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Understanding How QoS Works
If an excess police level is set, the excess DSCP mapping is used to replace the original DSCP value with
a marked-down value. If only a normal police level is set, the normal DSCP mapping is used. The excess
police level has precedence for selecting the mapping rules when both police levels are set because the
excess police level represents the worst out-of-profile transgression.
PFC3 Policing Decisions
In addition to PFC2 policing decisions, PFC3 supports egress QoS. These sections describe the PFC3
policing decisions:
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•
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Policing Hardware-Forwarded LAN Traffic
The hardware-forwarded LAN traffic (traffic that is forwarded by PFC3) can be subject to both an
ingress and an egress policing rule. When the LAN traffic is subject to both an ingress and an egress
policing rule, QoS evaluates both the rules simultaneously and applies the most severe rule. Because the
policing rules are evaluated simultaneously, the markdown from an ingress policing rule is never used
as the basis for the egress policing markdown.
Policing Software-Forwarded LAN Traffic
The software-forwarded LAN traffic (LAN traffic that is forwarded in the software by the MSFC) can
be subject to both an ingress and an egress policing rule. When the software-forwarded traffic is subject
to both an ingress and an egress policing rule, QoS evaluates the rules sequentially. The markdown from
an ingress policing rule can be the basis for the egress policing markdown.
Policing Software-Forwarded WAN Traffic
PFC3 can provide egress QoS for the software-forwarded WAN traffic. The software-forwarded WAN
traffic is subject only to an egress policing rule.
Attaching ACLs
You can configure each port for either port-based QoS (default) or VLAN-based QoS (see the
Port-Based or VLAN-Based QoS" section on page
(see the
ACLs, one of each type (IP, IPX, and Ethernet) to each port and VLAN.
Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
52-26
Policing Hardware-Forwarded LAN Traffic, page 52-26
Policing Software-Forwarded LAN Traffic, page 52-26
Policing Software-Forwarded WAN Traffic, page 52-26
"Attaching an ACL to an Interface" section on page
52-40) and attach the ACLs to the selected interface
52-56). You can attach up to three named
Chapter 52
Configuring QoS
"Enabling
OL-8978-04
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Troubleshooting
