Users Guide

Dell(conf-class-map)#match ipdscp 5
3 Configure an IP VLAN ID as a match criterion.
CLASS-MAP mode
Dell(conf-class-map)#match ip vlan 5
4 Create a QoS input policy.
CONFIGURATION mode
Dell(conf)#qos-policy-input pp_qospolicy
5 Configure 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 Notification (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 configure 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 significant 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 differentiated actions for ECN/Non-ECN
packets. After classifying packets to ECN/Non-ECN, marking ECN and Non-ECN packets to different color
packets is performed.
Policy based ingress QOS involves the following three steps to achieve QOS:
1 Classification of incoming traffic.
Quality of Service (QoS) 779