Concept Guide

CPU Processing of CoPP Traffic
The systems use FP rules to take the packets to control plane by CopyToCPU or redirect packet to CPU port. Only 8 CPU
queues are used while sending the packet to CPU. The CPU Management Interface Controller (CMIC) interface on all the
systems supports 48 queues in hardware. However, FTOS supports only 8 CMIC queues – 4 for data streams that are CPU
bound – SFLOW packets, packet streams that are trapped to CPU for logging info on MAC learn limit exceeded and other
violations, L3 packets with unknown destination for soft forwarding etc. Other 4 CMIC queues will carry the L2/L3 well-known
protocol streams. However there are about 20 well known protocol streams that have to share these 4 CMIC queues. Before
9.4.(0.0)Dell EMC Networking OS used only 8 queues most of the queues are shared to multiple protocols. So, increasing the
number of CMIC queues will reduce the contention among the protocols for the queue bandwidth.
Currently, there are 4 Queues for data and 4 for control in both front-end and back-plane ports. In stacked systems, the control
streams that reach standby or slave units will be tunneled through the backplane ports across stack-units to reach the CPU of
the master unit. In this case, the packets that reach slave unit’s CMIC via queues 0 – 7 will take same queues 0 – 7 on the
back-plane ports while traversing across units and finally on the master CMIC, they are queued on the same queues 0 – 7. In
this case, the queue (4 – 7) taken by the well-known protocol streams are uniform across different queuing points, and the
queue (0 – 3) taken by the CPU bound data streams are uniform. In back-plane ports, queue 0 – 3 will carry both the front-end
bound data streams as well as the CPU bound data streams which is acceptable but the well-known protocol streams must not
be mixed with the data streams on queues 0 – 3 in back-plane ports.
Increased CPU Queues for CoPP
FTOS classifies every packet ingress from the front end port to system as control traffic or data traffic by having the
pre-defined rules based on protocol type or packets types like ttl, slow path etc. FP is used to classify the traffic to transmit the
control traffic to CMIC port. Other major function performed by the FP rule is to decide to which CPU queue the packet must
be sent. All other packets will be forwarded or dropped at the ingress.
All packet transmitted to CPU will transmit to local CPU by using the CPU queues and processed. But in stacked system only
mater CPU is responsible for the control plane actions. So control packets received in master or slave units will be tunneled to
master CPU to process.
As part of enhancements, CPU queues are increased from 8 to 12 on CPU port. However, the front-end port and the backplane
ports support only 8 queues. As a result, when packets are transmitted to the local CPU, the CPU uses Q0-Q11 queues. The
control packets that are tunneled to the master unit are isolated from the data queues and the control queues in the backplane
links. Control traffic must be sent over the control queues Q4-Q7 on higig links. After reaching the master unit tunneled packets
must be transmitted to the CPU using the Q0-Q11 queues.
The backplane ports can have a maximum of 4 control queues. So, when we have more than ‘n’ CMIC queues for well-known
protocols and n > 4, then streams on ‘n’ CMIC queues must be multiplexed on 4 control queues on back-plane ports and on the
Master unit, these streams must be de-multiplexed to ‘n’ CMIC queues on the Master CPU.
After control packets reach the CPU through the CMIC port, the software schedules to process traffic on each 12 CPU queues.
This aspect must be ensured even in case of stand-alone systems and there is no dependency with stacking.
Policing provides a method for protecting CPU bound control plane packets by policing packets transmited to CPU with a
specified rate and from undesired or malicious traffic. This is done at each CPU queue on each unit.
FP Entries for Distribution of NDP Packets to Various CPU Queues
● At present generic mac based entries in system flow region will take IPv6 packets to CPU.
○ OSPFv3 – 33:33:0:0:0:5 – Q7
○ - 33:33:0:0:0:6 – Q7
○ IPv6 Multicast – 33:33:0:0:0:0 – Q1
● Add/remove specific ICMPv6 NDP protocol entry when user configures the first ipv6 address in the front panel port
○ Distribute ICMPv6 NS/RS packets to Q5.
○ Distribute ICMPv6 NA/RA packets to Q6.
FP is installed for all Front panel ports.
Control Plane Policing (CoPP)
235