41-5
Catalyst 6000 Family Software Configuration Guide—Releases 6.3 and 6.4
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Chapter 41 Configuring QoS
Understanding How QoS Works
Figure 41-3 Layer 3 Switching Engine Classification, Marking, and Policing
Yes
No
No
No
No
Yes
From ingress
port or VLAN
IP
Packet?
ACL(s)
on
interface?
1
Trust
received
DSCP?
Out of
profile?
No
Policing
rule in
ACE?
Drop
packet
1
Trust
received IP
precedence?
2
Set DSCP
from received
IP precedence
No
No
Yes
Yes
Markdown?
3
Set DSCP
from received
or port CoS
Use DSCP
from
ACE
4
Set DSCP
to marked
down value
Use default
ACL
To egress
interface
Yes
No
No
Match
ACE in ACL?
Yes
Yes
Yes
Yes
25041
L3 Switching Engine (PFC) classification, marking, and policing
1
Traffic is from
an untrusted
port
1
Trust
received or port
CoS?
Use received
DSCP
2
Specified by AC
E
keyword or by
port keyword and
dscp
AC
E
keyword
3
From IP precedence-to-DSCP map
4
From CoS-to-DSCP map
5
F
From DSCP-to-CoS map
1
rom DSCP markdown map
5
Derive CoS
from DSCP