Previous chapters described the necessity for QoS in campus networks and the fundamentals behind QoS operation. This chapter explains the various platform QoS features available across the Cisco Catalyst product family. A group of concise tables in the beginning of this chapter provides a quick reference for QoS features available for each Catalyst platform. In addition, this chapter, along with subsequent chapters, begins the product tour of the access layer Catalyst switches with the fewest QoS features and continues with the high-end core Catalyst switches with industry-leading QoS features. Although the access layer switches support only a few QoS features, these switches provide an excellent foundation for exploring QoS fundamentals in the campus network.
Specifically, this chapter covers the following topics:
Brief Per–Catalyst Platform QoS Features Table
QoS Features Overview
QoS Features on the Catalyst 2900XL and 3500XL Switches
QoS Features on the Catalyst 4000 CatOS Switches
The Cisco Catalyst 2900XL, 3500XL, and 4000 Family of switches share Layer 2 QoS features needed on access layer switches. These features include the following:
Classification
Marking
Congestion Management
This chapter covers these topics on the respective platforms with command references, examples, and case studies. Upon completion of this chapter, you will understand each Catalyst platform's supported QoS features and be able to configure the Catalyst 2900XL, 500XL, and 4000 CatOS Family of switches for packet classification, marking, and congestion management.
From a platform perspective, the Catalyst 4000 CatOS Family of switches must be distinguished from the Catalyst 4000 Cisco IOS Family of switches due to individual differences in QoS features and configuration. The supervisor engine model determines whether a Catalyst 4000 switch operates on CatOS or Cisco IOS. In addition, the Catalyst 4000 Layer 3 services module also has exclusive Layer 3 QoS features (discussed in Chapter 7, "Advanced QoS Features Available on the Catalyst 4000 IOS Family of Switches and the Catalyst G-L3 Family of Switches"). This chapter is only applicable to the Catalyst 4000 CatOS switches. Table 3-8 shows which Catalyst 4000 switches are applicable to this chapter.
Catalyst Feature Overview
Cisco Catalyst switches support a wide range of QoS features. Generally, the high-end platforms support more QoS features especially platforms that support Layer 3 IP routing. Tables 3-1 through 3-5 provide a quick reference for QoS features for each platform. All platforms may have limitations and caveats per feature, and each QoS feature is discussed in the appropriate chapter of this book in additional detail.
Furthermore, QoS features are also dependent on whether the platform supports IP routing. The Catalyst 3550, Catalyst 4000 Cisco IOS Software family, Catalyst 5500 with Route Switch Module (RSM) or Router Switch Feature Card (RSFC), and the Catalyst 6000/6500 with Multilayer Switch Module (MSM) or Multilayer Switch Feature Card (MSFC) I/II support IP routing. Other platforms may support Layer 3 QoS features, such as classification based on differentiated services codepoint (DSCP) and marking of IP precedence; however, these platforms do not actually support routing of IP frames. As a result, network designs do not require platforms that support IP routing to classify, mark, police, or schedule traffic based on DSCP or IP precedence values. Therefore, network designers may choose lower-cost switches that do not support IP routing to enable Layer 3 QoS features.
The next sections provide quick reference tables for supported QoS features per platform. The tables only provide a glimpse into QoS feature support of each platform and do not indicate the benefits or restrictions of each feature. Refer to the appropriate chapters later in this book for thorough discussions of QoS feature support on each platform.
Specifically, the next sections highlight the following QoS features supported on each platform:
Input Scheduling
Policing
Classification and Marking
Output Scheduling
Table 3-1 indicates at a simplistic level, QoS feature support on a per-platform basis for most of the currently shipping Catalyst switches. The table only indicates at the fundamental level where a feature is supported and does not indicate the restrictions or caveats.
Table 3-1 QoS Feature Overview on Current Catalyst Switches
|
Product Family |
Classification |
Marking |
Policing |
Congestion Management |
Congestion Avoidance |
|
2950 |
Yes |
Yes |
Yes |
Yes |
No |
|
3550 |
Yes |
Yes |
Yes |
Yes |
Yes |
|
4000 IOS Family |
Yes |
Yes |
Yes |
Yes |
No |
|
6500 Family |
Yes |
Yes |
Yes |
Yes |
Yes |
Input Scheduling
Input scheduling is currently available only on the Catalyst 6000/6500. Input scheduling priorities and schedules packets out of ingress packet queues based on several QoS values including CoS and DSCP. However, most of Catalyst switches can deliver packets to the switching fabric at line rate or a specified rate. This specific rate defines the maximum throughput of the switch. If the input rate is not exceeded, input scheduling is not crucial in implementing QoS architecture. Furthermore, ingress policing is an option on many Catalyst switches that aids in preventing oversubscription of the switch fabric by limiting ingress traffic. Table 3-2 summarizes Catalyst platform support for input scheduling. The Comments column also denotes any switch capable of ingress policing.
Table 3-2 Catalyst Platform QoS Input Scheduling Support
|
Catalyst Switch |
Input Scheduling |
Ingress Policing |
Comments |
|
Catalyst 2900XL |
No |
No |
Switching fabric is capable of 1.6 Gbps ingress. |
|
Catalyst 2948G-L3/ 4912G-L3/4232-L3 |
No |
Yes |
|
|
Catalyst 2950 |
No |
Yes |
|
|
Catalyst 3500XL |
No |
No |
Switching fabric is capable of 5.0 Gbps ingress. |
|
Catalyst 3550 |
No |
Yes |
|
|
Catalyst 4000 CatOS Family |
No |
No |
Nonblocking line cards can deliver ingress traffic at line rate to switching fabric |
|
Catalyst 4000 Cisco IOS Family (Supervisor III and IV) |
No |
Yes |
Non-blocking linecards can deliver ingress traffic at line rate to switching fabric. |
|
Catalyst 5500 |
No |
No |
|
|
Catalyst 5500 w/NFFC1 II |
No |
No |
|
|
Catalyst 6000/6500 |
Yes |
Yes |
Based on Layer 2 CoS2; option for ingress Priority Queue. |
Classification and Marking
Classification and marking support and features vary per switch. Table 3-3 indicates which platforms support specific classification and marking features. All switches that support QoS also support classification based on CoS values. Current generation switches that support IP routing also support classification and marking using IP precedence or DSCP values in addition to classification and marking of CoS values.
Table 3-3 Catalyst Platform QoS Classification and Marking Support
|
Catalyst Switch |
Classification Marking of Untagged Frames |
Marking CoS on Tagged Frames |
Marking DSCP on Tagged Frames |
Classification Based on DSCP of Ingress Frames |
|
Catalyst 2900XL |
Yes |
No |
No |
No |
|
Catalyst 2948G-L3/4912G-L3/4232-L3 |
No |
No |
No |
No, IP precedence only |
|
Catalyst 2950 |
No, IP precedence only |
Yes |
Yes |
Yes |
|
Catalyst 3500XL |
Yes |
Yes, on specific models |
No |
No |
|
Catalyst 3550 |
Yes |
Yes |
Yes |
Yes |
|
Catalyst 4000 CatOS Family |
Yes |
Yes |
No |
No |
|
Catalyst 4000 Cisco IOS Family (Supervisor III and IV) |
Yes |
Yes |
Yes |
Yes |
|
Catalyst 5500 |
Yes, requires NFFC II |
Yes, requires NFFC II |
Yes, requires NFFC II |
Yes, requires NFFC II |
|
Catalyst 6500 |
Yes |
Yes |
Yes |
Yes |
Policing
Table 3-4 indicates which Catalyst platforms support policing. Feature support and platform implementation of policing varies between each Catalyst switch. Three types of policing exist for Catalyst platforms:
Individual policing
Aggregate policing
Microflow policing
Individual policing applies the bandwidth limit of a policer per interface. For example, an individual policer configured to constrain ingress traffic to 32 kbps limits each applicable interface to 32 kbps on ingress. An aggregate policer configured for the same bandwidth constraint limits the bandwidth collectively among all interfaces. Microflow policing is available on the Catalyst 6500, and it applies bandwidth limits to each access-control entry (ACE) of a defined policer. Chapter 8, "QoS Support on the Catalyst 6500," discusses ACEs and microflow policing in more detail.
Each platform has unique support, restrictions, and requirements surrounding policing. Refer to each product chapter for specifics.
Table 3-4 Catalyst Platform QoS Policing Support
|
Cisco Catalyst Platform |
Ingress Policing |
Egress Policing |
Individual Policing |
Aggregate Policing |
Microflow Policing |
|
Catalyst 2900XL |
No |
No |
No |
No |
No |
|
Catalyst 2948G-L3/4912G-L3/4232-L3 |
Yes, per-port rate-limiting |
Yes, per port rate-limiting and traffic shaping |
No |
No |
No |
|
Catalyst 2950 |
Yes |
No |
Yes |
No |
No |
|
Catalyst 3500XL |
No |
No |
No |
No |
No |
|
Catalyst 3550 |
Yes |
Yes |
Yes |
Yes |
No |
|
Catalyst 4000 CatOS Family |
No |
No |
No |
No |
No |
|
Catalyst 4000 Cisco IOS Family (Supervisor III and IV) |
Yes |
Yes |
Yes |
Yes |
No |
|
Catalyst 5500 w/NFFC II |
No |
No |
No |
No |
No |
|
Catalyst 6500 |
Yes |
No |
No |
Yes |
Yes |
Congestion Management
Congestion management is supported on all Catalyst switches that support QoS features. Congestion avoidance and management is achieved via the use of output scheduling using the tail-drop and Weighted Random Early Detection (WRED) queuing mechanisms. Chapter 2, "End-to-End QoS: Quality of Service at Layer 3 and Layer 2," explains the difference between congestion management and congestion avoidance, and later chapters explain the tail-drop and WRED queuing mechanisms in the congestion avoidance section of each chapter where applicable. Moreover, only the Catalyst 3550, Catalyst 4000 IOS Family of switches, and the Catalyst 6500 support congestion avoidance.
The nomenclature for output scheduling queues is a follows:
XpYqZt
X indicates the number of strict-priority queues.
Y indicates the number of queues other than strict-priority queues.
Z indicates the configurable thresholds per queue.
For example, 1p3q2t indicates that a switch has an egress output queue with one strict-priority queue and three normal-priority queues each with two configurable thresholds per queue.
Table 3-5 indicates the available output queues per platform.
Table 3-5 Catalyst Platform Congestion Management Support
|
Cisco Catalyst Platform |
Output Scheduling |
Scheduling Queues |
|
Catalyst 2900XL |
Yes |
Global 2q1t |
|
Catalyst 2948G-L3/4912G-L3/4232-L3 |
Yes |
4q |
|
Catalyst 2950 |
Yes |
4q |
|
Catalyst 3500XL |
Yes |
Global 2q1t |
|
Catalyst 3550 |
Yes |
1p3q2t, 4q4t |
|
Catalyst 4000 CatOS Family |
Yes |
2q1t |
|
Catalyst 4000 Cisco IOS Family (Supervisor III and IV) |
Yes |
1p3q1t, 4q1t |
|
Catalyst 5500 w/NFFC II |
Yes |
1q4t |
|
Catalyst 6500 |
Yes |
Ingress: 1q4t, 1p1q4t, 1p1q, 1p2q1t Egress: 2q2t, 1p2q2t, 1p3q1t, 1p2q1t, 1p1q8t, and 1p1q0t |