Software Qos - Cisco Catalyst 4500 series Administration Manual

Configuring QoS on a Standalone Supervisor Engine 6-E/6L-E or Supervisor Engine 7-E/7L-E/8-E
Qos Policy merging
Applicable policies are applied to a given packet in given direction. For example, if you configure egress
VLAN-based police and marking, followed by selective queuing on the port, then actions from both
policies will be applied for this packet.
The following policy-map configuration restrictions are imposed on an EtherChannel:
•
•
A packet can be marked (dscp or cos fields) by the EtherChannel policy. If the physical member port
policy uses a classification based on dscp or cos fields, it must be based on the marked (modified) value.
To ensure proper operation, the following restriction is placed on the EtherChannel.
The classification criteria for the policy-map on the physical member ports has to based only on one type
of field:
•
•
•
•
Classification criteria for the policy-map on the physical member ports cannot be based on a combination
of fields. This restriction ensures that if the EtherChannel policy is marking down dscp or cos, the
marked (modified) value-based classification can be implemented in hardware.
Classification criteria for the policy-map on the physical member ports cannot be modified to add a new
Note
type of field.
Auto-QoS is not supported on EtherChannel or its member ports. A physical port configured with
Auto-QoS is not allowed to become a member of a physical port.

Software QoS

At the highest level, there are two types of locally sourced traffic (such as control protocol packets,
pings, and telnets) from the switch: high priority traffic (typically the control protocol packets like OSPF
Hellos and STP) and low priority packets (all other packet types).
The QoS treatment for locally-sourced packets differs for the two types.
The supervisor engine provides a way to apply QoS to packets processed in the software path. The
packets that get this QoS treatment in software can be classified into two types: software switched
packets and software generated packets.
On reception, software switched packets are sent to the CPU that in turn sends them out of another
interface. For such packets, input software QoS provides input marking and output software QoS
provides output marking and queue selection.
The software generated packets are the ones locally sourced by the switch. The type of output software
QoS processing applied to these packets is the same as the one applied to software switched packets. The
only difference in the two is that the software switched packets take input marking of the packet into
account for output classification purpose.
Software Configuration Guide—Release IOS XE 3.6.0E and IOS 15.2(2)E
42-74
only policing and marking actions are supported at the EtherChannel level
only queuing actions are supported at the physical member port level
dscp
precedence
cos
any non marking field (no dscp or cos based classification)
Chapter 42 Configuring Quality of Service
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