Dell S4048T, Руководство по настройке

Страница: 860 / 1277

• 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 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 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.
Quality of Service (QoS) 860