33-33
Catalyst 3750 Switch Software Configuration Guide
OL-8550-02
Chapter 33 Configuring QoS
Configuring Standard QoS
Default Mapping Table Configuration
The default CoS-to-DSCP map is shown in Table 33-12 on page 33-61.
The default IP-precedence-to-DSCP map is shown in Table 33-13 on page 33-62.
The default DSCP-to-CoS map is shown in Table 33-14 on page 33-64.
The default DSCP-to-DSCP-mutation map is a null map, which maps an incoming DSCP value to the
same DSCP value.
The default policed-DSCP map is a null map, which maps an incoming DSCP value to the same DSCP
value (no markdown).
Standard QoS Configuration Guidelines
Before beginning the QoS configuration, you should be aware of this information in these sections:
• “QoS ACL Guidelines” section on page 33-33
• “Applying QoS on Interfaces” section on page 33-33
• “Policing Guidelines” section on page 33-34
• “General QoS Guidelines” section on page 33-35
QoS ACL Guidelines
These are the guidelines with for configuring QoS with access control lists (ACLs):
• It is not possible to match IP fragments against configured IP extended ACLs to enforce QoS. IP
fragments are sent as best-effort. IP fragments are denoted by fields in the IP header.
• Only one ACL per class map and only one match class-map configuration command per class map
are supported. The ACL can have multiple ACEs, which match fields against the contents of the
packet.
• A trust statement in a policy map requires multiple TCAM entries per ACL line. If an input service
policy map contains a trust statement in an ACL, the access-list might be too large to fit into the
available QoS TCAM and an error can occur when you apply the policy map to a port. Whenever
possible, you should minimize the number of lines in a QoS ACL.
Applying QoS on Interfaces
These are the guidelines with for configuring QoS on physical ports. This section also applies to SVIs
(Layer 3 interfaces):
• You can configure QoS on physical ports and SVIs. When configuring QoS on physical ports, you
create and apply nonhierarchical policy maps. When configuring QoS on SVIs, you can create and
apply nonhierarchical and hierarchical policy maps.
• Incoming traffic is classified, policed, and marked down (if configured) regardless of whether the
traffic is bridged, routed, or sent to the CPU. It is possible for bridged frames to be dropped or to
have their DSCP and CoS values modified.
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