snmp4j snmpwalk with Community String Indexing

Question

How to do a snmpwalk with snmp4j and Community String Indexing?

I can do a Community String Indexing by changing the community String like public@123 (123 is the vlanId)

But this works only with snmpget !!??:

public ResponseEvent get(OID oids) throws IOException {
    PDU pdu = new PDU();
    pdu.add(new VariableBinding(oid));
    pdu.setType(PDU.GETNEXT);
    ResponseEvent event = snmp.send(pdu, getTarget(), null);
}

private Target getTarget() {
    Address targetAddress = GenericAddress.parse(sw.getAddress());
    CommunityTarget target = new CommunityTarget();
    target.setCommunity(new OctetString(communityString));
    target.setAddress(targetAddress);
    target.setRetries(2);
    target.setTimeout(1500);
    target.setVersion(SnmpConstants.version2c);
    return target;
}

But when I try to do a snmpwalk like this i get a timeout

public HashMap<String, String> snmpWalk(String strOid) throws IOException {
    OID oid = new OID(strOid);
    TreeUtils treeUtils = new TreeUtils(snmp, new DefaultPDUFactory());
    HashMap<String, String> snmpResult = new HashMap<String, String>();
    List<TreeEvent> events = treeUtils.getSubtree(getTarget(), oid);
    // some more code ...
}

Answer 1

I fixed the problem by writing a SNMP-walk method using GETBULK

It is important to set the maxRepetitions and maxSizeResponsePDU I use this values:

/** maxRepetitions needs to be set for BULKGET to work<br>
 * it defines the maximum lines/results returned for one request. 
 */
private int maxRepetitions = 50;

/** maxSizeResponsePDU needs to be set for BULKGET to work */
private int maxSizeResponsePDU = 65535;

public HashMap<String, String> snmpWalk (String startOid) throws IOException{
    //String startOid = "1.3.6.1.4.1.9.9.46.1.3.1.1.4.1"; 
    String oid = startOid;
    HashMap<String, String> varBindings = new HashMap<String, String>();

    while (oid.startsWith(startOid)) {
        PDU pdu = getVariableBinding(new OID(oid), PDU.GETBULK);
        if (pdu == null || pdu.size() == 0) return varBindings;

        for (int i=0; i<pdu.size(); i++) {
            VariableBinding var = pdu.get(i);
            if (var == null) return varBindings;

            oid = var.getOid().toString();
            if (oid.startsWith(startOid)) {
                varBindings.put(oid, var.getVariable().toString());
            } else {
                return varBindings;
            }
        }
    }
    return varBindings;
}

/**
 * Method which takes a single OID and returns the response from the agent
 * as a String.
 * 
 * @param oid
 * @return
 * @throws IOException
 */
public PDU getVariableBinding(OID oid, int type) throws IOException {
    ResponseEvent event = get(new OID[] { oid }, type);

    if (event == null || event.getResponse() == null) {
        warn(oid);
        return null;
    }

    return event.getResponse();
}

public ResponseEvent get(OID oids[], int type) throws IOException {
    PDU pdu = new PDU();
    for (OID oid : oids) {
        pdu.add(new VariableBinding(oid));
    }
    pdu.setType(type);

    pdu.setMaxRepetitions(maxRepetitions); // This makes GETBULK work as expected

    ResponseEvent event = snmp.send(pdu, getTarget(), null);
    if (event != null) {
        return event;
    }
    throw new RuntimeException("GET timed out");
}

private Target getTarget() {
    Address targetAddress = GenericAddress.parse(sw.getAddress());
    CommunityTarget target = new CommunityTarget();
    target.setCommunity(new OctetString(communityString));
    target.setAddress(targetAddress);
    target.setRetries(2);
    target.setTimeout(3000);
    target.setVersion(SnmpConstants.version2c);

    target.setMaxSizeRequestPDU(maxSizeResponsePDU); // This makes GETBULK work as expected

    return target;
}

Answer 2

With SNMP4J there is the TreeUtils class which provides already the "walk" functionality you implemented here and which sets reasonable defaults for the maxRepetitions and nonRepeaters fields.