Cisco Systems IE 2000 Standard QoS Configuration Guidelines

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Cisco IE 2000 Switch Software Configuration Guide
OL-25866-01
Chapter 38 Configuring Standard QoS
Information About Standard QoS
Figure 38-2 Standard QoS Model
Standard QoS Configuration Guidelines
QoS ACL
These are the guidelines for configuring QoS with access control lists (ACLs):
• 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.
QoS on Interfaces
These are the guidelines for configuring QoS on physical ports. This section also applies to SVIs (La yer
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 br idged frames to be dropped or to
have their DSCP and CoS values modified.
• Follow these guidelines when configuring policy maps on physical ports or SVIs:
– You cannot apply the same policy map to a physical port and to an SVI.
– If VLAN-based QoS is configured on a physical port, the switch removes all t he port-based
policy maps on the port. The traffic on this physical port is now affecte d by the policy map
attached to the SVI to which the physical port belongs.