Catalyst 4500 Series Switch Cisco IOS Software Configuration Guide, 12.2(20)EWA

Configuring QoS

This chapter describes how to configure quality of service (QoS) by using automatic QoS (auto-QoS) commands or by using standard QoS commands on a Catalyst 4500 series switch. It also provides guidelines, procedures, and configuration examples.

This chapter consists of these sections:

•Overview of QoS

•Configuring Auto-QoS

•Configuring QoS

Note For complete syntax and usage information for the switch commands used in this chapter, first look at the Cisco Catalyst 4500 Series Switch Command Reference and related publications at this location:

http://www.cisco.com/en/US/products//hw/switches/ps4324/index.html

If the command is not found in the Catalyst 4500 Command Reference, it will be found in the larger Cisco IOS library. Refer to the Catalyst 4500 Series Switch Cisco IOS Command Reference and related publications at this location:

http://www.cisco.com/en/US/products/ps6350/index.html

Overview of QoS

Typically, networks operate on a best-effort delivery basis, which means that all traffic has equal priority and an equal chance of being delivered in a timely manner. When congestion occurs, all traffic has an equal chance of being dropped.

QoS selects network traffic (both unicast and multicast), prioritizes it according to its relative importance, and uses congestion avoidance to provide priority-indexed treatment; QoS can also limit the bandwidth used by network traffic. QoS can make network performance more predictable and bandwidth utilization more effective.

This section contains the following subsections:

•Prioritization

•QoS Terminology

•Basic QoS Model

•Classification

•Policing and Marking

•Mapping Tables

•Queueing and Scheduling

•Packet Modification

Prioritization

The QoS implementation for this release is based on the DiffServ architecture, an emerging standard from the Internet Engineering Task Force (IETF). This architecture specifies that each packet is classified upon entry into the network. The classification is carried in the IP packet header, using 6 bits from the deprecated IP type of service (TOS) field to carry the classification (class) information. Classification can also be carried in the Layer 2 frame. These special bits in the Layer 2 frame or a Layer 3 packet are described here and shown in Figure 27-1:

•Prioritization values in Layer 2 frames:

Layer 2 Inter-Switch Link (ISL) frame headers have a 1-byte User field that carries an IEEE 802.1p class of service (CoS) value in the three least-significant bits. On interfaces configured as Layer 2 ISL trunks, all traffic is in ISL frames.

Layer 2 802.1Q frame headers have a 2-byte Tag Control Information field that carries the CoS value in the three most-significant bits, which are called the User Priority bits. On interfaces configured as Layer 2 802.1Q trunks, all traffic is in 802.1Q frames except for traffic in the native VLAN.

Other frame types cannot carry Layer 2 CoS values.

Layer 2 CoS values range from 0 for low priority to 7 for high priority.

•Prioritization bits in Layer 3 packets:

Layer 3 IP packets can carry either an IP precedence value or a Differentiated Services Code Point (DSCP) value. QoS supports the use of either value because DSCP values are backward-compatible with IP precedence values.

IP precedence values range from 0 to 7.

DSCP values range from 0 to 63.

Figure 27-1 QoS Classification Layers in Frames and Packets

All switches and routers across the Internet rely on the class information to provide the same forwarding treatment to packets with the same class information and different treatment to packets with different class information. The class information in the packet can be assigned by end hosts or by switches or routers along the way, based on a configured policy, detailed examination of the packet, or both. Detailed examination of the packet is expected to happen closer to the edge of the network so that the core switches and routers are not overloaded.

Switches and routers along the path can use the class information to limit the amount of resources allocated per traffic class. The behavior of an individual device when handling traffic in the DiffServ architecture is called per-hop behavior. If all devices along a path provide a consistent per-hop behavior, you can construct an end-to-end QoS solution.

Implementing QoS in your network can be a simple or complex task and depends on the QoS features offered by your internetworking devices, the traffic types and patterns in your network, and the granularity of control you need over incoming and outgoing traffic.

QoS Terminology

The following terms are used when discussing QoS features:

•Packets carry traffic at Layer 3.

•Frames carry traffic at Layer 2. Layer 2 frames carry Layer 3 packets.

•Labels are prioritization values carried in Layer 3 packets and Layer 2 frames:

–Layer 2 class of service (CoS) values, which range between zero for low priority and seven for high priority:

Layer 2 Inter-Switch Link (ISL) frame headers have a 1-byte User field that carries an IEEE 802.1p CoS value in the three least significant bits.

Layer 2 802.1Q frame headers have a 2-byte Tag Control Information field that carries the CoS value in the three most significant bits, which are called the User Priority bits.

Other frame types cannot carry Layer 2 CoS values.

Note On interfaces configured as Layer 2 ISL trunks, all traffic is in ISL frames. On interfaces configured as Layer 2 802.1Q trunks, all traffic is in 802.1Q frames except for traffic in the native VLAN.

–Layer 3 IP precedence values—The IP version 4 specification defines the three most significant bits of the 1-byte ToS field as IP precedence. IP precedence values range between zero for low priority and seven for high priority.

–Layer 3 differentiated services code point (DSCP) values—The Internet Engineering Task Force (IETF) has defined the six most significant bits of the 1-byte IP ToS field as the DSCP. The per-hop behavior represented by a particular DSCP value is configurable. DSCP values range between 0 and 63. See the "Configuring DSCP Maps" section.

Note Layer 3 IP packets can carry either an IP precedence value or a DSCP value. QoS supports the use of either value, since DSCP values are backwards compatible with IP precedence values. See Table 27-1.

•Classification is the selection of traffic to be marked.

•Marking, according to RFC 2475, is the process of setting a Layer 3 DSCP value in a packet; in this publication, the definition of marking is extended to include setting Layer 2 CoS values.

•Scheduling is the assignment of Layer 2 frames to a queue. QoS assigns frames to a queue based on internal DSCP values as shown in Internal DSCP Values.

•Policing is limiting bandwidth used by a flow of traffic. Policing can mark or drop traffic.

Basic QoS Model

Figure 27-2 shows the basic QoS model. Actions at the ingress and egress interfaces include classifying traffic, policing, and marking:

•Classifying distinguishes one kind of traffic from another. The process generates an internal DSCP for a packet, which identifies all the future QoS actions to be performed on this packet. For more information, see the "Classification" section.

•Policing determines whether a packet is in or out of profile by comparing the traffic rate to the configured policer, which limits the bandwidth consumed by a flow of traffic. The result of this determination is passed to the marker. For more information, see the "Policing and Marking" section.

•Marking evaluates the policer configuration information regarding the action to be taken when a packet is out of profile and decides what to do with the packet (pass through a packet without modification, mark down the DSCP value in the packet, or drop the packet). For more information, see the "Policing and Marking" section.

Actions at the egress interface include queueing and scheduling:

•Queueing evaluates the internal DSCP and determines which of the four egress queues in which to place the packet.

•Scheduling services the four egress (transmit) queues based on the sharing and shaping configuration of the egress (transmit) port. Sharing and shaping configurations are described in the "Queueing and Scheduling" section.

Figure 27-2 Basic QoS Model

Classification

Classification is the process of distinguishing one kind of traffic from another by examining the fields in the packet. Classification is enabled only if QoS is globally enabled on the switch. By default, QoS is globally disabled, so no classification occurs.

You specify which fields in the frame or packet that you want to use to classify incoming traffic.

Classification options are shown in Figure 27-3.

For non-IP traffic, you have the following classification options:

•Use the port default. If the packet is a non-IP packet, assign the default port DSCP value to the incoming packet.

•Trust the CoS value in the incoming frame (configure the port to trust CoS). Then use the configurable CoS-to-DSCP map to generate the internal DSCP value. Layer 2 ISL frame headers carry the CoS value in the three least-significant bits of the 1-byte User field. Layer 2 802.1Q frame headers carry the CoS value in the three most-significant bits of the Tag Control Information field. CoS values range from 0 for low priority to 7 for high priority. If the frame does not contain a CoS value, assign the default port CoS to the incoming frame.

The trust DSCP configuration is meaningless for non-IP traffic. If you configure a port with trust DSCP and non-IP traffic is received, the switch assigns the default port DSCP.

For IP traffic, you have the following classification options:

•Trust the IP DSCP in the incoming packet (configure the port to trust DSCP), and assign the same DSCP to the packet for internal use. The IETF defines the six most-significant bits of the 1-byte Type of Service (ToS) field as the DSCP. The priority represented by a particular DSCP value is configurable. DSCP values range from 0 to 63.

•Trust the CoS value (if present) in the incoming packet, and generate the DSCP by using the CoS-to-DSCP map.

•Perform the classification based on a configured IP standard or extended ACL, which examines various fields in the IP header. If no ACL is configured, the packet is assigned the default DSCP based on the trust state of the ingress port; otherwise, the policy map specifies the DSCP to assign to the incoming frame.

For information on the maps described in this section, see the "Mapping Tables" section. For configuration information on port trust states, see the "Configuring the Trust State of Interfaces" section.

Figure 27-3 Classification Flowchart

Classification Based on QoS ACLs

A packet can be classified for QoS using multiple match criteria, and the classification can specify whether the packet should match all of the specified match criteria or at least one of the match criteria. To define a QoS classifier, you can provide the match criteria using the 'match' statements in a class-map. In the 'match' statements, you can specify the fields in the packet to match on, or you can use IP standard or IP extended ACLs. For more information, see the "Classification Based on Class Maps and Policy Maps" section.

If the class-map is configured to match all the match criteria, then a packet must satisfy all the match statements in the class-map before the QoS action is taken. The QoS action for the packet is not taken if the packet does not match even one match criterion in the class-map.

If the class-map is configured to match at least one match criterion, then a packet must satisfy at least one of the match statements in the class-map before the QoS action is taken. The QoS action for the packet is not taken if the packet does not match any match criteria in the class-map.

Note When you use the IP standard and IP extended ACLs, the permit and deny ACEs in the ACL have a slightly different meaning in the QoS context.

•If a packet encounters (and satisfies) an ACE with a "permit," then the packet "matches" the match criterion in the QoS classification.

•If a packet encounters (and satisfies) an ACE with a "deny," then the packet "does not match" the match criterion in the QoS classification.

•If no match with a permit action is encountered and all the ACEs have been examined, then the packet "does not match" the criterion in the QoS classification.

Note When creating an access list, remember that, by default, the end of the access list contains an implicit deny statement for everything if it did not find a match before reaching the end.

After a traffic class has been defined with the class map, you can create a policy that defines the QoS actions for a traffic class. A policy might contain multiple classes with actions specified for each one of them. A policy might include commands to classify the class as a particular aggregate (for example, assign a DSCP) or rate limit the class. This policy is then attached to a particular port on which it becomes effective.

You implement IP ACLs to classify IP traffic by using the access-list global configuration command. For configuration information, see the "Configuring a QoS Policy" section.

Classification Based on Class Maps and Policy Maps

A class map is a mechanism that you use to isolate and name a specific traffic flow (or class) from all other traffic. The class map defines the criterion used to match against a specific traffic flow to further classify it; the criteria can include matching the access group defined by the ACL or matching a specific list of DSCP or IP precedence values. If you have more than one type of traffic that you want to classify, you can create another class map and use a different name. After a packet is matched against the class-map criteria, you can specify the QoS actions via a policy map.

A policy map specifies the QoS actions for the traffic classes. Actions can include trusting the CoS or DSCP values in the traffic class; setting a specific DSCP or IP precedence value in the traffic class; or specifying the traffic bandwidth limitations and the action to take when the traffic is out of profile. Before a policy map can be effective, you must attach it to an interface.

You create a class map by using the class-map global configuration command. When you enter the class-map command, the switch enters the class-map configuration mode. In this mode, you define the match criteria for the traffic by using the match class-map configuration command.

You create and name a policy map by using the policy-map global configuration command. When you enter this command, the switch enters the policy-map configuration mode. In this mode, you specify the actions to take on a specific traffic class by using the trust or set policy-map configuration and policy-map class configuration commands. To make the policy map effective, you attach it to an interface by using the service-policy interface configuration command.

The policy map can also contain commands that define the policer, (the bandwidth limitations of the traffic) and the action to take if the limits are exceeded. For more information, see the "Policing and Marking" section.

A policy map also has these characteristics:

•A policy map can contain up to 255 class statements.

•You can have different classes within a policy-map.

•A policy-map trust state supersedes an interface trust state.

For configuration information, see the "Configuring a QoS Policy" section.

Policing and Marking

After a packet is classified and has an internal DSCP value assigned to it, the policing and marking process can begin as shown in Figure 27-4.

Policing involves creating a policer that specifies the bandwidth limits for the traffic. Packets that exceed the limits are out of profile or nonconforming. Each policer specifies the action to take for packets that are in or out of profile. These actions, carried out by the marker, include passing through the packet without modification, dropping the packet, or marking down the packet with a new DSCP value that is obtained from the configurable policed-DSCP map. For information on the policed-DSCP map, see the "Mapping Tables" section.

You can create these types of policers:

•Individual

QoS applies the bandwidth limits specified in the policer separately to each matched traffic class for each port/VLAN to which the policy-map is attached to. You configure this type of policer within a policy map by using the police command under policy-map class configuration mode.

•Aggregate

QoS applies the bandwidth limits specified in an aggregate policer cumulatively to all matched traffic flows. You configure this type of policer by specifying the aggregate policer name within a policy map by using the police aggregate policy-map configuration command. You specify the bandwidth limits of the policer by using the qos aggregate-policer global configuration command. In this way, the aggregate policer is shared by multiple classes of traffic within a policy map.

When configuring policing and policers, keep these items in mind:

•For IP packets, only the length of the IP payload (the total length field in the IP header) is used by the policer for policing computation. The Layer 2 header and trailer length are not taken into account. For example, for a 64-byte Ethernet II IP packet, only 46 bytes are taken into account for policing (64 bytes - 14 byte Ethernet Header - 4 bytes Ethernet CRC).

For non-IP packets, the Layer 2 length as specified in the Layer 2 Header is used by the policer for policing computation. To specify additional Layer 2 encapsulation length when policing IP packets, use the qos account layer2 encapsulation command.

•By default, no policers are configured.

•Only the average rate and committed burst parameters are configurable.

•Policing can occur on ingress and egress interfaces:

–1020 policers are supported on ingress

–1020 policers are supported on egress

Note Policers 0 through 3 are reserved.

–All policers can be individual or aggregate.

–Two input and two output policers are reserved and used for "no policing" policers.

•On an interface configured for QoS, all traffic received or sent through the interface is classified, policed, and marked according to the policy-map attached to the interface. However, if the interface is configured to use VLAN-based QoS (using the qos vlan-based command), the traffic received or sent through the interface is classified, policed, and marked according to the policy-map attached to the VLAN (configured on the VLAN interface) to which the packet belongs. If there is no policy-map attached to the VLAN to which the packet belongs, the policy-map attached to the interface is used.

After you configure the policy map and policing actions, attach the policy to an ingress or egress interface by using the service-policy interface configuration command. For configuration information, see the "Configuring a QoS Policy" section and the "Creating Named Aggregate Policers" section.

Figure 27-4 Policing and Marking Flowchart

Internal DSCP Values

The following sections describe the internal DSCP values:

•Internal DSCP Sources

•Egress ToS and CoS Sources

Internal DSCP Sources

During processing, QoS represents the priority of all traffic (including non-IP traffic) with an internal DSCP value. QoS derives the internal DSCP value from the following:

•For trust-CoS traffic, from received or ingress interface Layer 2 CoS values

•For trust-DSCP traffic, from received or ingress interface DSCP values

•For untrusted traffic, from ingress interface DSCP value

The trust state of traffic is the trust state of the ingress interface unless set otherwise by a policy action for this traffic class.

QoS uses configurable mapping tables to derive the internal 6-bit DSCP value from CoS, which are 3-bit values (see the"Configuring DSCP Maps" section).

Egress ToS and CoS Sources

For egress IP traffic, QoS creates a ToS byte from the internal DSCP value and sends it to the egress interface to be written into IP packets. For trust-dscp and untrusted IP traffic, the ToS byte includes the original 2 least-significant bits from the received ToS byte.

Note The internal ToS value can mimic an IP precedence value (see Table 27-1).

For all egress traffic, QoS uses a configurable mapping table to derive a CoS value from the internal ToS value associated with traffic (see the "Configuring the DSCP-to-CoS Map" section). QoS sends the CoS value to be written into ISL and 802.1Q frames.

For traffic received on an ingress interface configured to trust CoS using the qos trust cos command, the transmit CoS is always the incoming packet CoS (or the ingress interface default CoS if the packet is received untagged).

When the interface trust state is not configured to trust dscp using the qos trust dscp command, the security and QoS ACL classification will always use the interface DSCP and not the incoming packet DSCP.

Mapping Tables

During QoS processing, the switch represents the priority of all traffic (including non-IP traffic) with an internal DSCP value:

•During classification, QoS uses configurable mapping tables to derive the internal DSCP (a 6-bit value) from received CoS. These maps include the CoS-to-DSCP map.

•During policing, QoS can assign another DSCP value to an IP or non-IP packet (if the packet is out of profile and the policer specifies a marked down DSCP value). This configurable map is called the policed-DSCP map.

•Before the traffic reaches the scheduling stage, QoS uses the internal DSCP to select one of the four egress queues for output processing. The DSCP-to-egress queue mapping can be configured using the qos map dscp to tx-queue command.

The CoS-to-DSCP and DSCP-to-CoS map have default values that might or might not be appropriate for your network.

For configuration information, see the "Configuring DSCP Maps" section.

Queueing and Scheduling

Each physical port has four transmit queues (egress queues). Each packet that needs to be transmitted is enqueued to one of the transmit queues. The transmit queues are then serviced based on the transmit queue scheduling algorithm.

Once the final transmit DSCP is computed (including any markdown of DSCP), the transmit DSCP to transmit queue mapping configuration determines the transmit queue. The packet is placed in the transmit queue of the transmit port, determined from the transmit DSCP. Use the qos map dscp to tx-queue command to configure the transmit DSCP to transmit queue mapping. The transmit DSCP is the internal DSCP value if the packet is a non-IP packet as determined by the QoS policies and trust configuration on the ingress and egress ports.

For configuration information, see the "Configuring Transmit Queues" section.

Active Queue Management

Active queue management (AQM) is the pro-active approach of informing you about congestion before a buffer overflow occurs. AQM is done using Dynamic buffer limiting (DBL). DBL tracks the queue length for each traffic flow in the switch. When the queue length of a flow exceeds its limit, DBL will drop packets or set the Explicit Congestion Notification (ECN) bits in the packet headers.

DBL classifies flows in two categories, adaptive and aggressive. Adaptive flows reduce the rate of packet transmission once it receives congestion notification. Aggressive flows do not take any corrective action in response to congestion notification. For every active flow the switch maintains two parameters, "buffersUsed" and "credits". All flows start with "max-credits", a global parameter. When a flow with credits less than "aggressive-credits" (another global parameter) it is considered an aggressive flow and is given a small buffer limit called "aggressiveBufferLimit".

Queue length is measured by the number of packets. The number of packets in the queue determines the amount of buffer space that a flow is given. When a flow has a high queue length the computed value is lowered. This allows new incoming flows to receive buffer space in the queue. This allows all flows to get a proportional share of packets through the queue.

Sharing Link Bandwidth Among Transmit Queues

The four transmit queues for a transmit port share the available link bandwidth of that transmit port. You can set the link bandwidth to be shared differently among the transmit queues using bandwidth command in interface transmit queue configuration mode. With this command, you assign the minimum guaranteed bandwidth for each transmit queue.

By default, all queues are scheduled in a round robin manner.

For systems using Supervisor Engine II-Plus, Supervisor Engine II-Plus TS, Supervisor Engine III, and Supervisor Engine IV, bandwidth can be configured on these ports only:

•Uplink ports on supervisor engines

•Ports on the WS-X4306-GB module

•The 2 1000BASE-X ports on the WS-X4232-GB-RJ module

•The first 2 ports on the WS-X4418-GB module

•The two 1000BASE-X ports on the WS-X4412-2GB-TX module

For systems using Supervisor Engine V, bandwidth can be configured on all ports (10/100 Fast Ethernet, 10/100/1000BASE-T, and 1000BASE-X).

Strict Priority / Low Latency Queueing

You can configure transmit queue 3 on each port with higher priority using the priority high tx-queue configuration command in the interface configuration mode. When transmit queue 3 is configured with higher priority, packets in transmit queue 3 are scheduled ahead of packets in other queues.

When transmit queue 3 is configured at a higher priority, the packets are scheduled for transmission before the other transmit queues only if it has not met the allocated bandwidth sharing configuration. Any traffic that exceeds the configured shape rate will be queued and transmitted at the configured rate. If the burst of traffic, exceeds the size of the queue, packets will be dropped to maintain transmission at the configured shape rate.

Traffic Shaping

Traffic Shaping provides the ability to control the rate of outgoing traffic in order to make sure that the traffic conforms to the maximum rate of transmission contracted for it. Traffic that meets certain profile can be shaped to meet the downstream traffic rate requirements to handle any data rate mismatches.

Each transmit queue can be configured to transmit a maximum rate using the shape command. The configuration allows you to specify the maximum rate of traffic. Any traffic that exceeds the configured shape rate will be queued and transmitted at the configured rate. If the burst of traffic exceeds the size of the queue, packets will be dropped to maintain transmission at the configured shape rate.

Packet Modification

A packet is classified, policed, and queued to provide QoS. Packet modifications can occur during this process:

•For IP packets, classification involves assigning a DSCP to the packet. However, the packet is not modified at this stage; only an indication of the assigned DSCP is carried along. The reason for this is that QoS classification and ACL lookup occur in parallel, and it is possible that the ACL specifies that the packet should be denied and logged. In this situation, the packet is forwarded with its original DSCP to the CPU, where it is again processed through ACL software.

•For non-IP packets, classification involves assigning an internal DSCP to the packet, but because there is no DSCP in the non-IP packet, no overwrite occurs. Instead, the internal DSCP is used both for queueing and scheduling decisions and for writing the CoS priority value in the tag if the packet is being transmitted on either an ISL or 802.1Q trunk port.

•During policing, IP and non-IP packets can have another DSCP assigned to them (if they are out of profile and the policer specifies a markdown DSCP). Once again, the DSCP in the packet is not modified, but an indication of the marked-down value is carried along. For IP packets, the packet modification occurs at a later stage.

QoS and Software Processed Packets

The Catalyst 4500 platform does not apply the QoS marking or policing configuration for any packets that are forwarded or generated by the Cisco IOS software. This means that any input or output QoS policy configured on the port or VLAN is not applied to packets if the Cisco IOS is forwarding or generating packets.

However, Cisco IOS marks all the generated control packets appropriately and uses the internal IP DSCP to determine the transmit queue on the output transmission interface. For IP packets, the internal IP DSCP is the IP DSCP field in the IP packet. For non-IP packets, Cisco IOS assigns a packet priority internally and maps it to an internal IP DSCP value.

Cisco IOS assigns an IP precedence of 6 to routing protocol packets on the control plane. As noted in RFC 791,"The Internetwork Control designation is intended for use by gateway control originators only." Specifically, Cisco IOS marks the following IP-based control packets: Open Shortest Path First (OSPF), Routing Information Protocol (RIP), Enhanced Interior Gateway Routing Protocol (EIGRP) hellos, and keepalives. Telnet packets to and from the router also receive an IP precedence value of 6. The assigned value remains with the packets when the output interface transmits them into the network.

For Layer 2 control protocols, the software assigns an internal IP DSCP. Typically, Layer 2 control protocol packets are assigned an internal DSCP value of 48 (corresponding to an IP precedence value of 6).

The internal IP DSCP is used to determine the transmit queue to which the packet is enqueued on the transmission interface. See "Configuring Transmit Queues" on page 40 for details on how to configure the DSCP to transmit queues.

The internal IP DSCP is also used to determine the transmit CoS marking if the packet is transmitted with a IEEE 802.1q or ISL tag on a trunk interface. See "Configuring the DSCP-to-CoS Map" on page 44 for details on how to configure the DSCP to CoS mapping.

Configuring Auto-QoS

You can use the auto-QoS feature to simplify the deployment of existing QoS features. Auto-QoS makes assumptions about the network design, and as a result, the switch can prioritize different traffic flows and appropriately use the egress queues instead of using the default QoS behavior. (The default is that QoS is disabled. The switch then offers best-effort service to each packet, regardless of the packet content or size, and sends it from a single queue.)

When you enable auto-QoS, it automatically classifies traffic based on ingress packet label. The switch uses the resulting classification to choose the appropriate egress queue.

You use auto-QoS commands to identify ports connected to Cisco IP phones and to identify ports that receive trusted voice over IP (VoIP) traffic through an uplink. Auto-QoS then performs these functions:

•Detects the presence or absence of IP phones

•Configures QoS classification

•Configures egress queues

These sections describe how to configure auto-QoS on your switch:

•Generated Auto-QoS Configuration

•Effects of Auto-QoS on the Configuration

•Configuration Guidelines

•Enabling Auto-QoS for VoIP

Generated Auto-QoS Configuration

By default, auto-QoS is disabled on all interfaces.

When you enable the auto-QoS feature on the first interface, these automatic actions occur:

•QoS is globally enabled (qos global configuration command).

•DBL is enabled globally (qos dbl global configuration command)

•When you enter the auto qos voip trust interface configuration command, the ingress classification on the specified interface is set to trust the CoS label received in the packet if the specified interface is configured as Layer 2 (and is set to trust DSCP if the interface is configured as Layer 3). (See Table 27-2.)

•When you enter the auto qos voip cisco-phone interface configuration command, the trusted boundary feature is enabled. It uses the Cisco Discovery Protocol (CDP) to detect the presence or absence of a Cisco IP phone. When a Cisco IP phone is detected, the ingress classification on the interface is set to trust the cos label received in the packet, because some old phones do not mark dscp. When a Cisco IP phone is absent, the ingress classification is set to not trust the cos label in the packet.

For information about the trusted boundary feature, see the "Configuring a Trusted Boundary to Ensure Port Security" section.

When you enable auto-QoS by using the auto qos voip cisco-phone or the auto qos voip trust interface configuration commands, the switch automatically generates a QoS configuration based on the traffic type and ingress packet label and applies the commands listed in Table 27-2 to the interface.

Switch(config)# qos

Switch(config)# qos map cos 3 to 26

Switch(config)# qos dbl

Switch(config)# qos map cos 5 to 46

Switch(config)# qos map dscp 24 25 26 27 b28 29 30 
31 to tx-queue 4

Switch(config)# qos map dscp 32 33 34 35 36 37 38 39 
to tx-queue 4

Switch(config-if)# qos trust cos

or

Switch(config-if)# qos trust dscp

Switch(config)# policy-map autoqos-voip-policy

Switch(config-pmap)# class class-default

Switch(config-pmap-c)# dbl

Switch(config-if)# qos trust device cisco-phone

Switch(config-if)# tx-queue 3

Switch(config-if-tx-queue)# priority high

Switch(config-if-tx-queue)# shape percent 33

Switch(config-if-tx-queue)# bandwidth percent 33

Effects of Auto-QoS on the Configuration

When auto-QoS is enabled, the auto qos voip interface configuration command and the generated configuration are added to the running configuration.

Configuration Guidelines

Before configuring auto-QoS, you should be aware of this information:

•In this release, auto-QoS configures the switch only for VoIP with Cisco IP phones.

•To take advantage of the auto-QoS defaults, do not configure any standard-QoS commands before entering the auto-QoS commands. If necessary, you can fine-tune the QoS configuration, but we recommend that you do so only after the auto-QoS configuration is completed.

•You can enable auto-QoS on static, dynamic-access, voice VLAN access, and trunk ports.

•By default, the CDP is enabled on all interfaces. For auto-QoS to function properly, do not disable the CDP.

•To enable auto qos voip trust on Layer 3 interfaces, change the port to Layer 3, then apply auto-QoS to make it trust DSCP.

Enabling Auto-QoS for VoIP

To enable auto-QoS for VoIP within a QoS domain, perform this task:

Switch# configure terminal

To disable auto-QoS on an interface, use the no auto qos voip interface configuration command. When you enter this command, the switch changes the auto-QoS settings to the standard-QoS default settings for that interface. It will not change any global configuration performed by auto-QoS. Global configuration remains the same.

This example shows how to enable auto-QoS and to trust the CoS labels in incoming packets when the device connected to Fast Ethernet interface 1/1 is detected as a Cisco IP phone:

Switch(config)# interface fastethernet1/1

Switch(config-if)# auto qos voip cisco-phone

This example shows how to enable auto-QoS and to trust the cos/dscp labels in incoming packets when the switch or router connected to Gigabit Ethernet interface 1/1 is a trusted device:

Switch(config)# interface gigabitethernet1/1

Switch(config-if)# auto qos voip trust

This example shows how to display the QoS commands that are automatically generated when auto-QoS is enabled:

Switch# debug auto qos

AutoQoS debugging is on

Switch# configure terminal

Enter configuration commands, one per line.  End with CNTL/Z. 

Switch(config)# interface gigabitethernet1/1

Switch(config-if)# auto qos voip cisco-phone

Displaying Auto-QoS Information

To display the initial auto-QoS configuration, use the show auto qos [interface [interface-id]] privileged EXEC command. To display any user changes to that configuration, use the show running-config privileged EXEC command. You can compare the show auto qos and the show running-config command output to identify the user-defined QoS settings.

To display information about the QoS configuration that might be affected by auto-QoS, use one of these commands:

•show qos

•show qos map

•show qos interface [interface-id]

For more information about these commands, refer to the command reference for this release.

Auto-QoS Configuration Example

This section describes how you could implement auto-QoS in a network, as shown in Figure 27-5.

Figure 27-5 Auto-QoS Configuration Example Network

The intelligent wiring closets in Figure 27-5 are composed of Catalyst 4500 switches. The object of this example is to prioritize the VoIP traffic over all other traffic. To do so, enable auto-QoS on the switches at the edge of the QoS domains in the wiring closets.

Note You should not configure any standard QoS commands before entering the auto-QoS commands. You can fine-tune the QoS configuration, but we recommend that you do so only after the auto-QoS configuration is completed.

To configure the switch at the edge of the QoS domain to prioritize the VoIP traffic over all other traffic, perform this task:

Configuring QoS

Before configuring QoS, you must have a thorough understanding of these items:

•The types of applications used and the traffic patterns on your network.

•Traffic characteristics and needs of your network. Is the traffic bursty? Do you need to reserve bandwidth for voice and video streams?

•Bandwidth requirements and speed of the network.

•Location of congestion points in the network.

These sections describe how to configure QoS on the Catalyst 4000 family switch:

•Default QoS Configuration

•Configuration Guidelines

•Enabling QoS Globally

•Configuring a Trusted Boundary to Ensure Port Security

•Enabling Dynamic Buffer Limiting

•Creating Named Aggregate Policers

•Configuring a QoS Policy

•Enabling or Disabling QoS on an Interface

•Configuring VLAN-Based QoS on Layer 2 Interfaces

•Configuring the Trust State of Interfaces

•Configuring the CoS Value for an Interface

•Configuring DSCP Values for an Interface

•Configuring Transmit Queues

•Configuring DSCP Maps

Default QoS Configuration

Table 27-3 shows the QoS default configuration.

Configuration Guidelines

Before beginning the QoS configuration, you should be aware of this information:

•If you have EtherChannel ports configured on your switch, you must configure QoS classification and policing on the EtherChannel. The transmit queue configuration must be configured on the individual physical ports that comprise the EtherChannel.

•It is not possible to match IP fragments against configured IP extended ACLs to enforce QoS. IP fragments are transmitted as best effort. IP fragments are denoted by fields in the IP header.

•It is not possible to match IP options against configured IP extended ACLs to enforce QoS. These packets are sent to the CPU and processed by software. IP options are denoted by fields in the IP header.

•Control traffic (such as spanning-tree BPDUs and routing update packets) received by the switch are subject to all ingress QoS processing.

•If you want to use the set command in the policy map, you must enable IP routing (disabled by default) and configure an IP default route to send traffic to the next-hop device that is capable of forwarding.

Note QoS processes both unicast and multicast traffic.

Enabling QoS Globally

To enable QoS globally, perform this task:

Switch(config)# qos 

Switch(config)# end 

Switch# show qos 

This example shows how to enable QoS globally:

Switch(config)# qos 

Switch(config)# end 

Switch#

This example shows how to verify the configuration:

Switch# show qos 

  QoS is enabled globally

Switch#

Configuring a Trusted Boundary to Ensure Port Security

In a typical network, you connect a Cisco IP phone to a switch port as discussed in Chapter 28, "Configuring Voice Interfaces." Traffic sent from the telephone to the switch is typically marked with a tag that uses the 802.1Q header. The header contains the VLAN information and the class of service (CoS) 3-bit field, which determines the priority of the packet. For most Cisco IP phone configurations, the traffic sent from the telephone to the switch is trusted to ensure that voice traffic is properly prioritized over other types of traffic in the network. By using the qos trust cos interface configuration command, you can configure the switch port to which the telephone is connected to trust the CoS labels of all traffic received on that port.

In some situations, you also might connect a PC or workstation to the IP phone. In this case, you can use the switchport priority extend cos interface configuration command to configure the telephone through the switch CLI to override the priority of the traffic received from the PC. With this command, you can prevent a PC from taking advantage of a high-priority data queue.

However, if a user bypasses the telephone and connects the PC directly to the switch, the CoS labels generated by the PC are trusted by the switch (because of the trusted CoS setting) and can allow misuse of high-priority queues. The trusted boundary feature solves this problem by using the CDP to detect the presence of a Cisco IP phone (such as the Cisco IP Phone 7910, 7935, 7940, and 7960) on a switch port.

Note If CDP is not running on the switch globally or on the port in question, trusted boundary will not work.

When you configure trusted boundary on a port, trust is disabled. Then, when a phone is plugged in and detected, trust is enabled. (It may take a few minutes to detect the phone.) Now, when a phone is unplugged (and not detected), the trusted boundary feature disables the trusted setting on the switch port and prevents misuse of a high-priority queue.

To enable trusted boundary on a port, perform this task:

Switch# configure terminal

To disable the trusted boundary feature, use the no qos trust device cisco-phone interface configuration command.

Enabling Dynamic Buffer Limiting

To enable DBL globally on the switch, perform this task:

Switch(config)# qos dbl

Switch(config)# end 

Switch# show qos dbl

This example shows how to enable DBL globally:

Switch(config)# qos dbl

Global DBL enabled

Switch(config)# end 

Switch#

This example shows how to verify the configuration:

Switch# show qos dbl

DBL is enabled globally

DBL flow includes vlan

DBL flow includes l4-ports

DBL does not use ecn to indicate congestion

DBL exceed-action mark probability:15%

DBL max credits:15

DBL aggressive credit limit:10

DBL aggressive buffer limit:2 packets

Switch#

Creating Named Aggregate Policers

To create a named aggregate policer, perform this task:

An aggregate policer can be applied to one or more interfaces. However, if you apply the same policer to the input direction on one interface and to the output direction on a different interface, then you have created the equivalent of two different aggregate policers in the switching engine. Each policer has the same policing parameters, with one policing the ingress traffic on one interface and the other policing the egress traffic on another interface. If an aggregate policer is applied to multiple interfaces in the same direction, then only one instance of the policer is created in the switching engine.

Similarly, an aggregate policer can be applied to a port or to a VLAN. If you apply the same aggregate policer to a port and to a VLAN, then you have created the equivalent of two different aggregate policers in the switching engine. Each policer has the same policing parameters, with one policing the traffic on the configured port and the other policing the traffic on the configured VLAN. If an aggregate policer is applied to only ports or only VLANs, then only one instance of the policer is created in the switching engine.

In effect, if you apply a single aggregate policer to ports and VLANs in different directions, then you have created the equivalent of four aggregate policers; one for all ports sharing the policer in input direction, one for all ports sharing the policer in output direction, one for all VLANs sharing the policer in input direction and one for all VLANs sharing the policer in output direction.

When creating a named aggregate policer, note the following:

•The valid range of values for the rate parameter is as follows:

–Minimum—32 kilobits per second

–Maximum—32 gigabits per second

See the "Configuration Guidelines" section.

•Rates can be entered in bits-per-second, or you can use the following abbreviations:

–k to denote 1000 bps

–m to denote 1000000 bps

–g to denote 1000000000 bps

Note You can also use a decimal point. For example, a rate of 1,100,000 bps can be entered
as 1.1m.

•The valid range of values for the burst parameter is as follows:

–Minimum—1 kilobyte

–Maximum—512 megabytes

•Bursts can be entered in bytes, or you can use the following abbreviation:

–k to denote 1000 bytes

–m to denote 1000000 bytes

–g to denote 1000000000 bytes

Note You can also use a decimal point. For example, a burst of 1,100,000 bytes can be entered
as 1.1m.

•Optionally, you can specify a conform action for matched in-profile traffic as follows:

–The default conform action is transmit.

–Enter the drop keyword to drop all matched traffic.

Note When you configure drop as the conform action, QoS configures drop as the exceed action.

•Optionally, for traffic that exceeds the CIR, you can specify an exceed action as follows:

–The default exceed action is drop.

–Enter the policed-dscp-transmit keyword to cause all matched out-of-profile traffic to be marked down as specified in the markdown map.

–For no policing, enter the transmit keyword to transmit all matched out-of-profile traffic.

•You can enter the no qos aggregate-policer policer_name command to delete a named aggregate policer.

This example shows how to create a named aggregate policer with a 10 Mbps rate limit and a 1-MB burst size that transmits conforming traffic and marks down out-of-profile traffic.

Switch(config)# qos aggregate-policer aggr-1 10000000 1000000 conform-action transmit 
exceed-action policed-dscp-transmit

Switch(config)# end

Switch#

This example shows how to verify the configuration:

Switch# show qos aggregate-policer aggr-1

Policer aggr-1

  Rate(bps):10000000 Normal-Burst(bytes):1000000

  conform-action:transmit exceed-action:policed-dscp-transmit  

  Policymaps using this policer:

Switch#

Configuring a QoS Policy

The following subsections describe QoS policy configuration:

•Overview of QoS Policy Configuration

•Configuring a Class Map (Optional)

•Verifying Class-Map Configuration

•Configuring a Policy Map

•Verifying Policy-Map Configuration

•Attaching a Policy Map to an Interface

Note QoS policies process both unicast and multicast traffic.

Overview of QoS Policy Configuration

Configuring a QoS policy requires you to configure traffic classes and the policies that will be applied to those traffic classes, and to attach the policies to interfaces using these commands:

•access-list (optional for IP traffic—you can filter IP traffic with class-map commands):

–QoS supports these access list types:

–See Chapter 33, "Configuring Network Security with ACLs," for information about ACLs on the Catalyst 4500 series switches.

•class-map (optional)—Enter the class-map command to define one or more traffic classes by specifying the criteria by which traffic is classified. (See the "Configuring a Class Map (Optional)" section.)

•policy-map—Enter the policy-map command to define the following for each class of traffic:

–Internal DSCP source

–Aggregate or individual policing and marking

•service-policy—Enter the service-policy command to attach a policy map to an interface.

Configuring a Class Map (Optional)

The following subsections describe class map configuration:

•Creating a Class Map

•Configuring Filtering in a Class Map

Enter the class-map configuration command to define a traffic class and the match criteria that will be used to identify traffic as belonging to that class. Match statements can include criteria such as an ACL, an IP precedence value, or a DSCP value. The match criteria are defined with one match statement entered within the class-map configuration mode.

Creating a Class Map

To create a class map, perform this task:

Switch(config)# [no] class-map [match-all | 
match-any] class_name 

Configuring Filtering in a Class Map

To configure filtering in a class map, perform one of these tasks:

Switch(config-cmap)# [no] match access-group 
{acl_index | name acl_name} 

Switch (config-cmap)# [no] match ip precedence 
ipp_value1 [ipp_value2 [ipp_valueN]] 

Switch (config-cmap)# [no] match ip dscp dscp_value1 
[dscp_value2 [dscp_valueN]] 

Switch (config-cmap)# [no] match any

Note Any Input or Output policy that uses a class-map with the match ip precedence or match ip dscp class-map commands, requires that the port on which the packet is received, be configured to trust dscp. If the incoming port trust state is not set to trust dscp, the IP packet DSCP/IP-precedence is not used for matching the traffic; instead the receiving port's default DSCP is used.

Note The interfaces on the Catalyst 4000 family switch do not support the match classmap, match destination-address, match input-interface, match mpls, match not, match protocol, match qos-group, and match source-address keywords.

Verifying Class-Map Configuration

To verify class-map configuration, perform this task:

Switch (config-cmap)# end 

Switch# show class-map class_name 

This example shows how to create a class map named ipp5 and how to configure filtering to match traffic with IP precedence 5:

Switch# configure terminal 

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)# class-map ipp5 

Switch(config-cmap)# match ip precedence 5 

Switch(config-cmap)# end 

Switch#

This example shows how to verify the configuration:

Switch# show class-map ipp5 

 Class Map match-all ipp5 (id 1)

   Match ip precedence 5

Switch#

Configuring a Policy Map

You can attach only one policy map to an interface. Policy maps can contain one or more policy-map classes, each with different match criteria and policers.

Configure a separate policy-map class in the policy map for each type of traffic that an interface receives. Put all commands for each type of traffic in the same policy-map class. QoS does not attempt to apply commands from more than one policy-map class to matched traffic.

The following sections describe policy-map configuration:

•Creating a Policy Map

•Configuring Policy-Map Class Actions

Creating a Policy Map

To create a policy map, perform this task:

Switch(config)# [no] policy-map policy_name 

Configuring Policy-Map Class Actions

These sections describe policy-map class action configuration:

•Configuring the Policy-Map Class Trust State

•Configuring the Policy Map Class DBL State

•Configuring Policy-Map Class Policing

•Using a Named Aggregate Policer

•Configuring a Per-Interface Policer

Configuring the Policy-Map Class Trust State

To configure the policy-map class trust state, perform this task:

Switch(config-pmap-c)# [no] trust 
{cos | dscp} 

When configuring the policy-map class trust state, note the following:

•You can enter the no trust command to use the trust state configured on the ingress interface (this is the default).

•With the cos keyword, QoS sets the internal DSCP value from received or interface CoS.

•With the dscp keyword, QoS uses received DSCP.

Configuring the Policy Map Class DBL State

To configure the policy map class DBL state, perform this task:

Switch(config-pmap-c)# [no] dbl

When configuring the policy-map class DBL state, note the following:

•Any class that uses a named aggregate policer must have the same DBL configuration to work.

Configuring Policy-Map Class Policing

These sections describe configuration of policy-map class policing:

•Using a Named Aggregate Policer

•Configuring a Per-Interface Policer

Using a Named Aggregate Policer

To use a named aggregate policer (see the "Creating Named Aggregate Policers" section), perform this task:

Switch(config-pmap-c)# [no] police aggregate 
aggregate_name 

Configuring a Per-Interface Policer

To configure a per-interface policer (see the "Policing and Marking" section), perform this task:

When configuring a per-interface policer, note the following:

•The valid range of values for the rate parameter is as follows:

–Minimum—32 kilobits per second, entered as 32000

–Maximum—32 gigabits per second, entered as 32000000000

Note See the "Configuration Guidelines" section.

•Rates can be entered in bits-per-second, or you can use the following abbreviations:

–k to denote 1000 bps

–m to denote 1000000 bps

–g to denote 1000000000 bps

Note You can also use a decimal point. For example, a rate of 1,100,000 bps can be entered
as 1.1m.

•The valid range of values for the burst parameter is as follows:

–Minimum—1 kilobyte

–Maximum—512 megabytes

•Bursts can be entered in bytes, or you can use the following abbreviation:

–k to denote 1000 bytes

–m to denote 1000000 bytes

–g to denote 1000000000 bytes

Note You can also use a decimal point. For example, a burst of 1,100,000 bytes can be entered
as 1.1m.

•Optionally, you can specify a conform action for matched in-profile traffic as follows:

–The default conform action is transmit.

–You can enter the drop keyword to drop all matched traffic.

•Optionally, for traffic that exceeds the CIR, you can enter the policed-dscp-transmit keyword to cause all matched out-of-profile traffic to be marked down as specified in the markdown map. See "Configuring the Policed-DSCP Map" section.

–For no policing, you can enter the transmit keyword to transmit all matched out-of-profile traffic.

This example shows how to create a policy map named ipp5-policy that uses the class-map named ipp5, is configured to rewrite the packet precedence to 6 and to aggregate police the traffic that matches IP precedence value of 5:

Switch# configure terminal 

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)# policy-map ipp5-policy 

Switch(config-pmap)# class ipp5 

Switch(config-pmap-c)# set ip precedence 6

Switch(config-pmap-c)# dbl

Switch(config-pmap-c)# police 2000000000 2000000 conform-action transmit exceed-action 
policed-dscp-transmit 

Switch(config-pmap-c)# end 

Verifying Policy-Map Configuration

To verify policy-map configuration, perform this task:

Switch(config-pmap-c)# end 

Switch# show policy-map policy_name 

This example shows how to verify the configuration:

Switch# show policy-map ipp5-policy 

show policy ipp5-policy

 Policy Map ipp5-policy

  class  ipp5

   set ip precedence 6

   dbl

police 2000000000 2000000 conform-action transmit exceed-action

policed-dscp-transmit 

Switch#

Attaching a Policy Map to an Interface

To attach a policy map to an interface, perform this task:

Switch(config)# interface {vlan vlan_ID | 
{fastethernet | gigabitethernet} slot/interface | 
Port-channel number} 

Switch(config-if)# [no] service-policy input 
policy_map_name 

Switch(config-if)# end 

Switch# show policy-map interface {vlan vlan_ID | 
{fastethernet | gigabitethernet} slot/interface} 

This example shows how to attach the policy map named pmap1 to Fast Ethernet interface 5/36:

Switch# configure terminal 

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)# interface fastethernet 5/36 

Switch(config-if)# service-policy input pmap1

Switch(config-if)# end

This example shows how to verify the configuration:

Switch# show policy-map interface fastethernet 5/36 

FastEthernet6/1

   service-policy input:p1

     class-map:c1 (match-any)

       238474 packets

       match:access-group 100

        38437 packets

       police:aggr-1

        Conform:383934 bytes Exceed:949888 bytes

    class-map:class-default (match-any)

      0 packets

      match:any 

        0 packets

Switch#

Enabling or Disabling QoS on an Interface

The qos interface command reenables any previously configured QoS features. The qos interface command does not affect the interface queueing configuration.

To enable or disable QoS features for traffic from an interface, perform this task:

Switch(config)# interface {vlan vlan_ID | 
{fastethernet | gigabitethernet} slot/interface | 
Port-channel number} 

Switch(config-if)# [no] qos 

Switch(config-if)# end 

Switch# show qos interface

This example shows how to disable QoS on interface VLAN 5:

Switch# configure terminal 

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)# interface vlan 5 

Switch(config-if)# no qos 

Switch(config-if)# end 

Switch# 

This example shows how to verify the configuration:

Switch# show qos | begin QoS is disabled 

  QoS is disabled on the following interfaces:

    Vl5 

<...Output Truncated...>

Switch#

Configuring VLAN-Based QoS on Layer 2 Interfaces

By default, QoS uses policy maps attached to physical interfaces. For Layer 2 interfaces, you can configure QoS to use policy maps attached to a VLAN. (See the "Attaching a Policy Map to an Interface" section.)

To configure VLAN-based QoS on a Layer 2 interface, perform this task:

Switch(config)# interface {fastethernet | 
gigabitethernet} slot/interface | Port-channel 
number 

Switch(config-if)# [no] qos vlan-based 

Switch(config-if)# end 

Switch# show qos 

Note If no input QoS policy is attached to a Layer 2 interface, then the input QoS policy attached to the VLAN (on which the packet is received), if any, is used even if the port is not configured as VLAN-based. If you do not want this default, attach a placeholder input QoS policy to the Layer 2 interface. Similarly, if no output QoS policy is attached to a Layer 2 interface, then the output QoS policy attached to the VLAN (on which the packet is transmitted), if any, is used even if the port is not configured as VLAN-based. If you do not want this default, attach a placeholder output QoS policy to the layer 2 interface.

This example shows how to configure VLAN-based QoS on Fast Ethernet interface 5/42:

Switch# configure terminal 

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)# interface fastethernet 5/42 

Switch(config-if)# qos vlan-based 

Switch(config-if)# end 

This example shows how to verify the configuration:

Switch# show qos | begin QoS is vlan-based 

QoS is vlan-based on the following interfaces:

    Fa5/42

Switch# 

Note When a layer 2 interface is configured with VLAN-based QoS, and if a packet is received on the port for a VLAN on which there is no QoS policy, then the QoS policy attached to the port, if any is used. This applies for both Input and Output QoS policies.

Configuring the Trust State of Interfaces

This command configures the trust state of interfaces. By default, all interfaces are untrusted.

To configure the trust state of an interface, perform this task;

Switch(config)# interface {vlan vlan_ID | 
{fastethernet | gigabitethernet} slot/interface | 
Port-channel number} 

Switch(config-if)# [no] qos trust [dscp | cos] 

Switch(config-if)# end 

Switch# show qos 

When configuring the trust state of an interface, note the following:

•You can use the no qos trust command to set the interface state to untrusted.

•For traffic received on an ingress interface configured to trust CoS using the qos trust cos command, the transmit CoS is always the incoming packet CoS (or the ingress interface default CoS if the packet is received untagged).

•When the interface trust state is not configured to trust dscp using the qos trust dscp command, the security and QoS ACL classification will always use the interface DSCP and not the incoming packet DSCP.

This example shows how to configure Gigabit Ethernet interface 1/1 with the trust cos keywords:

Switch# configure terminal 

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)# interface gigabitethernet 1/1 

Switch(config-if)# qos trust cos 

Switch(config-if)# end 

Switch# 

This example shows how to verify the configuration:

Switch# show qos interface gigabitethernet 1/1 | include trust 

  Trust state: trust COS

Switch# 

Configuring the CoS Value for an Interface

QoS assigns the CoS value specified with this command to untagged frames from ingress interfaces configured as trusted and to all frames from ingress interfaces configured as untrusted.

To configure the CoS value for an ingress interface, perform this task:

Switch(config)# interface {fastethernet | 
gigabitethernet} slot/interface | Port-channel 
number} 

Switch(config-if)# [no] qos cos default_cos 

Switch(config-if)# end 

Switch# show qos interface {fastethernet | 
gigabitethernet} slot/interface 

This example shows how to configure the CoS 5 as the default on Fast Ethernet interface 5/24:

Switch# configure terminal 

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)# interface fastethernet 5/24 

Switch(config-if)# qos cos 5 

Switch(config-if)# end 

Switch# 

This example shows how to verify the configuration:

Switch# show qos interface fastethernet 5/24 | include Default COS

  Default COS is 5

Switch# 

Configuring DSCP Values for an Interface

QoS assigns the DSCP value specified with this command to non IPv4 frames received on interfaces configured to trust DSCP and to all frames received on interfaces configured as untrusted.

To configure the DSCP value for an ingress interface, perform this task:

Switch(config)# interface {fastethernet | 
gigabitethernet} slot/interface | Port-channel 
number 

Switch(config-if)# [no] qos dscp default_dscp 

Switch(config-if)# end 

Switch# show qos interface {fastethernet | 
gigabitethernet} slot/interface 

This example shows how to configure the DSCP 5 as the default on Fast Ethernet interface 5/24:

Switch# configure terminal 

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)# interface fastethernet 5/24 

Switch(config-if)# qos dscp 5 

Switch(config-if)# end 

Switch# 

This example shows how to verify the configuration:

Switch# show qos interface fastethernet 6/1

QoS is enabled globally

Port QoS is enabled

  Port Trust State:CoS

  Default DSCP:0 Default CoS:0

  Tx-Queue   Bandwidth   ShapeRate   Priority   QueueSize

               (bps)       (bps)                (packets)

    1        31250000    disabled    N/A        240      

    2        31250000    disabled    N/A        240      

    3        31250000    disabled    normal     240      

    4        31250000    disabled    N/A        240

Switch# 

Configuring Transmit Queues

The following sections describes how to configure the transmit queues:

•Mapping DSCP Values to Specific Transmit Queues

•Allocating Bandwidth Among Transmit Queues

•Configuring Traffic Shaping of Transmit Queues

•Configuring a High Priority Transmit Queue

Depending on the complexity of your network and your QoS solution, you might need to perform all of the procedures in the next sections, but first you will need to make decisions about these characteristics:

•Which packets are assigned (by DSCP value) to each queue?

•What is the size of a transmit queue relative to other queues for a given port?

•How much of the available bandwidth is allotted to each queue?

•What is the maximum rate and burst of traffic that can be transmitted out of each transmit queue?

Mapping DSCP Values to Specific Transmit Queues

To map the DSCP values to a transmit queue, perform this task:

Switch(config)# [no] qos map dscp dscp-values to 
tx-queue queue-id 

Switch(config)# end 

Switch# show qos maps dscp tx-queues

This example shows how to map DSCP values to transit queue 2.

Switch# configure terminal 

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)# qos map dscp 50 to tx-queue 2

Switch(config)# end 

Switch# 

This example shows how to verify the configuration.

Switch# show qos maps dscp tx-queue

DSCP-TxQueue Mapping Table (dscp = d1d2)

d1 :d2  0  1  2  3  4  5  6  7  8  9 

-------------------------------------

0 :   02 02 02 01 01 01 01 01 01 01 

1 :   01 01 01 01 01 01 02 02 02 02 

2 :   02 02 02 02 02 02 02 02 02 02 

3 :   02 02 03 03 03 03 03 03 03 03 

4 :   03 03 03 03 03 03 03 03 04 04 

5 :   04 04 04 04 04 04 04 04 04 04 

6 :   04 04 04 04 

Switch# 

Allocating Bandwidth Among Transmit Queues

To configure the transmit queue bandwidth, perform this task:

Switch(config)# interface gigabitethernet 
slot/interface

Switch(config-if)# tx-queue queue_id

Switch(config-if-tx-queue)# [no] [bandwidth rate 
| percent percent]

Switch(config-if-tx-queue)# end 

Switch# show qos interface

The bandwidth rate varies with the interface.

Bandwidth can only be configured on these interfaces:

•Uplink ports on Supervisor Engine III (WS-X4014)

•Ports on the WS-X4306-GB module

•The 2 1000BASE-X ports on the WS-X4232-GB-RJ module

•The first 2 ports on the WS-X4418-GB module

•The two 1000BASE-X ports on the WS-X4412-2GB-TX module

This example shows how to configure the bandwidth of 1 Mbps on transmit queue 2.

Switch# configure terminal 

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)# interface gigabitethernet 1/1 

Switch(config-if)# tx-queue 2

Switch(config-if-tx-queue)#bandwidth 1000000

Switch(config-if-tx-queue)# end 

Switch# 

Configuring Traffic Shaping of Transmit Queues

To guarantee that packets transmitted from a transmit queue do not exceed a specified maximum rate, perform this task:

Switch(config)# interface {fastethernet | 
gigabitethernet} slot/interface

Switch(config-if)# tx-queue queue_id

Switch(config-if-tx-queue)# [no] [shape rate | 
percent percent]

Switch(config-if-tx-queue)# end 

Switch# show qos interface

This example shows how to configure the shape rate to 1 Mbps on transmit queue 2.

Switch# configure terminal 

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)# interface gigabitethernet 1/1

Switch(config-if-tx-queue)# tx-queue 2

Switch(config-if-tx-queue)# shape 1000000

Switch(config-if-tx-queue)# end 

Switch# 

Configuring a High Priority Transmit Queue

To configure transmit queue 3 at a higher priority, perform this task:

Switch(config)# interface {fastethernet | 
gigabitethernet} slot/interface

Switch(config-if)# tx-queue 3

Switch(config-if)# [no] priority high

Switch(config-if)# end 

Switch# show qos interface

This example shows how to configure transmit queue 3 to high priority.

Switch# configure terminal 

Enter configuration commands, one per line.  End with CNTL/Z.

Switch(config)# interface gigabitethernet 1/1

Switch(config-if-tx-queue)# tx-queue 3

Switch(config-if-tx-queue)# priority high

Switch(config-if)# end 

Switch# 

Configuring DSCP Maps

The following sections describes how to configure the DSCP maps. It contains this configuration information:

•Configuring the CoS-to-DSCP Map

•Configuring the Policed-DSCP Map

•Configuring the DSCP-to-CoS Map

All the maps are globally defined and are applied to all ports.

Configuring the CoS-to-DSCP Map

You use the CoS-to-DSCP map to map CoS values in incoming packets to a DSCP value that QoS uses internally to represent the priority of the traffic.

Table 27-4 shows the default CoS-to-DSCP map.

If these values are not appropriate for your network, you need to modify them.

To modify the CoS-to-DSCP map, perform this task:

Switch# configure terminal

Switch(config)# qos map cos cos1 ... cos8 
to dscp dscp

Switch(config)# end

Switch# show qos maps cos-dscp

Switch# copy running-config startup-config

To return to the default map, use the no qos cos to dscp global configuration command.

This example shows how to modify and display the CoS-to-DSCP map:

Switch# configure terminal

Switch(config)# qos map cos 0 to dscp 20

Switch(config)# end

Switch# show qos maps cos dscp

CoS-DSCP Mapping Table:

CoS:  0   1  2  3  4  5  6  7 

--------------------------------

DSCP: 20  8 16 24 32 40 48 56

Switch(config)#

Configuring the Policed-DSCP Map

You use the policed-DSCP map to mark down a DSCP value to a new value as the result of a policing and marking action.

The default policed-DSCP map is a null map, which maps an incoming DSCP value to the same DSCP value.

To modify the CoS-to-DSCP map, perform this task:

Switch# configure terminal

Switch(config)# qos map dscp policed 
dscp-list to dscp mark-down-dscp

Switch(config)# end

Switch# show qos maps dscp policed

Switch# copy running-config startup-config

To return to the default map, use the no qos dscp policed global configuration command.

This example shows how to map DSCP 50 to 57 to a marked-down DSCP value of 0:

Switch# configure terminal

Switch(config)# qos map dscp policed 50 51 52 53 54 55 56 57 to dscp 0

Switch(config)# end

Switch# show qos maps dscp policed

Policed-dscp map:

     d1 :  d2 0  1  2  3  4  5  6  7  8  9

     ---------------------------------------

      0 :    00 01 02 03 04 05 06 07 08 09

      1 :    10 11 12 13 14 15 16 17 18 19

      2 :    20 21 22 23 24 25 26 27 28 29

      3 :    30 31 32 33 34 35 36 37 38 39

      4 :    40 41 42 43 44 45 46 47 48 49

      5 :    00 00 00 00 00 00 00 00 58 59

      6 :    60 61 62 63

Note In the above policed-DSCP map, the marked-down DSCP values are shown in the body of the matrix. The d1 column specifies the most-significant digit of the original DSCP; the d2 row specifies the least-significant digit of the original DSCP. The intersection of the d1 and d2 values provides the marked-down value. For example, an original DSCP value of 53 corresponds to a marked-down DSCP value of 0.

Configuring the DSCP-to-CoS Map

You use the DSCP-to-CoS map to generate a CoS value.

Table 27-5 shows the default DSCP-to-CoS map.

If the values above are not appropriate for your network, you need to modify them.

To modify the DSCP-to-CoS map, perform this task:

Switch# configure terminal

Switch(config)# qos map dscp dscp-list 
to cos cos

Switch(config)# end

Switch# show qos maps dscp to cos

Switch# copy running-config 
startup-config

To return to the default map, use the no qos dscp to cos global configuration command.

This example shows how to map DSCP values 0, 8, 16, 24, 32, 40, 48, and 50 to CoS value 0 and to display the map:

Switch# configure terminal

Switch(config)# qos map dscp 0 8 16 24 32 40 48 50 to cos 0

Switch(config)# end

Switch# show qos maps dscp cos

Dscp-cos map:

     d1 :  d2 0  1  2  3  4  5  6  7  8  9

     ---------------------------------------

      0 :    00 00 00 00 00 00 00 00 00 01

      1 :    01 01 01 01 01 01 00 02 02 02

      2 :    02 02 02 02 00 03 03 03 03 03

      3 :    03 03 00 04 04 04 04 04 04 04

      4 :    00 05 05 05 05 05 05 05 00 06

      5 :    00 06 06 06 06 06 07 07 07 07

      6 :    07 07 07 07

Note In the above DSCP-to-CoS map, the CoS values are shown in the body of the matrix. The d1 column specifies the most-significant digit of the DSCP; the d2 row specifies the least-significant digit of the DSCP. The intersection of the d1 and d2 values provides the CoS value. For example, in the DSCP-to-CoS map, a DSCP value of 08 corresponds to a CoS value of 0.