Cisco Catalyst 4500 Series, Руководство по настройке программного обеспечения, Страница: 1136 / 2086

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Catalyst 4500 Series Switch, Cisco IOS Software Configuration Guide - Cisco IOS XE 3.9.xE and IOS 15.2(5)Ex
Chapter 44 Configuring Quality of Service
Configuring VSS QoS
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:
•
only policing and marking actions are supported at the EtherChannel level
• only queuing actions are supported at the physical member port level
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:
•
dscp
•
precedence
•
cos
• any non marking field (no dscp or cos based classification)
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.
Note
Auto-QoS macros with SRND4 generate class-maps with more than one type of match. These
class-maps need to be modified to use only with one matching type when applied on EtherChannel
member ports.
Note Classification criteria for the policy-map on the physical member ports cannot be modified to add a new
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.