Re: [Mibble-users] snmpwalk and the loading the MIB files

[Per Cederberg]

Hi Punit,

I see you are using the undocumented internal Mibble API
for SNMP that the Mibble browser is also using. I have no
problem with this, but you should be aware that it is
unsupported and may change without notice in future
versions.

The problem you are having is that table OID:s are a bit
special in SNMP. In general and as your code assumes, the
MIB file contains all OID:s and they can be retrieved
through the ObjectIdentifierValue class. However, when
tables are being used, the SNMP agent appends the table
row index to the end of the OID.

So in your case enterprises.5596.10.3.4.1.3 is the OID for
the string column (in the table), whereas the appended .1
.2 and .3 represent the values on the different rows in a
the table. That is, the "children" to the display string
OID that you see are in fact not children at all, but
different table rows.

The solution here is to use the OID returned by the
getNext() operation as input for another getNext() call,
effectively letting the SNMP agent step through the MIB
instead of the ObjectIdentifierValue class (that doesn't
know how many or which rows exist). In the method 
SnmpPanel.Operation.runGetAll() Mibble implements this for
the Mibble browser:

            do {
                response = manager.getNext(oid);
                oid = response.getOid(0);
                if (oid.startsWith(request.getOid())) {
                    ...
                } else {
                    ...
                    stopped = true;
                }
            } while (!stopped);

Hope this helps!

/Per

On mon, 2004-12-13 at 12:56 -0800, punit gupta wrote:
> Hello Sir,
> 
> I am building an application to do snmpwalk for a
> given OID. It works fine except in the case when a
> particular OID is of type DisplayString. I am not able
> to get the children of the such ObjectIdentifierValue
> objects. For example if I do the snmpwalk using the
> linux's snmpwalk command with
> "1.3.6.1.4.1.5596.10.3.4.1.3" for a given ID, it gives
> me following output:
> 
> SNMPv2-SMI::enterprises.5596.10.3.4.1.3.1 = STRING:
> "130.207.179.65"
> SNMPv2-SMI::enterprises.5596.10.3.4.1.3.2 = ""
> SNMPv2-SMI::enterprises.5596.10.3.4.1.3.3 = ""
> SNMPv2-SMI::enterprises.5596.10.3.4.1.3.4 = ""
> 
> When I try the same functionality with my custom built
> snmpwalk using the mibble api, it only gives me the
> first one correctly. Here is the code:
> 
> private static void printOid(ObjectIdentifierValue
> objectidentifiervalue)
> {
>  if(objectidentifiervalue.getChildCount() == 0)
>   try
>   {
>    SnmpManager snmpmanager = SnmpManager.createSNMPv1
> (host, port, community);
>    String s = objectidentifiervalue.toString();
>    
>    try
>    {
>    SnmpResponse snmpresponse = snmpmanager.getNext(s);
>   
> System.out.println(snmpresponse.getOidsAndValues());
>    }
>    catch(SnmpException snmpexception1)
>    {
>       System.out.println("error occured");
>    }
>   }
>   catch(SnmpException snmpexception)
>   {
>   System.out.println("snmpManager can not be created
> :" + snmpexception.getMessage());
>   }
> 
>   for(int i = 0; i <
> objectidentifiervalue.getChildCount(); i++)
>  {
>    printOid(objectidentifiervalue.getChild(i));
>   }
>  }
> 
> 
> When I use the getNext method of SNMPManager on a OID
> which is "child" of a OID Of type DisplayString, it
> still gives me the first "child" of the OID
> (displayString).
> 
> I think it has something to do with DisplayString.
> Since the children of DisplayString type OID are not
> listed in the mib (right??), they do not appear in the
> getChildren method also.
> 
> Any suggestions would be appreciated.
> Thanks bunch,
> -Punit.