Cisco Systems 2960-S, 2960 Standard QoS Configuration Guidelines

33-38
Catalyst 2960 and 2960-S Switch Software Configuration Guide
OL-8603-09
Chapter 33 Configuring QoS
Configuring Standard QoS
Table 33-11 shows the default DSCP output queue threshold map when QoS is enabled.
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 33-38
• “Policing Guidelines” section on page 33-39
• “General QoS Guidelines” section on page 33-39
QoS ACL Guidelines
• If you use QoS ACLs for classification, you can use the sdm prefer qos global configuration
command to set the Switch Database Management (SDM) feature to the QoS template. SDM
configures system resources to support the maximum number of access contro l entries (ACEs). For
more information on the SDM templates, see Chapter 8, “Configuring SDM Templates.”
• It is not possible to match IP fragments against configured IP extended ACLs to enforce Qo S. 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.
Table 33-11 Default DSCP Output Queue Threshold Map
DSCP Value Queue ID–Threshold ID
0–15 2–1
16–31 3–1
32–39 4–1
40–47 1–1
48–63 4–1