Dell S4048T Configuration Manual page 287

CoPP enhancements are to enhance the capability of FTOS by utilizing more number of CPU queues on
CMIC port and sending control packets to different queues that internally reduce limitation or contention of
control protocols sharing the same queues (that is, before this functionality of CoPP for OSPV3 was
introduced, OSPF might have caused the LACP flap because of both control traffic sent to same Q7 on CPU
port). Non CPU port should have only 4 dedicated control queues and remaining shared for both data and
traffic. Number of control queues is increased on the CPU port. When tunneling packets from non-master to
master unit, high-gig queues are used.
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.
Control Plane Policing (CoPP) 287