When monitoring high-speed network interfaces via SNMP, many engineers encounter puzzling differences between the classic 32-bit counters (ifInOctets/ifOutOctets) and their high-capacity 64-bit counterparts (ifHCInOctets/ifHCOutOctets). The values don't always show the same traffic deltas, which raises questions about data reliability.

Consider these actual SNMP walk outputs from a router interface:

First sample:
IF-MIB::ifInOctets.2 = Counter32: 2291487255
IF-MIB::ifHCInOctets.2 = Counter64: 2901400127083

Second sample (10s later):
IF-MIB::ifInOctets.2 = Counter32: 2297202283
IF-MIB::ifHCInOctets.2 = Counter64: 2901400298056

The deltas show:

• 32-bit counter change: 5,715,028 octets
• 64-bit counter change: 170,973 octets

Several technical factors explain these discrepancies:

1. Update Frequency: Some devices update 32-bit counters more frequently than 64-bit counters
2. Sampling Artifacts: The counters might be sampled at slightly different times
3. Hardware Acceleration: Certain traffic might bypass software counters but still hit hardware counters
4. Driver Implementation: Different kernel network drivers might handle the counters differently

For accurate traffic measurement:

# Always prefer HC counters for high-speed interfaces (> 1Gbps)
snmpwalk -v2c -c public router IF-MIB::ifHCInOctets

# For legacy systems, implement overflow detection:
if (new_32bit_value < previous_32bit_value) {
    delta = (MAX_32BIT - previous_32bit_value) + new_32bit_value;
} else {
    delta = new_32bit_value - previous_32bit_value;
}

Here's a Python snippet that handles both counter types:

from pysnmp.hlapi import *

def get_interface_stats(host, if_index):
    errorIndication, errorStatus, errorIndex, varBinds = next(
        getCmd(SnmpEngine(),
               CommunityData('public'),
               UdpTransportTarget((host, 161)),
               ContextData(),
               ObjectType(ObjectIdentity('IF-MIB', 'ifHCInOctets', if_index)),
               ObjectType(ObjectIdentity('IF-MIB', 'ifInOctets', if_index)))
    )
    
    if errorIndication:
        print(errorIndication)
    elif errorStatus:
        print(f"{errorStatus.prettyPrint()} at {errorIndex and varBinds[int(errorIndex)-1][0] or '?'}")
    else:
        hc_value = int(varBinds[0][1])
        std_value = int(varBinds[1][1])
        return (hc_value, std_value)

While the 32-bit counters match /proc/net/dev, the 64-bit HC counters provide more reliable data for high-speed interfaces despite occasional discrepancies. Implement proper counter wrapping detection and prefer HC counters where available.

When monitoring high-speed network interfaces through SNMP, network engineers often encounter inconsistencies between the traditional 32-bit counters (ifInOctets/ifOutOctets) and their 64-bit counterparts (ifHCInOctets/ifHCOutOctets). As shown in the example data:

IF-MIB::ifInOctets.2 = Counter32: 2291487255
IF-MIB::ifHCInOctets.2 = Counter64: 2901400127083

We observe that the deltas between polling intervals don't always match, sometimes showing significant percentage differences in either direction.

The fundamental difference lies in their implementation:

• ifInOctets (32-bit): Standard counter that wraps after 4,294,967,295 octets (RFC 2863)
• ifHCInOctets (64-bit): High-capacity counter that won't wrap in practical scenarios (RFC 2863)

Several factors contribute to the observed differences:

# Example showing inconsistent deltas
Poll 1: 
  32-bit: 2291487255
  64-bit: 2901400127083

Poll 2:
  32-bit: 2297202283 (+5,715,028)
  64-bit: 2901400298056 (+170,973)

1. Sampling Timing: The counters may be updated at slightly different intervals in the device's kernel

2. Hardware vs Software Counters: Some implementations use different data sources

3. Counter Resets: The 32-bit counter may have wrapped between polls

4. Driver Implementation: Vendor-specific behaviors in counter updates

For reliable network traffic monitoring, consider these approaches:

# Python example for proper counter handling
import pysnmp.hlapi as snmp

def get_64bit_counter(host, community, oid):
    errorIndication, errorStatus, errorIndex, varBinds = next(
        snmp.getCmd(snmp.SnmpEngine(),
                   snmp.CommunityData(community),
                   snmp.UdpTransportTarget((host, 161)),
                   snmp.ContextData(),
                   snmp.ObjectType(snmp.ObjectIdentity(oid)))
    )
    if errorIndication:
        print(errorIndication)
    elif errorStatus:
        print(f"{errorStatus.prettyPrint()} at {errorIndex}")
    else:
        return int(varBinds[0][1])

Best Practice Recommendations:

• Always prefer 64-bit counters (ifHC*) for interfaces faster than 100Mbps
• Implement proper counter wrap detection in your monitoring code
• Use consistent polling intervals (recommended: 30-300 seconds)
• Verify counter behavior with your specific network equipment

When dealing with legacy devices that only support 32-bit counters:

# Bash script to handle counter wraps
prev_value=0
current_value=$(snmpget -v2c -c public router ifInOctets.2 | awk '{print $4}')

if (( current_value < prev_value )); then
    delta=$((4294967295 - prev_value + current_value))
else
    delta=$((current_value - prev_value))
fi

For the most accurate results, combine data from both counter types where available and implement validation checks in your monitoring solution.