SNMP#NET添加OID查询Windows CPU温度报错及额外OID添加咨询

Let's break down your problem step by step:

Why does the OID 1.3.6.1.2.1.25.3.3.1.2 throw an error? #

The OID 1.3.6.1.2.1.25.3.3.1.2 maps to hrProcessorLoad in the HOST-RESOURCES-MIB, which is a table-based object (it represents a collection of values, one for each CPU core/processor on the system).

Your original code uses a SNMPv1 Get request (PduType.Get), which is only designed to fetch scalar OIDs (those ending with .0, like the system info OIDs you used initially). When you try to query a table OID with a Get request, the SNMP agent (or SNMP#NET's parsing logic) throws SnmpInvalidPduTypeException because this combination is invalid for SNMPv1.

For table objects, you need to use either:

• GetNext requests (to iterate through table entries one by one)
• GetBulk requests (available in SNMPv2c/v3, which fetches multiple table entries at once)

How to correctly add OIDs in SNMP#NET requests #

1. Adding scalar OIDs (like your original system info ones) #

This is straightforward—just keep using the PduType.Get request and add the scalar OIDs (ending with .0) to the VbList as you did before:

Pdu pdu = new Pdu(PduType.Get);
// Add existing system info scalars
pdu.VbList.Add("1.3.6.1.2.1.1.1.0"); // sysDescr
pdu.VbList.Add("1.3.6.1.2.1.1.2.0"); // sysObjectID
// Add another scalar OID example
pdu.VbList.Add("1.3.6.1.2.1.25.1.1.0"); // hrSystemUptime

2. Querying table OIDs (like hrProcessorLoad) #

Since you're using SNMPv1, you'll need to use GetNext requests to retrieve table entries. Here's a modified example for fetching CPU load values:

OctetString community = new OctetString("public");
AgentParameters param = new AgentParameters(community);
IpAddress agent = new SnmpSharpNet.IpAddress(ipaddress);
UdpTarget target = new UdpTarget((IPAddress)agent, 161, 2000, 1);

// Use GetNext for table OIDs
Pdu pdu = new Pdu(PduType.GetNext);
// Add the base table OID (without the index suffix)
pdu.VbList.Add("1.3.6.1.2.1.25.3.3.1.2");

SnmpV1Packet result = (SnmpV1Packet)target.Request(pdu, param);

if (result != null && result.Pdu.ErrorStatus == 0)
{
    foreach (Vb vb in result.Pdu.VbList)
    {
        Console.WriteLine($"CPU Load OID: {vb.Oid.ToString()} | Value: {vb.Value.ToString()}");
        // To get more entries, you'd send another GetNext with the last returned OID
    }
}
else
{
    Console.WriteLine($"Error: {result?.Pdu.ErrorStatus.ToString() ?? "No response"}");
}

target.Close();

If you can switch to SNMPv2c, GetBulk is more efficient for fetching multiple table entries at once:

// Switch to SNMPv2c parameters
AgentParameters param = new AgentParameters(community);
param.Version = SnmpVersion.Ver2;

Pdu pdu = new Pdu(PduType.GetBulk);
pdu.NonRepeaters = 0;
pdu.MaxRepetitions = 10; // Number of entries to fetch
pdu.VbList.Add("1.3.6.1.2.1.25.3.3.1.2");

SnmpV2Packet result = (SnmpV2Packet)target.Request(pdu, param);

if (result != null && result.Pdu.ErrorStatus == 0)
{
    foreach (Vb vb in result.Pdu.VbList)
    {
        Console.WriteLine($"CPU Load OID: {vb.Oid.ToString()} | Value: {vb.Value.ToString()}");
    }
}

Key Notes: #

• Always check if the OID you're querying is a scalar (ends with .0) or part of a table. You can confirm this using MIB browsers or OID lookup tools.
• For SNMPv1, table queries require iterative GetNext requests. SNMPv2c/v3's GetBulk simplifies this by fetching multiple entries in one go.
• Make sure the target Windows machine has SNMP enabled and the community string matches, and that the HOST-RESOURCES-MIB is supported (most modern Windows SNMP agents do support it).

内容的提问来源于stack exchange，提问作者B Minster