Dell PowerSwitch S4820T Configuration Guide for the S4820T System 9.100.0 - Page 225

CoPP for OSPFv3 Packets You can create an IPv6 ACL for control-plane traffic policing for OSPFv3, in addition to the CoPP support for VRRP, BGP, and ICMP. You can use the ipv6 access-list name cpu-qos permit ospfv3 command to allow CoPP traffic for OSPFv3. Control Plane Policing (CoPP) enables more number of CPU queues to be made available on ports for IPv6 and ICMPv6 packets. 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 wellknown 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. Control Plane Policing (CoPP) 225