Service Manual

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 dierentiated actions for ECN/Non-ECN packets. After
classifying packets to ECN/Non-ECN, marking ECN and Non-ECN packets to dierent color packets is performed.
Policy based ingress QOS involves the following three steps to achieve QOS:
1. Classication of incoming trac.
2. Specify the dierentiated actions for dierent trac class.
3. Attach the policy-map to the interface.
Dell Networking OS support dierent types of match qualiers to classify the incoming trac.
Match qualiers can be directly congured in the class-map command or it can be specied through one or more ACL which in turn
species the combination of match qualiers.
Until Release 9.3(0.0), support is available for classifying trac based on the 6-bit DSCP eld of the IPv4 packet.
As a part of this feature, the 2-bit ECN eld of the IPv4 packet will also be available to be congured as one of the match qualier.
This way the entire 8-bit ToS eld of the IPv4 header shall be used to classify trac.
The Dell Networking OS Release 9.3(0.0) supports the following QOS actions in the ingress policy based QOS:
1. Rate Policing
2. Queuing
3. Marking
For the L3 Routed packets, the DSCP marking is the only marking action supported in the software. As a part of this feature, the
additional marking action to set the “color” of the trac will be provided.
Until Release 9.3(0.0), the software has the capability to qualify only on the 6-bit DSCP part of the ToS eld in IPv4 Header. You can
now accept and process incoming packets based on the 2-bit ECN part of the ToS eld in addition to the DSCP categorization. The
IPv4 ACLs (standard and Extended) are enhanced to add this qualier. This new keyword ‘ecn’ is present for all L3 ACL types
(TCP/UDP/IP/ICMP) at the level where the ‘DSCP’ qualier is positioned in the current ACL commands.
Dell Networking OS supports the capability to contain DSCP and ECN classiers simultaneously for the same ACL entry.
You can use the ecn keyword with the ip access-list standard, ip access-list extended, seq, and permit commands for standard and
extended IPv4 ACLs to match incoming packets with the specied ECN values.
Similar to ‘dscp’ qualier in the existing L3 ACL command, the ‘ecn’ qualier can be used along with all other supported ACL match
qualiers such as SIP/DIP/TCP/UDP/SRC PORT/DST PORT/ ICMP.
Until Release 9.3(0.0), ACL supports classication based on the below TCP ags:
• ACK
• FIN
• SYN
• PSH
• RST
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Quality of Service (QoS)