[SNMP4J] java.lang.NullPointerException: Context engine ID must not be null

[Frank Fock]

Hi Philippe,
It's how I wrote. You are not specifying the instance sub-identifiers. A GETNEXT will *never* return a noSuchInstance error! (If the agent is SNMP standard conform)
Best regards 
Frank

> Am 11.08.2016 um 11:03 schrieb FLORENT Philippe <Philippe.FLORENT at edenred.com>:
> 
> Please help, I am really struggling with this, that OID exists, no matter I use GT or GETNEXT, it return "no such instance"
> 
> If I look the infos on that oid : .1.3.6.1.2.1.4.20.1.2
> 
> Walk:
> -------
> IP-MIB::ipAdEntIfIndex.127.0.0.1 = INTEGER: 1
> IP-MIB::ipAdEntIfIndex.192.168.1.128 = INTEGER: 2
> 
> snmptranslate -Td  :
> -------------------------
> IP-MIB::ipAdEntIfIndex
> ipAdEntIfIndex OBJECT-TYPE
>  -- FROM    IP-MIB
>  SYNTAX    INTEGER (1..2147483647) 
>  MAX-ACCESS    read-only
>  STATUS    deprecated
>  DESCRIPTION    "The index value which uniquely identifies the interface to
>            which this entry is applicable.  The interface identified by
>            a particular value of this index is the same interface as
>            identified by the same value of the IF-MIB's ifIndex."
> ::= { iso(1) org(3) dod(6) internet(1) mgmt(2) mib-2(1) ip(4) ipAddrTable(20) ipAddrEntry(1) 2 }
> 
> 
> 
> 
> 
> -----Original Message-----
> From: Frank Fock [mailto:fock at agentpp.com] 
> Sent: jeudi 11 août 2016 10:26
> To: FLORENT Philippe
> Cc: snmp4j at agentpp.org
> Subject: Re: [SNMP4J] java.lang.NullPointerException: Context engine ID must not be null
> 
> Hi,
> If walk (which is a GETNEXT in fact) and GET behave differently then most likely you are using the wrong OID (wrong instance identifier). Sometimes the agent is broken too.
> In your case, you should put the Snmp instance in listen mode to receive answers from the agent. See FAQ for details.
> Best regards 
> Frank
> 
>> Am 11.08.2016 um 09:29 schrieb FLORENT Philippe <Philippe.FLORENT at edenred.com>:
>> 
>> Hello everyone,
>> 
>> 
>> -          Doing a get on some OID  give me "unkown instance" although they work with snmpwalk on the command line and GET works with mib explorer
>> 
>> 
>> 
>> -          So I try to implement an snmp walk in snmp4j but I keep getting that error
>> 
>> Here is the code
>> 
>> I tried to use request.getContextEngineID(), but it is also null
>> 
>> public class SnmpProber
>> {
>>  private Snmp snmp;
>>   private UserTarget target;
>> 
>>   private byte[] authEngineId0=null;
>> 
>>   public SnmpProber(String ipAddress,String port,String userName,String authPass,String privPass)
>>   {
>>       try
>>       {
>>           Address targetAddress = GenericAddress.parse("udp:"+ipAddress+"/"+port);
>>           TransportMapping transport = new DefaultUdpTransportMapping();
>>           snmp = new Snmp(transport);
>>           USM usm = new USM(SecurityProtocols.getInstance(),new OctetString(MPv3.createLocalEngineID()), 0);
>>           SecurityModels.getInstance().addSecurityModel(usm);
>>           transport.listen();
>> 
>>           target = new UserTarget();
>>           target.setAddress(targetAddress);
>>           target.setRetries(1);
>>           target.setTimeout(5000);
>>           target.setVersion(SnmpConstants.version3);
>>           target.setSecurityLevel(SecurityLevel.AUTH_PRIV);
>>           target.setSecurityName(new OctetString(userName));
>> 
>>           authEngineId0 = snmp.discoverAuthoritativeEngineID(target.getAddress(), 5000);
>> 
>>           if(authEngineId0==null)
>>               System.out.println("cannot connect");
>>           else
>>           {
>>               // add user to the USM
>>               UsmUser usmUser=new UsmUser(new OctetString(userName),
>>                                     AuthSHA.ID,
>>                                     new OctetString(authPass),
>>                                     PrivAES128.ID,
>>                                     new OctetString(privPass));
>> 
>>               snmp.getUSM().addUser(new OctetString("v3DefaultUser"),
>>                                     new OctetString(authEngineId0),
>>                                     usmUser);
>>           }
>>       } catch (IOException ex) {
>>           Logger.getLogger(SnmpProber.class.getName()).log(Level.SEVERE, null, ex);
>>       }
>>   }
>> 
>>   public boolean isOk()
>>   {
>>       return authEngineId0!=null;
>>   }
>> 
>>   class WalkCounts {
>>       public int requests;
>>       public int objects;
>>   }
>> 
>>   public List<VariableBinding> walk(String oid)
>>   {
>>       final List<VariableBinding> result;
>>       result = new LinkedList<VariableBinding>();
>>       ScopedPDU request;
>>       request = new ScopedPDU();
>>       request.setType(PDU.GETNEXT);
>> 
>>       request.add(new VariableBinding(new OID(oid)));
>> 
>>       request.setNonRepeaters(0);
>> 
>>       OID rootOID = request.get(0).getOid();
>> 
>>       final WalkCounts counts = new WalkCounts();
>>       final long startTime = System.currentTimeMillis();
>>       TreeUtils treeUtils = new TreeUtils(snmp, new DefaultPDUFactory());
>> 
>>       TreeListener treeListener = new TreeListener()
>>       {
>>           public boolean next(TreeEvent e) {
>>               counts.requests++;
>> 
>>               if (e.getVariableBindings() != null) {
>>                   VariableBinding[] vbs = e.getVariableBindings();
>>                   counts.objects += vbs.length;
>>                   for (int i = 0; i < vbs.length; i++) {
>>                       if (result != null) {
>>                           result.add(vbs[i]);
>>                       }
>>                       System.out.println(vbs[i].toString());
>>                   }
>>               }
>>               return true;
>>           }
>> 
>>           @Override
>>           public void finished(TreeEvent e) {
>>               if ((e.getVariableBindings() != null)
>>                       && (e.getVariableBindings().length > 0)) {
>>                   next(e);
>>               }
>> 
>>               System.out.println("Total requests sent:    "+ counts.requests);
>>               System.out.println("Total objects received: "+ counts.objects);
>>               System.out.println("Total walk time:        "+ (System.currentTimeMillis() - startTime)+ " milliseconds");
>> 
>>               if (e.isError()) {
>>                   System.err.println("The following error occurred during walk:");
>>                   System.err.println(e.getErrorMessage());
>>               }
>>               synchronized (this) {
>>                   this.notify();
>>               }
>>           }
>> 
>>           @Override
>>           public boolean isFinished() {
>>               return true;
>>           }
>>       };
>> 
>>       synchronized (treeListener)
>>       {
>>           treeUtils.getSubtree(target, rootOID, null, treeListener);  <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< exception here
>>           try
>>           {
>>               treeListener.wait();
>>           }
>>           catch (InterruptedException ex)
>>           {
>>               System.out.println("Tree retrieval interrupted: "+ex);
>>               Thread.currentThread().interrupt();
>>           }
>>       }
>> 
>>       return result;
>>   }
>> 
>>   public void Release()
>>   {
>>       try {
>>           snmp.close();
>>       } catch (IOException ex) {
>>           Logger.getLogger(SnmpProber.class.getName()).log(Level.SEVERE, null, ex);
>>       }
>>   }
>> }
>> 
>> 
>> 
>> 
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