp switch(config-cmap-qos)# match ip rtp 2000-2100, 4000-4100
Use the show class-map command to display the RTP class-map configuration:
switch# show class-map class_rtp
You can classify traffic based on the precedence value in the type of service (ToS) byte field of the IP header. The following table shows the 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) |
Command or Action | Purpose | |
---|---|---|
Step 1 | switch# configure terminal |
Enters global configuration mode. |
Step 2 | switch(config)# class-map type qos match-any class-name |
Creates a named object that represents a class of traffic. Class-map names can contain alphabetic, hyphen, or underscore characters, are case sensitive, and can be up to 40 characters. |
Step 3 | switch(config-cmap-qos)#match precedence precedence-values |
Configures the traffic class by matching packets based on precedence values. For a list of precedence values, see the Precedence Values table. |
Step 4 | switch((config-cmap-qos)# no match precedence precedence-values | (Optional)
Removes the match from the traffic class. For a list of precedence values, see the Precedence Values table. |
This example shows how to classify traffic by matching packets based on the precedence value in the ToS byte field of the IP header:
switch# configure terminal switch(config)# class-map type qos match-any class_precedence switch(config-cmap-qos)# match precedence 1-2, critical
Use the show class-map command to display the IP precedence value class-map configuration:
switch# show class-map class_precedence
The policy-map command is used to create a named object that represents a set of policies that are to be applied to a set of traffic classes.
The device provides one default system class: a drop class for best-effort service (class-default). You can define up to four additional system classes for Ethernet traffic.
The following predefined policy maps are used as default service policies:
You need to create a policy map to specify the policies for any user-defined class. In the policy map, you can configure the QoS parameters for each class. You can use the same policy map to modify the configuration of the default classes.
The device distributes all the policy-map configuration values to the attached network adapters.
Before creating the policy map, define a class map for each new system class.
Command or Action | Purpose | |||
---|---|---|---|---|
Step 1 |
switch#
configure
terminal
|
Enters global configuration mode. | ||
Step 2 |
switch(config)#
policy-map [type {network-qos |
qos |
queuing}]
policy-name
|
Creates a named object representing a set of policies that are to be applied to a set of traffic classes. Policy-map names can contain alphabetic, hyphen, or underscore characters, are case sensitive, and can be up to 40 characters. The three policy-map configuration modes are as follows: | ||
Step 3 |
switch(config)#
no
policy-map [type {network-qos |
qos |
queuing}]
policy-name
| (Optional)
Deletes the specified policy map. | ||
Step 4 |
switch(config-pmap)#
class
[type {network-qos |
qos |
queuing}]
class-name
|
Associates a class map with the policy map, and enters configuration mode for the specified system class. The three class-map configuration modes are as follows:
| ||
Step 5 |
switch(config-pmap)#
no
class [type {network-qos |
qos
|
queuing}]
class-name
| (Optional)
Deletes the class map association. |
Type qos policies are used for classifying the traffic of a specific system class identified by a unique qos-group value. A type qos policy can be attached to the system or to individual interfaces for ingress traffic only.
You can set a maximum of five QoS groups for ingress traffic.
Command or Action | Purpose | |||
---|---|---|---|---|
Step 1 | switch# configure terminal |
Enters global configuration mode. | ||
Step 2 | switch(config)# policy-map type qos policy-name |
Creates a named object that represents a set of policies that are to be applied to a set of traffic classes. Policy-map names can contain alphabetic, hyphen, or underscore characters, are case sensitive, and can be up to 40 characters. | ||
Step 3 | switch(config-pmap-qos)# [class | class-default] type qos class-name |
Associates a class map with the policy map, and enters configuration mode for the specified system class.
| ||
Step 4 | switch(config-pmap-c-qos)# set qos-group qos-group-value |
Configures one or more qos-group values to match on for classification of traffic into this class map. The list below identifies the ranges of the qos-group-value . There is no default value.
| ||
Step 5 | switch(config-pmap-c-qos)# no set qos-group qos-group-value | (Optional)
Removes the qos-group values from this class. |
This example shows how to define a type qos policy map:
switch# configure terminal switch(config)# policy-map type qos policy-s1 switch(config-pmap-qos)# class type qos class-s1 switch(config-pmap-c-qos)# set qos-group 2
Type network qos policies can only be configured on the system qos attachment point. They are applied to the entire switch for a particular class.
Command or Action | Purpose | |||
---|---|---|---|---|
Step 1 |
switch#
configure terminal
|
Enters configuration mode. | ||
Step 2 |
switch(config)#
policy-map type
network-qos
policy-name
|
Creates a named object that represents a set of policies that are to be applied to a set of traffic classes. Policy-map names can contain alphabetic, hyphen, or underscore characters, are case sensitive, and can be up to 40 characters. | ||
Step 3 |
switch(config-pmap-nq)#
class type network-qos
class-name
|
Associates a class map with the policy map, and enters configuration mode for the specified system class.
| ||
Step 4 |
switch(config-pmap-c-nq)#
mtu
mtu-value
|
Specifies the MTU value in bytes.
| ||
Step 5 |
switch(config-pmap-c-nq)#
no mtu
| (Optional)
Resets the MTU value in this class. | ||
Step 6 |
switch(config-pmap-c-nq)#
set cos
cos-value
|
Specifies a 802.1Q CoS value which is used to mark packets on this interface. The value range is from 0 to 7. | ||
Step 7 |
switch(config-pmap-c-nq)#
no set cos
cos-value
| (Optional)
Disables the marking operation in this class. |
This example shows how to define a type network-qos policy map:
switch# configure terminal switch(config)# policy-map type network-qos policy-que1 switch(config-pmap-nq)# class type network-qos class-que1 switch(config-pmap-c-nq)# mtu 5000 switch(config-pmap-c-nq)# set cos 4
Type queuing policies are used for scheduling and buffering the traffic of a specific system class. A type queuing policy is identified by its QoS group and can be attached to the system or to individual interfaces for input or output traffic.
Command or Action | Purpose | |||
---|---|---|---|---|
Step 1 | switch# configure terminal |
Enters global configuration mode. | ||
Step 2 |
switch(config)#
policy-map
type queuing
policy-name
|
Creates a named object that represents a set of policies that are to be applied to a set of traffic classes. Policy-map names can contain alphabetic, hyphen, or underscore characters, are case sensitive, and can be up to 40 characters. | ||
Step 3 |
switch(config-pmap-que)#
class type
queuing
class-name
|
Associates a class map with the policy map, and enters configuration mode for the specified system class. | ||
Step 4 |
switch(config-pmap-c-que)#
priority
|
Specifies that traffic in this class is mapped to a strict priority queue.
| ||
Step 5 |
switch(config-pmap-c-que)#
no
priority
| (Optional)
Removes the strict priority queuing from the traffic in this class. | ||
Step 6 |
switch(config-pmap-c-que)#
bandwidth
percent
percentage
|
| ||
Step 7 |
switch(config-pmap-c-que)#
no bandwidth
percent
percentage
| (Optional)
Removes the bandwidth specification from this class. |
(config-pmap-c-que)# queue-limit 0 bytes class type queuing cos-dscp-6 queue-limit 0 bytes class type queuing cos-dscp-7
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:
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.
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.
|
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 60, in addition to the standard DSCP values shown in the table below:
Note | You can set DSCP or IP precedence but you cannot set both values because they modify the same field in the IP packet. |
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 |
Command or Action | Purpose | |
---|---|---|
Step 1 | configure terminal |
Enters global configuration mode. |
Step 2 |
policy-map type qos qos-policy-map-name
|
Creates or accesses the policy map named qos-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. |
This example shows how to display the policy-map configuration as shown below:
switch# show policy-map policy1
You can set the value of the IP precedence field in bits 0 to 2 of the IPv4 type of service (ToS) field. The following table shows the precedence values:
Note | You can set IP precedence or DSCP but you cannot set both values because they modify the same field in the IP packet. |
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) |
Command or Action | Purpose | |
---|---|---|
Step 1 | switch# config terminal |
Enters global configuration mode. |
Step 2 |
switch(config) # 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 |
switch(config-pmap-nq) # 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 |
switch(config-pmap-c-nq) # 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. |
This example shows how to set the precedence marking to 5:
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)#
The service-policy command specifies the system class policy map as the service policy for the system.
Command or Action | Purpose | |||
---|---|---|---|---|
Step 1 | switch# configure terminal |
Enters global configuration mode. | ||
Step 2 |
switch(config)#
system
qos
|
Enters system class configuration mode. | ||
Step 3 |
switch(config-sys-qos)#
service-policy
type
{network-qos |
qos
input
|queuing [input |
output]}
policy-name
|
Specifies the policy map to use as the service policy for the system. There are three policy-map configuration modes:
|
If you have created and attached new policies to the system QoS configuration, enter the no form of the command to reapply the default policies.
Command or Action | Purpose | |
---|---|---|
Step 1 | switch# configure terminal |
Enters global configuration mode. |
Step 2 |
switch(config)#
system
qos
|
Enters system class configuration mode. |
Step 3 |
switch(config-sys-qos)#
no
service-policy type qos input
policy-map
name
|
Resets the classification mode policy map. This policy-map configuration is for system QoS input or interface input only: |
Step 4 |
switch(config-sys-qos)#
no
service-policy type network-qos
policy-map
name
|
Resets the network-wide policy map. |
Step 5 |
switch(config-sys-qos)#
no
service-policy type queuing
[input |
output]policy-map
name
|
Resets the output queuing mode policy map. |
You can enable the jumbo Maximum Transmission Unit (MTU) for the whole switch by setting the MTU to its maximum size (9216 bytes) in the policy map for the default Ethernet system class (class-default).
When you configure jumbo MTU on a port-channel subinterface you must first enable MTU 9216 on the base interface and then configure it again on the subinterface. If you enable the jumbo MTU on the subinterface before you enable it on the base interface then the following error will be displayed on the console:
switch(config)# int po 502.4 switch(config-subif)# mtu 9216 ERROR: Incompatible MTU values
Note | The Cisco Nexus device supports 1 MTU for all classes for all ports. |
To use FCoE on switch, add class-fcoe in the custom network-qos policy. If already using FCoE, make sure to add the below lines in the config so that the FCoE does not go down on the switch after enabling the jumbo qos policy.
switch# conf t switch(config)# policy-map type network-qos jumbo switch(config-pmap-nq)# class type network-qos class-fcoe switch(config-pmap-nq-c)# end
This example shows how to change qos to enable the jumbo MTU:
switch# conf t switch(config)# policy-map type network-qos jumbo switch(config-pmap-nq)# class type network-qos class-default switch(config-pmap-c-nq)# mtu 9216
Note | The system jumbomtu command defines the maximum MTU size for the switch. However, jumbo MTU is supported only for system classes that have MTU configured. |
On the Cisco Nexus device, traffic is classified into one of eight QoS groups. The MTU is configured at the QoS group level. By default, all Ethernet traffic is in QoS group 0. To verify the jumbo MTU for Ethernet traffic, use the show queueing interface ethernet slot/chassis_number command and find "HW MTU" in the command output to check the MTU for QoS group 0. The value should be 9216.
The show interface command always displays 1500 as the MTU. Because the Cisco Nexus device supports different MTUs for different QoS groups, it is not possible to represent the MTU as one value on a per interface level.
switch(config)# show queuing interface ethernet 1/19 Ethernet1/19 queuing information: TX Queuing qos-group sched-type oper-bandwidth 0 WRR 100 RX Queuing Multicast statistics: Mcast pkts dropped : 0 Unicast statistics: qos-group 0 HW MTU: 9216 (9216 configured) drop-type: drop, xon: 0, xoff: 0 Statistics: Ucast pkts dropped : 0
Configuring QoS on Interfaces
Any incoming packet not tagged with an 802.1p CoS value is assigned the default untagged CoS value of zero (which maps to the default Ethernet drop system class). You can override the default untagged CoS value for an Ethernet or EtherChannel interface.
You can configure flow control on a Layer 2 or Layer 3 interface. Use the no switchport command to configure a Layer 3 interface
Command or Action | Purpose | |
---|---|---|
Step 1 | switch# configure terminal |
Enters global configuration mode. |
Step 2 |
switch(config)#
interface {ethernet [chassis/]slot/port |
port-channel
channel-number}
|
Enters the configuration mode for the specified interface or port channel. |
Step 3 |
switch(config-if)#
no switchport
| (Optional)
Selects a Layer 3 interface. |
Step 4 |
switch(config-if)#
untagged cos
cos-value
|
Configures the untagged CoS value. Values can be from 1 to 7. |
The following example shows how to set the CoS value to 4 for untagged frames received on an interface:
switch# configure terminal switch(config)# interface ethernet 1/2 switch(config-if)# untagged cos 4
The following example shows how to set the CoS value to 3 for untagged frames received on a Layer 3 interface:
switch# configure terminal switch(config)# interface ethernet 1/5 switch(config-if) no switchport switch(config-if)# untagged cos 3 switch(config-if)#
Configuring Buffers and Queues
When you have a combination of 10-gigabyte and 1-gigabyte ports, you can use this command on the 1-gigabyte port to reduce the effects of the 1-gigabyte port blocking the 10-gigabyte port. Use this command on the 1-gigabyte port only when there is Head-of-Line Blocking (HOLB) on the 10-gigabyte port due to a slow receiver on the 1-gigabyte port.
Command or Action | Purpose | |||
---|---|---|---|---|
Step 1 | switch# configure terminal |
Enters global configuration mode. | ||
Step 2 | switch(config)# hardware profile multicast slow-receiver port port port-number} |
| ||
Step 3 | switch(config)# copy running-config startup-config | (Optional)
Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration. |
The following example shows how to configure port 46 as the multicast slow-receiver port:
switch# configure terminal switch(config)# hardware profile multicast slow-receiver port 46 switch(config)# copy running-config startup-config
You can configure the percentage of shared buffer used for a specific QoS group or virtual lane (VL)
Command or Action | Purpose | |
---|---|---|
Step 1 | switch# configure terminal |
Enters global configuration mode. |
Step 2 | switch# hardware profile buffer qosgroup number threshold percentage |
Configures the buffer for the specified QoS group. The number argument specifies the QoS group number. The range is from 0 to 4. The percentage argument specified the percentage of maximum usages. The range is from 1 to 100. |
Step 3 | switch(config)# copy running-config startup-config | (Optional)
Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration. |
The following example shows how to configure the shared buffer for QoS group 1 to a maximum of 40 percent usage:
switch# configure terminal switch(config)# hardware profile buffer qosgroup 1 threshold 40 switch(config)# copy running-config startup-config
You can configure the percentage of shared buffer used for SPAN traffic.
Command or Action | Purpose | |
---|---|---|
Step 1 | switch# configure terminal |
Enters global configuration mode. |
Step 2 | switch# hardware buffer span-threshold percentage |
Configures the percentage of maximum usage of the hardware buffer for SPAN traffic. The percentage range is from 0 to 100. |
Step 3 | switch(config)# copy running-config startup-config | (Optional)
Saves the change persistently through reboots and restarts by copying the running configuration to the startup configuration. |
The following example shows how to configure 30 percent of the hardware buffer for SPAN traffic:
switch# configure terminal switch(config)# hardware buffer span-threshold 30 switch(config)# copy running-config startup-config
To verify the QoS configurations, perform one of these tasks:
Command |
Purpose |
---|---|
switch# show class-map |
Displays the class maps defined on the device. |
switch# show policy-map [name] |
Displays the policy maps defined on the device. Optionally, you can display the named policy only. |
switch# show policy-map interface [interface number] |
Displays the policy map settings for an interface or all interfaces. |
switch# show policy-map system |
Displays the policy map settings attached to the system qos. |
switch# show policy-map type {network-qos | qos | queuing} [name] | Displays the policy map settings for a specific policy type. Optionally, you can display the named policy only. |
switch# show interface untagged-cos [ module number] | Displays the untagged CoS values for all interfaces. |
switch# show wrr-queue cos-map [var] | Displays the mapped CoS values to egress queues. |
switch# running-config ipqos | Displays information about the running configuration for QoS. |
switch# startup-config ipqos | Displays information about the startup configuration for QoS. |
switch# show queuing interface ethernet slot-no/port-no | Displays the queuing information on interfaces. |
This example shows how to configure a network QoS policy:
switch(config)# class-map type network-qos cnq1 switch(config-cmap-nq)# match qos-group 1 switch(config-cmap-nq)# exit switch(config)# class-map type network-qos cnq6 switch(config-cmap-nq)# match qos-group 6 switch(config-cmap-nq)# switch(config-cmap-nq)# exit switch(config)# policy-map type network-qos pnqos switch(config-pmap-nq)# class type network-qos cnq1 switch(config-pmap-nq-c)# set cos 4 switch(config-pmap-nq-c)# exit switch(config-pmap-nq)# class type network-qos cnq6 switch(config-pmap-nq-c)# set cos 5 switch(config-pmap-nq-c)# congestion-control random-detect ecn switch(config-pmap-nq-c)# exit switch(config-pmap-nq)# class type network-qos class-default switch(config-pmap-nq-c)# mtu 9216 switch(config-pmap-nq-c)# exit switch(config-pmap-nq)# exit switch(config)# system qos switch(config-sys-qos)# service-policy type network-qos pnqos switch(config-sys-qos)#
This example shows how to configure a queuing policy:
switch(config)# class-map type queuing cqu1 switch(config-cmap-que)# match qos-group 1 switch(config-cmap-que)# exit switch(config)# class-map type queuing cqu6 switch(config-cmap-que)# match qos-group 6 switch(config-cmap-que)# exit switch(config)# policy-map type queuing pqu switch(config-pmap-que)# class type queuing class-default switch(config-pmap-c-que)# bandwidth percent 70 switch(config-pmap-c-que)# exit switch(config-pmap-que)# class type queuing cqu1 switch(config-pmap-c-que)# bandwidth percent 10 switch(config-pmap-c-que)# exit switch(config-pmap-que)# class type queuing cqu6 switch(config-pmap-c-que)# bandwidth percent 20 switch(config-pmap-c-que)# exit switch(config-pmap-que)# exit switch(config)# system qos switch(config-sys-qos)# service-policy type queuing output pqu switch(config-sys-qos)#
This example shows how to configure a QoS policy:
switch(config)# class-map type qos cqos1 switch(config-cmap-qos)# match cos 1 switch(config-cmap-qos)# exit switch(config)# class-map type qos cqos6 switch(config-cmap-qos)# match cos 6 switch(config-cmap-qos)# exit switch(config)# policy-map type qos pqos switch(config-pmap-qos)# class type qos cqos1 switch(config-pmap-c-qos)# set qos-group 1 switch(config-pmap-c-qos)# exit switch(config-pmap-qos)# class type qos cqos6 switch(config-pmap-c-qos)# set qos-group 6 switch(config-pmap-c-qos)# exit switch(config-pmap-qos)# exit switch(config)# system qos switch(config-sys-qos)# service-policy type qos input pqos switch(config-sys-qos)#
This example shows how to verify the untagged-cos configuration on interfaces:
switch(config-if)# show interface untagged-cos ================================= Interface Untagged-CoS ================================= Ethernet1/1 4 Ethernet1/2 Ethernet1/3 5 Ethernet1/4 Ethernet1/5 Ethernet1/6 Ethernet1/7 Ethernet1/8 Ethernet1/9 Ethernet1/10 Ethernet1/11 Ethernet1/12 Ethernet1/13 Ethernet1/14 Ethernet1/15 Ethernet1/16 Ethernet1/17
This example shows how to display the QoS running configuration:
switch(config)# show running-config ipqos !Command: show running-config ipqos !Time: Mon Mar 15 08:24:12 2010 version 5.0(3)U1(1) class-map type qos match-all cqos1 match cos 1 class-map type qos match-all cqos6 match cos 6 class-map type queuing cqu1 match qos-group 1 class-map type queuing cqu6 match qos-group 6 policy-map type qos pqos class cqos1 set qos-group 1 class cqos6 set qos-group 6 policy-map type queuing pqu class type queuing cqu1 bandwidth percent 10 class type queuing cqu6 bandwidth percent 20 class type queuing class-default bandwidth percent 70 class-map type network-qos cnq1 match qos-group 1 class-map type network-qos cnq6 match qos-group 6 policy-map type network-qos pnqos class type network-qos cnq1 set cos 4 class type network-qos cnq6 set cos 5 congestion-control random-detect ecn class type network-qos class-default mtu 9216 system qos service-policy type qos input pqos service-policy type network-qos pnqos service-policy type queuing output pqu interface Ethernet1/1 untagged cos 4 interface Ethernet1/3 untagged cos 5 switch(config)#
This example shows how to display the class map configuration:
switch(config)# show class-map Type qos class-maps =================== class-map type qos match-all cqos1 match cos 1 class-map type qos match-all cqos6 match cos 6 class-map type qos match-any class-default match any Type queuing class-maps ======================= class-map type queuing cqu1 match qos-group 1 class-map type queuing cqu6 match qos-group 6 class-map type queuing class-default match qos-group 0 Type network-qos class-maps ============================== class-map type network-qos cnq1 match qos-group 1 class-map type network-qos cnq6 match qos-group 6 class-map type network-qos class-default match qos-group 0 switch(config)#
This example shows how to display the policy map configuration:
switch(config)# show policy-map Type qos policy-maps ==================== policy-map type qos pqos class type qos cqos1 set qos-group 1 class type qos cqos6 set qos-group 6 class type qos class-default set qos-group 0 policy-map type qos default-in-policy class type qos class-default set qos-group 0 Type queuing policy-maps ======================== policy-map type queuing pqu class type queuing cqu1 bandwidth percent 10 class type queuing cqu6 bandwidth percent 20 class type queuing class-default bandwidth percent 70 policy-map type queuing default-out-policy class type queuing class-default bandwidth percent 100 Type network-qos policy-maps =============================== policy-map type network-qos pnqos class type network-qos cnq1 mtu 1500 set cos 4 class type network-qos cnq6 mtu 1500 set cos 5 congestion-control random-detect ecn class type network-qos class-default mtu 9216 policy-map type network-qos default-nq-policy class type network-qos class-default mtu 1500 switch(config)#
This example shows how to display all active policy maps in the system:
switch(config)# show policy-map system Type network-qos policy-maps =============================== policy-map type network-qos pnqos class type network-qos cnq1 match qos-group 1 mtu 1500 set cos 4 class type network-qos cnq6 match qos-group 6 mtu 1500 set cos 5 congestion-control random-detect ecn class type network-qos class-default match qos-group 0 mtu 9216 Service-policy (qos) input: pqos policy statistics status: disabled Class-map (qos): cqos1 (match-all) Match: cos 1 set qos-group 1 Class-map (qos): cqos6 (match-all) Match: cos 6 set qos-group 6 Class-map (qos): class-default (match-any) Match: any set qos-group 0 Service-policy (queuing) output: pqu policy statistics status: disabled Class-map (queuing): cqu1 (match-any) Match: qos-group 1 bandwidth percent 10 Class-map (queuing): cqu6 (match-any) Match: qos-group 6 bandwidth percent 20 Class-map (queuing): class-default (match-any) Match: qos-group 0 bandwidth percent 70 switch(config)#
This example shows how to display the service policy maps configured on the interfaces:
switch(config)# show policy-map interface ethernet 1/1 Global statistics status : disabled Ethernet1/1 Service-policy (qos) input: pqos policy statistics status: disabled Class-map (qos): cqos1 (match-all) Match: cos 1 set qos-group 1 Class-map (qos): cqos6 (match-all) Match: cos 6 set qos-group 6 Class-map (qos): class-default (match-any) Match: any set qos-group 0 Service-policy (queuing) output: pqu policy statistics status: disabled Class-map (queuing): cqu1 (match-any) Match: qos-group 1 bandwidth percent 10 Class-map (queuing): cqu6 (match-any) Match: qos-group 6 bandwidth percent 20 Class-map (queuing): class-default (match-any) Match: qos-group 0 bandwidth percent 70 switch(config)#
switch(config)# show queuing interface ethernet 1/1 Ethernet1/1 queuing information: TX Queuing qos-group sched-type oper-bandwidth 0 WRR 20 1 WRR 10 2 WRR 10 3 WRR 10 4 WRR 10 RX Queuing Multicast statistics: Mcast pkts dropped : 0 Unicast statistics: qos-group 0 HW MTU: 1500 (1500 configured) drop-type: drop, xon: 0, xoff: 0 Statistics: Ucast pkts dropped : 0 qos-group 1 HW MTU: 1500 (1500 configured) drop-type: drop, xon: 0, xoff: 0 Statistics: Ucast pkts dropped : 0 qos-group 2 HW MTU: 1500 (1500 configured) drop-type: drop, xon: 0, xoff: 0 Statistics: Ucast pkts dropped : 0 qos-group 3 HW MTU: 1500 (1500 configured) drop-type: drop, xon: 0, xoff: 0 Statistics: Ucast pkts dropped : 0 qos-group 4 HW MTU: 1500 (1500 configured) drop-type: drop, xon: 0, xoff: 0 Statistics: Ucast pkts dropped : 0