Users Guide

CONFIGURATION mode
Dell(conf)#qos-policy-input pp_qospolicy
5. Congure the DSCP value to be set on matched packets.
QOS-POLICY-IN mode
Dell(conf-qos-policy-in)#set ip-dscp 5
6. Create an input policy map.
CONFIGURATION mode
Dell(conf)#policy-map-input pp_policmap
7. Create a service queue to associate the class map and QoS policy map.
POLICY-MAP mode
Dell(conf-policy-map-in)#service-queue 0 class-map pp_classmap qos-policy pp_qospolicy
Classifying Incoming Packets Using ECN and Color-Marking
Explicit Congestion Notication (ECN) is a capability that enhances WRED by marking the packets instead of causing WRED to drop
them when the threshold value is exceeded. If you congure ECN for WRED, devices employ this functionality of ECN to mark the
packets and reduce the rate of sending packets in a congested, heavily-loaded network.
ECN is a mechanism using which network switches indicate congestion to end hosts for initiating appropriate action. End hosts uses
two least signicant bits of ToS to indicate that it is ECT. When intermediate network node encounters congestion, remarks ECT to
CE for end host to take appropriate action. During congestion, ECN enabled packets are not subject to any kind of drops like WRED
except tail drops. Though ECN & WRED are independent technologies, BRCM has made WRED a mandatory for ECN to work.
On ECN deployment, the non-ECN packets that are transmitted on the ECN-WRED enabled interface will be considered as Green
packets and will be subject to the early WRED drops. Typically the TCP-acks, OAM, ICMP ping packets will be non-ECN in nature
and it is not desirable for this packets getting WRED dropped.
In such a condition, it is necessary that the switch is capable to take dierentiated actions for ECN/Non-ECN packets. After
classifying packets to ECN/Non-ECN, marking ECN and Non-ECN packets to dierent color packets is performed.
Policy based ingress QOS involves the following three steps to achieve QOS:
1. Classication of incoming trac.
2. Specify the dierentiated actions for dierent trac class.
3. Attach the policy-map to the interface.
Dell Networking OS support dierent types of match qualiers to classify the incoming trac.
Match qualiers can be directly congured in the class-map command or it can be specied through one or more ACL which in turn
species the combination of match qualiers.
Until Release 9.3(0.0), support is available for classifying trac based on the 6-bit DSCP eld of the IPv4 packet.
As a part of this feature, the 2-bit ECN eld of the IPv4 packet will also be available to be congured as one of the match qualier.
This way the entire 8-bit ToS eld of the IPv4 header shall be used to classify trac.
The Dell Networking OS Release 9.3(0.0) supports the following QOS actions in the ingress policy based QOS:
1. Rate Policing
2. Queuing
3. Marking
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Quality of Service (QoS)