Cisco WS-C6506 Software Manual page 1243

Chapter 52 Configuring QoS
PFC3A/PFC3B/PFC3BXL provides QoS for the ingress and egress traffic. PFC2 and PFC provide QoS
only for the ingress traffic.
With PFC3, QoS supports map-based egress DSCP mutation, which allows you to remark the egress
traffic after it has been subjected to a policing rule, and the option to preserve the received DSCP in the
egress traffic.
The ACLs contain the access control entries (ACEs) that specify the Layer 2, 3, and 4 classification
criteria, a marking rule, and policers. Marking sets the Layer 3 IP precedence or DSCP values and the
Layer 2 CoS value to either the received or configured Layer 2 or Layer 3 values. Policing uses
bandwidth limits to either drop or mark the nonconforming traffic. For more information, see the
"Classification, Marking, and Policing with a Layer 3 Switching Engine" section on page
During processing, a Layer 3 switching engine associates a DSCP value with all traffic, including non-IP
traffic. For more information, see the
Layer 2 Switching Engine Features
With a Layer 2 Switching Engine, QoS can classify traffic using the Layer 2 destination MAC addresses,
VLANs, and marking using the Layer 2 CoS values. Classification and marking with a Layer 2
Switching Engine do not use or set the Layer 3 IP precedence or DSCP values. For more information,
see the
on page
Ethernet Egress Port Features
With any switching engine, QoS supports Ethernet egress port scheduling and congestion avoidance
using the Layer 2 CoS values. Ethernet egress port marking sets the Layer 2 CoS values and, with a
Layer 3 switching engine, the Layer 3 DSCP values. For more information, see the
Scheduling, Congestion Avoidance, and Marking" section on page
Single-Port ATM OC-12 Switching Module Features
The ingress interface from a single-port ATM OC-12 switching module is untrusted, and QoS sets CoS
to zero in all traffic that is received from it. With a Layer 3 switching engine, QoS can mark the IP traffic
that is transmitted to a single-port ATM OC-12 switching module with the Layer 3 DSCP values.
Multilayer Switch Feature Card (MSFC, MSFC2, or MSFC3)
QoS marks the IP traffic that is transmitted to an MSFC with the Layer 3 DSCP values. The CoS is zero
in all traffic that is sent from an MSFC to the egress ports.
The traffic that is Layer 3 switched does not go through the MFSC and retains the CoS value that is
Note
assigned by the Layer 3 switching engine.
OL-8978-04
"Classification and Marking on a Supervisor Engine 1 with a Layer 2 Switching Engine" section
52-28.
"Internal DSCP Values" section on page
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
Understanding How QoS Works
52-15.
52-16.
"Ethernet Egress Port
52-28.
52-11