Dell S4048T Configuration Manual page 288

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.
NDP Packets
Neighbor discovery protocol has 4 types of packets NS, NA, RA, RS. These packets need to be taken to CPU
for neighbor discovery.
• Unicast NDP packets:
• Packets hitting the L3 host/route table and discovered as local terminated packets/CPU bound
traffic. For CPU bound traffic route entry have CPU action. Below are packets are CPU bound
traffic.
• Packets destined to chassis.
• Route with Unresolved Arp
Control Plane Policing (CoPP) 288