20-6
Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter 20 Configuring QoS
Understanding QoS
Figure 20-3 Classification Flowchart
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Generate the DSCP
based on IP precedence
in packet. Use the
IP-precedence-to-DSCP map.
Assign default
port CoS.
Yes
Yes
No
No
No
Yes
No
(Optional) Modify the
DSCP by using the
DSCP-to-DSCP-mutation
map.
Read ingress interface
configuration for classification.
Assign DSCP identical
to DSCP in packet.
Check if packet came
with CoS label (tag).
Generate DSCP from
CoS-to-DSCP map.
Yes
Read next ACL. Is there
a match with a "permit" action?
Assign the DSCP as
specified by ACL action.
Assign the default
DSCP (0).
Are there any (more) QoS ACLs
configured for this interface?
Check if packet came
with CoS label (tag).
Use Cos
from frame.
Start
Trust CoS (IP and non-IP traffic).
IP and
non-IP
traffic
Use port
default
(non-IP traffic).
Trust IP
precedence
(IP traffic).
Trust DSCP (IP traffic).
Done
Done
Done
Done
Assign the default port
CoS and generate a
DSCP from the
CoS-to-DSCP map.
Generate the DSCP by using
the CoS-to-DSCP map.
