SNMP Data Collection Reference

This page provides reference information for SNMP data collection in NetXMS.

For practical instructions on creating SNMP DCIs, see SNMP Data Collection. For an explanation of SNMP table OID structure, see Understanding SNMP Table Structure.

OID Format

OIDs in DCI configuration must be numeric, in dotted decimal notation (e.g., .1.3.6.1.2.1.1.3.0). Symbolic forms such as SNMPv2-MIB::sysUpTime.0 are not accepted. When you select an OID in the MIB browser, the numeric OID is inserted automatically.

Counter Handling

SNMP counters (Counter32, Counter64) are monotonically increasing values. To convert them into a rate, set the DCI delta calculation to Average delta per second or Average delta per minute — the data type by itself does not compute rates. Setting the data type to Counter 32-bit or Counter 64-bit additionally enables counter wrap/reset handling within delta calculation.

For 32-bit counters on fast interfaces, counter wraps may occur between polls. Use 64-bit counters (ifHCInOctets/ifHCOutOctets) on fast interfaces when the device supports them.

Performance Considerations

  • NetXMS walks SNMP tables using GetNext requests (GetBulk is not used); table rows are then read with multi-varbind GET requests. If the device responds with a tooBig error, the server silently falls back to reading one column per GET request

  • Large SNMP walks can take considerable time on devices with many OIDs; consider narrowing the walk scope

  • Avoid polling the same device too frequently to keep the load on the device’s SNMP agent reasonable

  • Use SNMP proxy when polling devices that are not directly reachable from the server or that belong to a separate zone (see SNMP Proxy)

Troubleshooting

SNMP Timeout

  • Verify the device is reachable and SNMP is enabled

  • Check community string or v3 credentials (see SNMP Configuration)

  • Verify firewall rules allow UDP port 161

  • Try increasing the SNMP.RequestTimeout (default: 1500 ms) or SNMP.RetryCount (default: 3) server configuration variables; changes to either take effect after server restart

OID Returns Wrong Type

  • Check the MIB definition for the correct data type (see MIB Management)

  • Some devices return string representations of numbers — set the DCI data type accordingly

  • For counters, set the DCI data type to Counter 32-bit or Counter 64-bit so counter wraps are handled during delta calculation

Missing OIDs After Walk

  • The device may not implement all OIDs defined in the MIB

  • Try walking a broader subtree

  • Check if the device requires specific community string or context for access to certain OID trees