Guidelines For Configuring Ecn For Classifying And Color-Marking Packets; Sample Configuration To Mark Non-Ecn Packets As "Yellow" With Multiple Traffic Class; Classifying Incoming Packets Using Ecn And Color-Marking - Dell Force10 Z9000 Configuration Manual

Guidelines for Configuring ECN for Classifying and Color-Marking
Packets
Keep the following points in mind while configuring the marking and mapping of incoming packets using ECN fields in IPv4 headers:
• Currently Dell Networking OS supports matching only the following TCP flags:
– ACK
– FIN
– SYN
– PSH
– RST
– URG
In 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 less than PIR would be considered
as "Green" But 'Green' packets matching the specific match criteria for which '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 be over-written and marked as
"Yellow".

Sample configuration to mark non-ecn packets as "yellow" with Multiple traffic class

Consider the example where there are no different traffic classes that is all the packets are egressing on the default 'queue0'.
Dell Networking OS can be configured 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
!
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 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
598
Quality of Service (QoS)
yellow