SNMP Walk Example using SNMP4J

This article is pretty straightforward. It’s an SNMP walk example using SNMP4J. SNMP is used in managing and monitoring network devices. It is an Internet standard protocol for managing devices on IP networks.

1. Tools and Prerequisites

1. SNMP4J library
2. Mars Eclipse

2. Create the Project

You may skip this process because this is a fairly simple example which can be made using a text editor. We’ll just do a quick Java project creation through Eclipse. Click on File -> New -> Java Project to create the project. Then create the com.javacodegeeks.example package. Next, create an empty SnmpWalk class. We’re not done yet. We have to add the SNMP4J library. Right-click on the project and go to Build Path -> Configure Build Path, then Libraries Tab -> Add External Jars… and add snmp4j-2.5.6.jar (latest version as of this writing).

3. Java Code and Code Walkthrough

The Java code below shows an SNMP walk on the ifTable of the interfaces a certain device. It starts out by creating the CommunityTarget object. This contains the community string, the target IP and port, the number of retries, the timeout value, and the SNMP version being used.
The doWalk method accepts the ifTable OID and the CommunityTarget object as parameters. A more detailed explanation of this method is described below. Lastly, the result is then printed to the console.

SnmpWalk.java

package com.javacodegeeks.example;

import java.io.IOException;
import java.util.List;
import java.util.Map;
import java.util.TreeMap;

import org.snmp4j.CommunityTarget;
import org.snmp4j.Snmp;
import org.snmp4j.Target;
import org.snmp4j.TransportMapping;
import org.snmp4j.mp.SnmpConstants;
import org.snmp4j.smi.Address;
import org.snmp4j.smi.GenericAddress;
import org.snmp4j.smi.OID;
import org.snmp4j.smi.OctetString;
import org.snmp4j.smi.VariableBinding;
import org.snmp4j.transport.DefaultUdpTransportMapping;
import org.snmp4j.util.DefaultPDUFactory;
import org.snmp4j.util.TreeEvent;
import org.snmp4j.util.TreeUtils;

public class SnmpWalk {

	public static void main(String[] args) throws Exception {
		CommunityTarget target = new CommunityTarget();
		target.setCommunity(new OctetString("public"));
		target.setAddress(GenericAddress.parse("udp:x.x.x.x/161")); // supply your own IP and port
		target.setRetries(2);
		target.setTimeout(1500);
		target.setVersion(SnmpConstants.version2c);
		
		Map<String, String> result = doWalk(".1.3.6.1.2.1.2.2", target); // ifTable, mib-2 interfaces

		for (Map.Entry<String, String> entry : result.entrySet()) {
			if (entry.getKey().startsWith(".1.3.6.1.2.1.2.2.1.2.")) {
				System.out.println("ifDescr" + entry.getKey().replace(".1.3.6.1.2.1.2.2.1.2", "") + ": " + entry.getValue());
			}
			if (entry.getKey().startsWith(".1.3.6.1.2.1.2.2.1.3.")) {
				System.out.println("ifType" + entry.getKey().replace(".1.3.6.1.2.1.2.2.1.3", "") + ": " + entry.getValue());
			}
		}
	}

	public static Map<String, String> doWalk(String tableOid, Target target) throws IOException {
		Map<String, String> result = new TreeMap<>();
		TransportMapping<? extends Address> transport = new DefaultUdpTransportMapping();
		Snmp snmp = new Snmp(transport);
		transport.listen();

		TreeUtils treeUtils = new TreeUtils(snmp, new DefaultPDUFactory());
		List events = treeUtils.getSubtree(target, new OID(tableOid));
		if (events == null || events.size() == 0) {
			System.out.println("Error: Unable to read table...");
			return result;
		}

		for (TreeEvent event : events) {
			if (event == null) {
				continue;
			}
			if (event.isError()) {
				System.out.println("Error: table OID [" + tableOid + "] " + event.getErrorMessage());
				continue;
			}

			VariableBinding[] varBindings = event.getVariableBindings();
			if (varBindings == null || varBindings.length == 0) {
				continue;
			}
			for (VariableBinding varBinding : varBindings) {
				if (varBinding == null) {
					continue;
				}
				
				result.put("." + varBinding.getOid().toString(), varBinding.getVariable().toString());
			}

		}
		snmp.close();

		return result;
	}

}

You’ll need to provide your own SNMP agent IP address and port (highlighted). We are using SNMP version 2c. This example will walk the mib2.interfaces.ifTable. It will stop the walk when it is finished walking the ifTable tree (the VariableBinding OID does not have the same prefix). Once the walk is finished, the interface description and type are then printed out.

The TreeUtils (highlighted) API does the heavy lifting for us. TreeUtils retrieves a subtree of management values using SNMP GetNext Requests. GetNext is a request to discover available variables and their values. This process have been abstracted by this API. We are so lucky.

The results are then returned as a Map with the OID as the key and the values as type String.

4. Output

Your output should look something like the one below. You can verify it using a MIB browser.

Console Output

ifDescr.1: igb0
ifDescr.10: lo0
ifDescr.11: ovpns1
ifDescr.12: ovpnc2
ifDescr.2: igb1
ifDescr.3: igb2
ifDescr.4: igb3
ifDescr.5: igb4
ifDescr.6: igb5
ifDescr.7: pflog0
ifDescr.8: pfsync0
ifDescr.9: enc0
ifType.1: 6
ifType.10: 24
ifType.11: 23
ifType.12: 23
ifType.2: 6
ifType.3: 6
ifType.4: 6
ifType.5: 6
ifType.6: 6
ifType.7: 246
ifType.8: 247
ifType.9: 244

5. Summary of the SNMP Walk Example using SNMP4J

In this example, we learned to perform an SNMP walk using SNMP4J’s TreeUtils API. TreeUtils retrieved the subtree of management values for us. The multiple SNMP GetNext Requests have been abstracted by the API. Our programming has been made easier. A more optimized way of walking a MIB tree is to use the SNMP GetBulk Request introduced in SNMP version 2. With the GetBulk Request, the manger sends a single request for multiple iterations of the GetNext Request which is performed in the agent’s side. Whereas the SNMP walk performs multiple requests to the agent thus adding load on the network traffic.

6. Download the Source Code

This is an example of an SNMP Walk using SNMP4J.

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