Concept Guide

• Because this functionality forcibly marks all the packets matching the specic match criteria as ‘yellow’, Dell EMC Networking OS does
not support Policer based coloring and this feature concurrently.
• If single rate two color policer is congured along with this feature, then by default all packets less than PIR would be considered as
“Green” But ‘Green’ packets matching the specic match criteria for which ‘color-marking’ is congured will be over-written and
marked as “Yellow”.
• If two rate three color policer is congured along with this feature then,
– x < CIR – will be marked as “Green”
– CIR < x< PIR – will be marked as “Yellow”
– PIR < x – will be marked as “Red”
But ‘Green’ packets matching the specic match criteria for which ‘color-marking’ is congured will be over-written and marked as “Yellow”.
Sample conguration to mark non-ecn packets as “yellow”
with Multiple trac class
Consider the example where there are no dierent trac classes that is all the packets are egressing on the default ‘queue0’.
Dell EMC Networking OS can be congured as below to mark the non-ecn packets as yellow packets.
!
ip access-list standard ecn_0
seq 5 permit any ecn 0
class-map match-any ecn_0_cmap
match ip access-group ecn_0 set-color yellow
!
policy-map-input ecn_0_pmap
service-queue 0 class-map ecn_0_cmap
Applying this policy-map “ecn_0_pmap” will mark all the packets with ‘ecn == 0’ as yellow packets on queue0 (default queue).
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.
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Quality of Service (QoS)