Concept Guide
– CIR < x< PIR – will be marked as “Yellow”
– PIR < x – will be marked as “Red”
But ‘Green’ packets matching the specic match criteria for which ‘color-marking’ is congured will be over-written and marked as “Yellow”.
Sample conguration to mark non-ecn packets as “yellow”
with Multiple trac class
Consider the example where there are no dierent trac classes that is all the packets are egressing on the default ‘queue0’.
Dell EMC Networking OS can be congured 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 Notication (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 congure 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 signicant 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 dierentiated actions for ECN/Non-ECN packets. After classifying
packets to ECN/Non-ECN, marking ECN and Non-ECN packets to dierent color packets is performed.
Policy based ingress QOS involves the following three steps to achieve QOS:
1 Classication of incoming trac.
2 Specify the dierentiated actions for dierent trac class.
3 Attach the policy-map to the interface.
Dell EMC Networking OS support dierent types of match qualiers to classify the incoming trac.
Match qualiers can be directly congured in the class-map command or it can be specied through one or more ACL which in turn
species the combination of match qualiers.
Until Release 9.3(0.0), support is available for classifying trac based on the 6-bit DSCP eld of the IPv4 packet.
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Quality of Service (QoS)