82 Chapter 3: Overview of QOS Support on Catalyst Platforms
QoS Support on the Catalyst 4000 CatOS Family of
Switches
Catalyst 4000 CatOS switches provide for QoS classification and congestion management
solely based on CoS values. The Catalyst 4000 IOS switches, discussed in Chapter 7,
support a wider range of QoS. For the Catalyst 4000 CatOS switches, a high- and low-
priority transmit port queue with round-robin scheduling accomplish congestion
management. The Catalyst 4000 CatOS switches do not support policing or input sched-
uling. The following sections discuss the Catalyst 4000 CatOS QoS features with detailed
overviews, configuration guidelines, and examples.
Catalyst 4000 Product Family Delineation
This section covers the Catalyst 4000 CatOS Family of switches. As discussed in the intro-
duction to this chapter, the Catalyst 4000 Cisco IOS switches, the Catalyst 4000 CatOS
switches, and the Layer 3 services module each have unique QoS feature support. The
Catalyst 4000 Cisco IOS switches and the Layer 3 services module are covered in Chapter 7.
Table 3-8 summarizes the Catalyst 4000 switches into the CatOS or IOS category. This
chapter applies to the Catalyst 4000 switches that run CatOS Software.
Table 3-8 Catalyst 4000 CatOS Versus Cisco IOS Software Platform Support
Catalyst 4000 Model Family Description Software
Catalyst 2948G Catalyst 4000 48-port 10/100BASE-TX switch ports + 2
1000BASE-X GBIC* switch ports
CatOS
Catalyst 2980G Catalyst 4000 80-port 10/100BASE-TX switch ports + 2
1000BASE-X GBIC switch ports
CatOS
Catalyst 2980G-A Catalyst 4000 80-port 10/100BASE-TX switch ports + 2
1000BASE-X GBIC switch ports
CatOS
Catalyst 2948G-L3 Catalyst G-L3 48-port 10/100BASE-TX + 2 1000BASE-X
GBIC Layer 3 switch
IOS
Catalyst 4003 + WS-X4012
Supervisor I Engine
Catalyst 4000 3-slot modular chassis + 2 1000BASE-X GBIC
ports on Layer 2 supervisor
CatOS
Catalyst 4006 + WS-X4013
Supervisor II Engine
Catalyst 4000 6-slot modular chassis + 2 1000BASE-X GBIC
ports on Layer 2 supervisor
CatOS
Catalyst 4006 + WS-X4014
Supervisor III Engine
Catalyst 4000 6-slot modular chassis + 2 1000BASE-X GBIC
ports on Layer 2/3 supervisor
IOS
Catalyst 4006 + WS-X4515
Supervisor IV Engine
Catalyst 4000 6-slot modular chassis + 2 1000BASE-X GBIC
ports on Layer 2/3 supervisor
IOS
Catalyst WS-X4232-L3
Layer 3 Services Module
Catalyst G-L3 Layer 3 router module for Catalyst 4003 and
4006 chassis with Supervisor I or II Engine
IOS
QoS Support on the Catalyst 4000 CatOS Family of Switches 83
*GBIC Gigabit Interface Converter
Catalyst 4000 CatOS Family of Switches QoS Architectural Overview
The Catalyst 4000 CatOS switches support only QoS classification, marking, and
congestion management. Classification and marking is based on the CoS value of 802.1q
frames and port trust. Using two transmit queues for output scheduling achieves congestion
management of egress traffic. Input scheduling is limited to first-in, first-out (FIFO) ingress
queuing only. Figure 3-5 shows the basic QoS model for the Catalyst CatOS switches.
Software Requirements
The Catalyst 4000 CatOS switches require CatOS Software version 5.2(1) or higher for
QoS feature support.
Enabling QoS Features on Catalyst 4000 CatOS Switches
QoS must be globally enabled on CatOS switches before classification, marking, and
output scheduling configurations are applied. To enable QoS on the Catalyst 4000 CatOS
switches, enter the following command:
set qos {enable | disable}
Catalyst 4000 Model Family Description Software
Catalyst 4503 + WS-X4013
Supervisor II Engine
Catalyst 4000 3-slot modular chassis + 2 1000BASE-X GBIC
ports on Layer 2 supervisor
CatOS
Catalyst 4503 + WS-X4014
Supervisor III Engine
Catalyst 4000 3-slot modular chassis + 2 1000BASE-X GBIC
ports on Layer 2/3 supervisor
IOS
Catalyst 4503 + WS-X4515
Supervisor IV Engine
Catalyst 4000 3-slot modular chassis + 2 1000BASE-X GBIC
ports on Layer 2/3 supervisor
IOS
Catalyst 4506 + WS-X4013
Supervisor III Engine
Catalyst 4000 6-slot modular chassis + 2 1000BASE-X GBIC
ports on Layer 2 supervisor
CatOS
Catalyst 4506 + WS-X4014
Supervisor III Engine
Catalyst 4000 6-slot modular chassis + 2 1000BASE-X GBIC
ports on Layer 2/3 supervisor
IOS
Catalyst 4506 + WS-X4515
Supervisor IV Engine
Catalyst 4000 6-slot modular chassis + 2 1000BASE-X GBIC
ports on Layer 2/3 supervisor
IOS
Catalyst 4507R + WS-X4515
Supervisor IV Engine
Catalyst 4000 7-slot modular chassis + 2 1000BASE-X GBIC
ports on Layer 2/3 supervisor
IOS
Catalyst 4840G Catalyst G-L3 40-port 10/100BASE-TX + 1000BASE-X GBIC
Layer 3 server load-balancing switch
IOS
Catalyst 4908G-L3 Catalyst 4000 8 1000BASE-X GBIC Layer 3 switch CatOS
Catalyst 4912G-L3 Catalyst G-L3 8 1000BASE-X GBIC switch ports IOS
Table 3-8 Catalyst 4000 CatOS Versus Cisco IOS Software Platform Support (Continued)
84 Chapter 3: Overview of QOS Support on Catalyst Platforms
Figure 3-5 Basic QoS Architecture for the Catalyst Cat4000 CatOS Switches
Example 3-4 shows a user enabling QoS on a CatOS switch.
Input Scheduling
Similar to other access layer switches, the Catalyst 4000 CatOS switches performs only
FIFO Queuing of ingress packets. For line-module ports that are nonblocking, FIFO
Queuing does not pose an issue because nonblocking line-module ports can deliver traffic
to the switching fabric at line rate. Ports that are oversubscribed to the switching fabric are
also referred to as blocking ports. Oversubscribed ports share bandwidth and data transmit
contention in groups of two to eight ports depending on line module. Campus network
design must consider oversubscribed ports very carefully on the Catalyst 4000 because of
the lack of input scheduling. Furthermore, when using the nonblocking modules, consider
Example 3-4 Enabling QoS Features on a Catalyst 4000 CatOS Switch
Console> (enable) set qos enable
QoS is enabled.
Console> (enable)
L2 Lookup
Configured
CoS Map
Place Packet in
Port Low Priority
Queue
Place Packet in
Port High Priority
Queue
Round-Robin
Schedule
Transmit Packet
HighLow
Classification
Packet Enters
Global Queue
QoS Support on the Catalyst 4000 CatOS Family of Switches 85
aligning the front panels to minimize oversubscription. For example, avoid placing
workstations utilizing real-time voice and video applications on the same group of ports
that share oversubscribed bandwidth with high-traffic servers and network appliances. The
product release notes contain detailed information on which ports share bandwidth.
Moreover, all line-module ports support 802.1x flow control for constraining host traffic.
802.1x flow control is useful in limiting traffic for hosts connected to oversubscribed ports.
Table 3-9 lists the available line modules at the time of publication and denotes whether the
ports are blocking or nonblocking. Several line modules are both nonblocking and blocking
depending on the front-panel port. The table also describes how the ports are subscribed to
the switching fabric.
Table 3-9 Catalyst 4000 Line Modules Architecture
Module
Ethernet Ports
(Media Type) Architecture to Switch Fabric
WS-U4504-FX-MT 4 100BASE-FX (MTRJ) Nonblocking.
WS-X4012 2 1000BASE-X (GBIC) Nonblocking.
WS-X4013 2 1000BASE-X (GBIC) Nonblocking.
WS-X4014 2 1000BASE-X (GBIC) Nonblocking.
WS-X4515 2 1000BASE-X (GBIC) Nonblocking.
WS-X4124-FX-MT 24 100BASE-FX (MTRJ) Nonblocking.
WS-X4148-FX-MT 48 100BASE-FX (MTRJ) Nonblocking.
WS-X4148-RJ21 48-port 10/100BASE-TX (RJ21) Nonblocking.
WS-X4148-RJ45 48-port 10/100BASE-TX (RJ45) Nonblocking.
WS-X4148-RJ45V 48-port 10/100BASE-TX with Inline
Power (RJ45)
Nonblocking.
WS-X4306-GB 6 1000BASE-X (GBIC) Nonblocking.
WS-X4232-GB-RJ 32-port 10/100BASE-TX (RJ45) +
2 1000BASE-X (GBIC)
Nonblocking.
WS-X4232-L3 32, L2 10/100BASE-TX L2 (RJ45) +
2 L3 1000BASE-X (GBIC)
32 10/100BASE-TX ports are nonblocking.
WS-X4412-2GB-T 12-port 1000BASE-T (RJ45) +
2 1000BASE-X (GBIC)
The 2 1000BASE-X ports are nonblocking. The
1000BASE-T ports are group 3 front-panel ports
to a 1-gigabit switch fabric connection.
WS-X4418-2GB 18 1000BASE-X (GBIC) Front-panel ports 1 and 2 are nonblocking. Ports
3 through 18 are grouped 4 front-panel
1000BASE-X ports to a 1-gigabit switch fabric
connection.
WS-X4424-GB-RJ45 24-port 10/100/1000BASE-T (RJ45) Each consecutive group of 4 ports is connected
to a 1-gigabit switch fabric connection.
continues
86 Chapter 3: Overview of QOS Support on Catalyst Platforms
Classification, Marking, and Trusting
The Catalyst 4000 CatOS switches are unable to differentiate between trusted and untrusted
ports. As a result, the Catalyst 4000 CatOS switches consider all ports trusted, and the
switch does not alter the CoS value for any Ethernet 802.1q tagged frames. System admin-
istrators need to be aware of servers, network appliances, or workstations that may be
inappropriately marking CoS values in transmitted 802.1q tagged frames because the incor-
rectly marked frames could effect high-priority traffic such as voice or video.
Classifying Untagged Frames
The Catalyst 4000 CatOS switch may mark untagged frames with a default CoS value. The
default CoS value is a global parameter applied to all ports for untagged frames received by
the switch. This default CoS value marking technique cannot be applied to selective ports
or selective frames. Marking is strictly a global parameter for untagged frames. To
configure the default CoS value for untagged frames, enter the following command:
set qos defaultcos
default-cos-value
default-cos-value indicates the CoS value to be marked on untagged frames.
Example 3-5 shows a user configuring a global default CoS value.
NOTE Extended trust configuration is not supported on the Catalyst 4000 CatOS switches.
The Catalyst 4000 CatOS switches support only 802.1q trunking; Inter-Switch Link (ISL)
trunking is not supported. The Catalyst 4000 Supervisor III and IV Engine both support ISL
on existing linecards with a few exceptions.
Module
Ethernet Ports
(Media Type) Architecture to Switch Fabric
WS-X4448-GB-LX 48-port 1000BASE-LX (SFP) Each consecutive group of 8 ports is connected
to a 1-gigabit switch fabric connection.
WS-X4448-GB-RJ45 48-port 10/100/1000BASE-T (RJ45) Each consecutive group of 8 ports is connected
to a 1-gigabit switch fabric connection.
Example 3-5 Defining Default CoS Value on Catalyst 4000 CatOS Switch
Console> (enable) set qos defaultcos 5
qos defaultcos set to 5
Table 3-9 Catalyst 4000 Line Modules Architecture (Continued)
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