Classification Based On Dei; Ip Precedence Compared To Ip Dscp Marking; In-Place Policy Modification - Cisco ASR 9000 Series Service Configuration Manual

Configuring Modular QoS Service Packet Classification and Marking on Cisco ASR 9000 Series Routers

Classification Based on DEI

You can classify traffic based on the Drop Eligible Indicator (DEI ) bit that is present in 802.1ad frames
and in 802.1ah frames. Default DEI marking is supported. The set DEI action in policy maps is supported
on 802.1ad packets for:
•
•
•
•
The set DEI action is ignored for traffic on interfaces that are not configured for 802.1ad encapsulation.
Note
Default DEI Marking
Incoming Packet
802.1q packet
802.1ad packet
802.1q packet translated to
802.1ad packet
or
802.1ad packet

IP Precedence Compared to IP DSCP Marking

The IP DSCP value is the first six bits in the ToS byte, and the IP precedence value is the first three bits
in the ToS byte. The IP precedence value is actually part of the IP DSCP value. Therefore, both values
cannot be set simultaneously.
If you need to mark packets in your network and all your devices support IP DSCP marking, use the IP
DSCP marking to mark your packets because the IP DSCP markings provide more unconditional packet
marking options. If marking by IP DSCP is undesirable, however, or if you are unsure if the devices in
your network support IP DSCP values, use the IP precedence value to mark your packets. The IP
precedence value is likely to be supported by all devices in the network.
You can set up to 8 different IP precedence markings and 64 different IP DSCP markings.

In-Place Policy Modification

The In-Place Policy Modification feature allows you to modify a QoS policy even when the QoS policy
is attached to one or more interfaces. When you modify the QoS policy attached to one or more
interfaces, the QoS policy is automatically modified on all the interfaces to which the QoS policy is
attached. A modified policy is subject to the same checks that a new policy is subject to when it is bound
to an interface.
OL-23108-02
Information About Configuring Modular QoS Packet Classification and Marking on Cisco ASR 9000 Series Routers
Ingress and egress
Layer 2 subinterfaces
Layer 2 main interfaces
Layer 3 main interfaces
Cisco ASR 9000 Series Aggregation Services Router Modular Quality of Service Configuration Guide
Ingress Set Action
None
None
set dei {0 | 1}
Default DEI on Imposed 802.1ad Headers
0
DEI of top-most tag of the incoming
packet
0 or 1
Based on DEI value in the set action
QC-17