Service Manual

Guidelines for Conguring ECN for Classifying and Color-Marking
Packets
Keep the following points in mind while conguring the marking and mapping of incoming packets using ECN elds in IPv4 headers:
• Currently Dell Networking OS supports matching only the following TCP ags:
– ACK
– FIN
– SYN
– PSH
– RST
– URG
In the existing software, ECE/CWR TCP ag qualiers are not supported.
• Because this functionality forcibly marks all the packets matching the specic match criteria as ‘yellow’, Dell 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 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
Quality of Service (QoS)
607