How To Send SNMP Trap with Variable Bindings from Testdll.dll

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The following sample code composes the toasterControl MIB (.1.3.6.1.4.1.12.2.3.0), toasterDoness MIB (.1.3.6.1.4.1.12.2.4.0) and toastType MIB(.1.3.6.1.4.1.12.2.5.0) variables into a variable binding list and passes the list back to the SNMP service.

You need to modify the following three steps in the Testdll.dll SNMP extension agent sample:

1. Include the mgmtapi.h header file to your testdll.c file as follows:

         #include <snmp.h>
         #include <mgmtapi.h>
   						

2. Replace the SnmpExtensionTrap entry point in the file testdll.c with the following code:

         BOOL WINAPI SnmpExtensionTrap(
            OUT AsnObjectIdentifier *enterprise,
            OUT AsnInteger          *genericTrap,
            OUT AsnInteger          *specificTrap,
            OUT AsnTimeticks        *timeStamp,
            OUT RFC1157VarBindList  *variableBindings)
         {
            // The following define data inserted into the trap below.
   
            static UINT OidList[]  = { 1, 3, 6, 1, 4, 1, 12, 2 };
            static UINT OidListLen = 8;
   
   
            // The following variable is used for the simulation. It allows a
            // single trap to be generated and causes FALSE to be returned,
            // indicating no more traps.
   
            static whichTime = 0;
            RFC1157VarBind* pVB; // Variable binding.
            AsnObjectIdentifier reqObject;
            int MIB_num_variables = 3; // Hard coded for testing.
   
            // The following if/else support the simulation.
   
            if (whichTime == 0)
            {
               whichTime = 1;    // Supports the simulation.
   
   
            // Communicate the trap data to the Extendible Agent.
   
               enterprise->idLength = OidListLen;
               enterprise->ids = OidList;
   
               *genericTrap      = SNMP_GENERICTRAP_ENTERSPECIFIC;
   
               *specificTrap     = 1;   // ToasterControl Up trap.
   
               *timeStamp        = GetCurrentTime() - dwTimeZero;
   
               // Allocate space for the Variable Bindings.
               pVB = SnmpUtilMemAlloc(MIB_num_variables *
                                      sizeof(RFC1157VarBind));
               memset(pVB, 0, MIB_num_variables * sizeof(RFC1157VarBind));
               if (pVB == NULL)
               {
                  whichTime = 0;
                  return FALSE;
               }
               // Copy the VarBindList.
               variableBindings->list = pVB;
               variableBindings->len  = MIB_num_variables;
   
   
               // ToasterControl.
               if (SnmpMgrStrToOid(".1.3.6.1.4.1.12.2.3.0", &reqObject) == 0)
               {
                  whichTime = 0;
                  SnmpUtilMemFree(variableBindings->list);
                  variableBindings->list = NULL;
                  variableBindings->len  = 0;
                  return FALSE;
               }
   
               pVB->name = reqObject; // NOTE: Structure copy.
               pVB->value.asnType = ASN_INTEGER;
               // Toaster control in down position.
               pVB->value.asnValue.number = 2;
               pVB++;
   
               // ToasterDoness.
               if (SnmpMgrStrToOid(".1.3.6.1.4.1.12.2.4.0", &reqObject) == 0)
               {
                  whichTime = 0;
   
                  pVB--;
                  // Free previous allocated oid.
                  SnmpUtilOidFree(&(pVB->name));
                  SnmpUtilMemFree(variableBindings->list);
                  variableBindings->list = NULL;
                  variableBindings->len  = 0;
                  return FALSE;
               }
   
               pVB->name = reqObject; // NOTE!  structure copy
               pVB->value.asnType = ASN_INTEGER;
               pVB->value.asnValue.number = 1; // Toaster Doness is lightest.
               pVB++;
   
               // ToastType.
               if (SnmpMgrStrToOid(".1.3.6.1.4.1.12.2.5.0", &reqObject) == 0)
               {
                  whichTime = 0;
   
                  pVB--;
                  // Free previous allocated oid.
                  SnmpUtilOidFree(&(pVB->name));
                  pVB--;
                  // Free previous allocated oid.
                  SnmpUtilOidFree(&(pVB->name));
   
                  SnmpUtilMemFree(variableBindings->list);
                  variableBindings->list = NULL;
                  variableBindings->len  = 0;
                  return FALSE;
               }
   
               pVB->name = reqObject; // NOTE: Structure copy.
               pVB->value.asnType = ASN_INTEGER;
               pVB->value.asnValue.number = 3; // Wonder-bread(3).
   
               // Indicate that valid trap data exists in the parameters.
               return TRUE;
            }
            else
            {
               // The previous allocated variable binding has been freed
               // by SNMP service.
               whichTime = 0;    // Supports the simulation.
   
               // Indicate that no more traps are available, and parameters do
               // not refer to any valid data.
   
               return FALSE;
            }
   
         } // End SnmpExtensionTrap().
   						

3. Modify the Makefile to add SNMP Management library mgmtapi.lib to the link command.

Do the following to see the trap data sent by the code sample:

1. Configure your SNMP service to send trap to localhost.
2. Run the snmputil.exe SNMP manager from Platform SDK sample in console A as follows:

         C:\>snmputil trap
         snmputil: listening for traps...
   						

3. Run another instance of snmputil.exe in another console as follows:

         C:\>snmputil walk localhost public .1.3.6.1.4.1.12.2
         Variable = .iso.org.dod.internet.private.enterprises.12.2.1.0
         Value    = OCTET STRING - Microsoft Corporation
   
         Variable = .iso.org.dod.internet.private.enterprises.12.2.2.0
         Value    = OCTET STRING - Example SNMP Extension Agent for
                    Windows/NT  (TOASTER-MIB).
   
         Variable = .iso.org.dod.internet.private.enterprises.12.2.3.0
         Value    = INTEGER - 1
   
         Variable = .iso.org.dod.internet.private.enterprises.12.2.4.0
         Value    = INTEGER - 2
   
         Variable = .iso.org.dod.internet.private.enterprises.12.2.5.0
         Value    = INTEGER - 3
   
         End of MIB subtree.
   						

4. You will see the trap data in console A as follows:

         snmputil: trap generic=6 specific=1
           from -> xxx.xxx.xxx.xxx
         Variable = .iso.org.dod.internet.private.enterprises.12.2.3.0
         Value    = INTEGER - 2
         Variable = .iso.org.dod.internet.private.enterprises.12.2.4.0
         Value    = INTEGER - 1
         Variable = .iso.org.dod.internet.private.enterprises.12.2.5.0
         Value    = INTEGER - 3
   						

NOTE: This code sample will not work under Windows 9x platforms because SnmpMgrStrToOid is a function exported from mgmtapi.lib, which is not available in the Windows 9x platforms. To work around this, you have to provide a similar utility on your own.