Dell N3200-ON EMC Networking N-Series Switches CLI Reference Guide version 6.7 - Page 1181

When the ARP or neighbor table is filled, the switch cannot accommodate new entries. In this case, there is no value in receiving the unresolved IPv4/IPv6 packets. Likewise, in cases of a L2 network re-convergence, a large number of neighbors may not be discovered but may be transmitting traffic. In the case of multicast data, certain multicast topologies using multi-access VLANs may result in packets being forwarded to the CPU with no associated PIM or MFDB state. Receiving large numbers unresolved packets spikes the CPU usage to high levels at no benefit. For Ipv6, it also results in delayed processing of the NUD packets (NS/NA) for the existing neighbor entries leading to NUD anomalies and deletions of existing neighbor entries. To avoid such an unnecessary CPU load leading to NUD anomalies when the ARP or IPV6 neighbor table is close to full (crossing 95% of table size) or other failures, the switch automatically reduces the rate limit to an empirical value of 50 pps irrespective of the configured rate limit. When the table size falls below 95% of the table size, it is restored to the configured rate limit value. Use this command to limit the CPU load in situations where large numbers of unknown multicast or IPv4/IPv6 packets with an unknown multicast or unicast IPv4/IPv6 destination are being handled in software. The symptom can be diagnosed by high CPU usage of the ipMapForwardingTask. Example An example output is showing higher than normal CPU usage due to packets copied to the software forwarding task below: console#show process cpu Memory Utilization Report status bytes free 1055653888 alloc 672153600 CPU Utilization: PID Name 5 Secs 60 Secs 300 Secs 1129 osapiTimer 0.09% 0.02% 0.01% Security Commands 1181