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scheduling on Layer 2 (L2) ports. Refer to the document Installation and Configuration Note
for the Catalyst 4000 Layer 3 Services Module for additional features that are available on
Layer 3 (L3) Gigabit Ethernet interfaces.
Q. What is the minimum software that is necessary for QoS on Catalyst
4500/4000 switches that run CatOS?
A. You need Supervisor Engine software version 5.4(2) and later on the Catalyst 4500/4000
(Supervisor Engine I and Supervisor Engine II), Catalyst 2948G, Catalyst 2980G, and
Catalyst 4912G to support the QoS features.
Q. Do the Catalyst 4500/4000 switches that run CatOS support
rate−limiting or policing on ports or VLANs?
A. Catalyst 4500/4000 switches that run CatOS do not provide policing or rate−limiting on
Layer 2 (L2) ports. Rate−limiting is supported on Layer 3 (L3) Gigabit Ethernet interfaces.
Refer to the Installation and Configuration Note for the Catalyst 4000 Layer 3 Services
Module for additional information. Policing is supported on the Catalyst 4500/4000 switches
that run Cisco IOS Software. For more information, refer to the document QOS Policing and
Marking with Catalyst 4000/4500 IOS−Based Supervisor Engines.
Q. Can the Catalyst 4500/4000 switches that run CatOS mark or rewrite IP
precedence Type of Service (ToS) bits in an IP packet?
A. Catalyst 4500/4000 switches that run CatOS do not provide Layer 3 (L3) marking or
rewriting on Layer 2 (L2) ports. The L3 ToS bits of an incoming packet are passed through
the L2 switch untouched. The incoming IP precedence on L3 module Gigabit Ethernet
interfaces is honored. Refer to the Installation and Configuration Note for the Catalyst 4000
Layer 3 Services Module for additional information. Marking and rewriting of IP
precedence/differentiated services code point (DSCP) is supported in a Catalyst 4500/4000
that runs Cisco IOS Software. For more information, refer to the document QOS Policing and
Marking with Catalyst 4000/4500 IOS−Based Supervisor Engines.
Q. What kind of input scheduling do the Catalyst 4500/4000 switches that
run CatOS provide?
A. Line cards of Catalyst 4500/4000 switches that run CatOS have FIFO input scheduling on
Layer 2 (L2) ports. Refer to the Installation and Configuration Note for the Catalyst 4000
Layer 3 Services Module for additional information on Layer 3 (L3) module features.
Q. Can the Catalyst 4500/4000 switches that run CatOS change the
incoming Class of Service (CoS) value in IEEE 802.1Q (dot1q) tags?
A. No. The Catalyst 4500/4000 switches that run CatOS support frame classification and
marking only on unclassified frames entering the switch and cannot change CoS values on
already tagged packets. Catalyst 4500/4000 switches that run Cisco IOS Software can classify
or reclassify tagged/untagged packets. For more information, refer to the document
Understanding and Configuring QoS.
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