Dell Force10 Z9000 Configuration Manual page 215

Prior to the release 9.4.(0.0), all IPv6 packets are taken to same queues there is no priority between the ICMPv6 packets and
unknown IPv6 packets. Due to this NS/NA/RS/RA packets not given high priority leads to the session establishment problem. To
solve this issue, starting from release 9.4.(0.0), IPv6 NDP packets use different CPU queues when compared to the Generic IPv6
multicast traffic. These entries are installed in system when application is triggered..
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 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
Control Plane Policing (CoPP)
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