– SYN– PSH– RST– URGIn the existing software, ECE/CWR TCP flag qualifiers are not supported.• Because this functionality forcibly marks all the packets matching the specific match criteria as‘yellow’, Dell Networking OS does not support Policer based coloring and this feature concurrently.• If single rate two color policer is configured along with this feature, then by default all packets lessthan PIR would be considered as “Green” But ‘Green’ packets matching the specific match criteria forwhich ‘color-marking’ is configured will be over-written and marked as “Yellow”.• If two rate three color policer is configured 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 specific match criteria for which ‘color-marking’ is configured will beover-written and marked as “Yellow”.Sample configuration to mark non-ecn packets as “yellow” with Multipletraffic classConsider the example where there are no different traffic classes that is all the packets are egressing onthe default ‘queue0’.Dell Networking OS can be configured as below to mark the non-ecn packets as yellow packets.!ip access-list standard ecn_0seq 5 permit any ecn 0class-map match-any ecn_0_cmapmatch ip access-group ecn_0 set-color yellow!policy-map-input ecn_0_pmapservice-queue 0 class-map ecn_0_cmapApplying this policy-map “ecn_0_pmap” will mark all the packets with ‘ecn == 0’ as yellow packets onqueue0 (default queue).Classifying Incoming Packets Using ECN and Color-MarkingExplicit Congestion Notification (ECN) is a capability that enhances WRED by marking the packets insteadof 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 acongested, heavily-loaded network.ECN is a mechanism using which network switches indicate congestion to end hosts for initiatingappropriate action. End hosts uses two least significant bits of ToS to indicate that it is ECT. Whenintermediate network node encounters congestion, remarks ECT to CE for end host to take appropriateaction. During congestion, ECN enabled packets are not subject to any kind of drops like WRED exceptQuality of Service (QoS) 677
