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SNMP v1 and v2c were designed to be simple, but one significant issue of them is security. It is very hard to hide community strings from sniffers, and also difficult to set access control on entities.

IETF recognized SNMP v3 RFC documents in 2004, which uses a new design to address the security concerns. The changes were so huge, so #SNMP has to expose a different styles of APIs for developers to perform v3 operations.

Below a few SNMP v3 operations (GET, SET and so on) are translated to #SNMP function calls,

Discovery Process

SNMP v3 defines a discovery process in RFC 3414, that before an SNMP agent responds to a manager the two must interchange information such as time stamp, engine ID and so on.

Discovery discovery = Messenger.GetNextDiscovery(SnmpType.GetRequestPdu);
ReportMessage report = discovery.GetResponse(60000, new IPEndPoint(IPAddress.Parse("192.168.1.2"), 161));

Above we perform such a discovery process by sending out a GetRequestPdu type of discovery message, and the agent replies with a ReportMessage which we can reuse later to construct a valid request.

User Credentials

SNMP v3 requires user credentials to be passed on in each requests, so we need to prepare that information ahead of time.

var auth = new SHA1AuthenticationProvider(new OctetString("myauthenticationpassword"));
var priv = new DESPrivacyProvider(new OctetString("myprivacypassword"), auth);

Assume the agent requires both authentication (SHA-1) and privacy (DES) protection, then above we create a single provider that embeds both passwords.

GET Operation

The following code shows how to send an SNMP v3 GET message to an agent located 192.168.1.2 and query on OID 1.3.6.1.2.1.1.1.0,

GetRequestMessage request = new GetRequestMessage(VersionCode.V3, Messenger.NextMessageId, Messenger.NextRequestId, new OctetString("myname"), new List<variable>{new Variable(new ObjectIdentifier("1.3.6.1.2.1.1.1.0"))}, priv, Messenger.MaxMessageSize, report);
ISnmpMessage reply = request.GetResponse(60000, new IPEndPoint(IPAddress.Parse("192.168.1.2"), 161));
if (reply.Pdu().ErrorStatus.ToInt32() != 0) // != ErrorCode.NoError
{
    throw ErrorException.Create(
        "error in response",
        IPAddress.Parse("192.168.1.2"),
        reply);
}

The reply object usually contains the response message we expect. By accessing reply.Pdu().Variables we can see what data are returned.

SET Operation

The following code shows how to send an SNMP v3 SET message to an SNMP agent located at 192.168.1.2 and set the value of OID 1.3.6.1.2.1.1.6.0 to "Shanghai",

SetRequestMessage request = new GetRequestMessage(VersionCode.V3, Messenger.NextMessageId, Messenger.NextRequestId, new OctetString("myname"), new List<variable>{new Variable(new ObjectIdentifier("1.3.6.1.2.1.1.1.0"), new OctetString("Shanghai"))}, priv, Messenger.MaxMessageSize, report);
ISnmpMessage reply = request.GetResponse(60000, new IPEndPoint(IPAddress.Parse("192.168.1.2"), 161));
if (reply.Pdu().ErrorStatus.ToInt32() != 0) // != ErrorCode.NoError
{
    throw ErrorException.Create(
        "error in response",
        IPAddress.Parse("192.168.1.2"),
        reply);
}

GET-BULK Operation

The following code shows how to send an SNMP v3 GET-BULK message to an SNMP agent located at 192.168.1.2 and query on OID 1.3.6.1.2.1.1.1.0,

GetBulkRequestMessage request = new GetBulkRequestMessage(VersionCode.V3, Messenger.NextMessageId, Messenger.NextRequestId, new OctetString("myname"), 0, 10, new List<variable>{new Variable(new ObjectIdentifier("1.3.6.1.2.1.1.1.0"))}, priv, Messenger.MaxMessageSize, report);
ISnmpMessage reply = request.GetResponse(60000, new IPEndPoint(IPAddress.Parse("192.168.1.2"), 161));
if (reply.Pdu().ErrorStatus.ToInt32() != 0) // != ErrorCode.NoError
{
    throw ErrorException.Create(
        "error in response",
        IPAddress.Parse("192.168.1.2"),
        reply);
}

var result = reply.Pdu().Variables;

WALK Operation

The following code shows how to perform v3 WALK on an SNMP agent located at 192.168.1.2 starting at 1.3.6.1.2.1.1,

var result = new List<variable>();
Messenger.BulkWalk(VersionCode.V3, 
                   new IPEndPoint(IPAddress.Parse("192.168.1.2"), 161), 
                   new OctetString("public"), 
                   new ObjectIdentifier("1.3.6.1.2.1.1"), 
                   result, 
                   60000, 
                   10, 
                   WalkMode.WithinSubtree, 
                   priv, 
                   report);

TRAP v2 Operation

Note that TRAP v1 message format is obsolete by TRAP v2. Thus, for SNMP v3 TRAP operations, you can only use TRAP v2 message format.

The following code shows how to send a TRAP v2 message to an SNMP manager/trap listener located at 192.168.1.2,

var trap = new TrapV2Message(
                VersionCode.V3,
                528732060,
                1905687779,
                new OctetString("neither"),
                new ObjectIdentifier("1.3.6"),
                0,
                new List<Variable>(),
                DefaultPrivacyProvider.DefaultPair,
                0x10000,
                new OctetString(ByteTool.Convert("80001F8880E9630000D61FF449")),
                0,
                0
               );
trap.Send(new IPEndPoint(IPAddress.Parse("192.168.1.2"), 162));

INFORM Operation

Comparing to sending TRAP v2 messages, it is common to send INFORM messages.

The following code shows how to send an INFORM message to an SNMP manager/trap listener located at 192.168.1.2,

Messenger.SendInform(
                    0,
                    VersionCode.V3,
                    new IPEndPoint(IPAddress.Parse("192.168.1.2"), 162),
                    new OctetString("neither"),
                    new ObjectIdentifier(new uint[] { 1, 3, 6 }),
                    0,
                    new List<Variable>(),
                    2000,
                    DefaultPrivacyProvider.DefaultPair,
                    report);


To help you understand how to use the API provided by #SNMP Library, there are more sample projects you can find under Samples folder in source code package. Both C# and VB.NET samples are available.

The help documentation is available online at http://help.sharpsnmp.com.

Last edited Jan 27, 2016 at 11:58 AM by lextm, version 4