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Catalyst 6500 Series Switch Software Configuration Guide—Release 8.7
OL-8978-04
Chapter 52 Configuring QoS
Understanding How QoS Works
Marking Rules
Note PFC2 cannot not mark IPX or MAC traffic. PFC3 does not provide QoS for IPX traffic.
The marking rules specify how QoS marks the traffic when the traffic matches the filtering parameters
in an ACE (see the “ACE Name, Marking Rule, Policing, and Filtering Syntax” section on page 52-46).
QoS supports four marking rules that are specified with the following four ACE keywords: trust-dscp,
trust-ipprec, trust-cos, and dscp. Each ACE contains one of the keywords.
The marking rules are as follows:
• trust-dscp (IP ACLs only)—Instructs QoS to set the internal and egress DSCP from the received
DSCP values (see the “Internal DSCP Values” section on page 52-16).
• trust-ipprec (IP ACLs only)—Instructs QoS to set the internal and egress DSCP from the received
IP precedence values.
Note With the trust-ipprec port keyword, QoS uses only the IP precedence bits. If the traffic with
a DSCP value enters the switch through a port that is configured with the trust-ipprec port
keyword, the three most significant bits of the DSCP value are interpreted as an IP
precedence value; QoS ignores the rest of the DSCP value.
• trust-cos (all ACLs except IPX and MAC with PFC2 and IPX with PFC3)—Instructs QoS to set the
internal and egress DSCP from the received or port CoS values. In the traffic from the ports that are
configured with the trust-cos keyword, QoS uses the CoS value that is received in the ISL and
802.1Q frames; in all other cases, QoS uses the CoS value that is configured on the port (default is
zero).
• dscp (all ACLs except IPX and MAC with PFC2 and IPX with PFC3)—Instructs QoS to mark the
traffic as indicated by the port trust keywords:
–
In the IP traffic from the ingress ports that are configured with the trust-dscp port keyword, the
dscp ACE keyword instructs QoS to set the internal and egress DSCP values from the received
DSCP values. In the non-IP traffic, QoS sets the DSCP from the received or port CoS value.
–
In the IP traffic from the ingress ports that are configured with the trust-ipprec port keyword,
the dscp ACE keyword instructs QoS to set the internal and egress DSCP values from the
received IP precedence values. In the non-IP traffic, QoS sets the DSCP value from the received
or port CoS value.
–
In the traffic from the ingress ports that are configured with the trust-cos port keyword, the dscp
ACE keyword instructs QoS to set the internal and egress DSCP values from the received or port
CoS values.
–
In the traffic from the ingress ports that are configured with the untrusted port keyword, the
dscp ACE keyword instructs QoS to set the internal and egress DSCP values from the DSCP
value in the ACE.
Note The default configuration of the ACEs in the default ACLs contains the dscp ACE keyword,
which supports the per-port classification of the traffic. With the default values, the ACEs in
the default ACLs apply DSCP zero to the traffic from the ingress ports that are configured
with the untrusted port keyword.
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