Configuring QoS on Interfaces

This chapter contains the following sections:

Information About Interface QoS

Trust Boundaries

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.

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.

Policy for Fibre Channel Interfaces

The egress queues are not configurable for native Fibre Channel interfaces. Two queues are available as follows:

  • A strict priority queue to serve high-priority control traffic.

  • A queue to serve all data traffic and low-priority control traffic.

QoS for Multicast Traffic

By default, all multicast Ethernet traffic is classified into the default drop system class. This traffic is serviced by one multicast queue.

Optimized multicasting allows use of the unused multicast queues to achieve better throughput for multicast frames. If optimized multicast is enabled for the default drop system class, the system will use all 128 queues to service the multicast traffic. When optimized multicast is enabled for the default drop system class, all 128 queues are given equal priority.

If you define a new system class, a dedicated multicast queue is assigned to that class. This queue is removed from the set of queues available for the optimized multicast class.

The system provides two predefined class maps for matching broadcast or multicast traffic. These class maps are convenient for creating separate policy maps for unicast and multicast traffic.

The predefined class maps are as follows:

class-all-flood

The class-all-flood class map matches all broadcast, multicast, and unknown unicast traffic (across all CoS values). If you configure a policy map with the class-all-flood class map, the system automatically uses all available multicast queues for this traffic.

class-ip-multicast

The class-ip-multicast class map matches all IP multicast traffic. Policy options configured in this class map apply to traffic across all Ethernet CoS values. For example, if you enable optimized multicast for this class, the IP multicast traffic for all CoS values is optimized.


Note

If you configure either of these predefined class maps as a no-drop class, the priority flow control capability is applied across all Ethernet CoS values. In this configuration, pause will be applied to unicast and multicast traffic.

Configuring Interface QoS

Configuring Untagged CoS

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.

Procedure

  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)# untagged cos cos-value

Configures the untagged CoS value. Values can be from 1 to 7.

Example

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

Configuring an Interface Service Policy

An input qos policy is a service policy applied to incoming traffic on an Ethernet interface for classification. For type queuing, the output policy is applied to all outgoing traffic that matches the specified class.

Procedure

  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.

Note 

The service policy on a port channel applies to all member interfaces.

Step 3

switch(config-if)# service-policy input policy-name

Applies the policy map to the interface.

Note 

There is a restriction that system type qos policy cannot be the same as any the type qos policy applied to an interface or EtherChannel.

Example

This example shows how to apply a policy to an Ethernet interface: 

switch# configure terminal
switch(config)# interface ethernet 1/1
switch(config-if)# service-policy type qos input policy1

Configuring a Service Policy for a Layer 3 Interface

You can configure a service policy for a Layer 3 interface.

Procedure

  Command or Action Purpose
Step 1

switch# configure terminal

Enters global configuration mode.

Step 2

switch(config)# interface ethernet slot/port

Enters the configuration mode for the specified interface.

Step 3

switch(config-if)# no switchport

Selects the Layer 3 interface.

Example

The following example shows how to attach a queuing policy map to a Layer 3 interface: 

switch# configure terminal
switch(config)# interface ethernet 1/5
switch(config-if)# no switchport
switch(config-if)# service-policy type queuing output my_output_q_policy
switch(config-if)#

The following example shows how to attach an input qos policy map to a Layer 3 interface: 

switch# configure terminal
switch(config)# interface ethernet 1/5
switch(config-if)# no switchport
switch(config-if)# service-policy type qos input my_input_qos_policy
switch(config-if)#

Verifying the Interface QoS 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.

show policy-map interface [interface number]

Displays the policy map settings for an interface or all interfaces.

show queuing interface [interface slot/\port]

Displays the queue configuration and statistics.

show interface flowcontrol [module numbef ]

Displays the detailed listing of the flow control settings on all interfaces.

show interface [interface slot/port] priority-flow-control [module number]

Displays the priority flow control details for a specified interface.

show interface untagged-cos [module number]

Displays the untagged CoS values for all interfaces.

running-config ipqos

Displays information about the running configuration for QoS.

startup-config ipqos

Displays information about the startup configuration for QoS.