Symptom

When polling cumulative interface counters over SNMP, in some cases the switch may incorrectly return a zero value. This only happens if there is an FX3 Nexus switch in FEX mode attached to this switch, and the interface returning the zero value doesn't need to be related to the FEX. If an NMS uses the difference between two subsequent poll results to calculate interface throughput, this bug may cause the NMS to erroneously display a spike in traffic. Example: snmpwalk -v 2c -c cisco123 10.122.176.117 iso.3.6.1.2.1.31.1.1.1.10.436233216 IF-MIB::ifHCOutOctets.436233216 = Counter64: 1396280 IF-MIB::ifHCOutOctets.436233216 = Counter64: 1396280 IF-MIB::ifHCOutOctets.436233216 = Counter64: 1396280 IF-MIB::ifHCOutOctets.436233216 = Counter64: 1396280 IF-MIB::ifHCOutOctets.436233216 = Counter64: 0 IF-MIB::ifHCOutOctets.436233216 = Counter64: 0 IF-MIB::ifHCOutOctets.436233216 = Counter64: 0 IF-MIB::ifHCOutOctets.436233216 = Counter64: 0 IF-MIB::ifHCOutOctets.436233216 = Counter64: 1414357 IF-MIB::ifHCOutOctets.436233216 = Counter64: 1414357 IF-MIB::ifHCOutOctets.436233216 = Counter64: 1414357 IF-MIB::ifHCOutOctets.436233216 = Counter64: 1414357 IF-MIB::ifHCOutOctets.436233216 = Counter64: 1414357 IF-MIB::ifHCOutOctets.436233216 = Counter64: 0 IF-MIB::ifHCOutOctets.436233216 = Counter64: 0 IF-MIB::ifHCOutOctets.436233216 = Counter64: 0 IF-MIB::ifHCOutOctets.436233216 = Counter64: 0 IF-MIB::ifHCOutOctets.436233216 = Counter64: 1436954 IF-MIB::ifHCOutOctets.436233216 = Counter64: 1436954 IF-MIB::ifHCOutOctets.436233216 = Counter64: 1436954

Conditions

Nexus 9K running 9.3.11 version with N9K FX3 (FEX) as FEX, then SNMP polling for interface utilisation randomly returns zero values.

Workaround

Fix is available from 10.2.x releases

Further Problem Description