net-snmp

This module implements version 1 and 2c of the Simple Network Management Protocol (SNMP).

This module is installed using node package manager (npm):

npm install net-snmp

It is loaded using the require() function:

var snmp = require ("net-snmp");

Sessions to remote hosts can then be created and used to perform SNMP requests and send SNMP traps or informs:

var session = snmp.createSession ("127.0.0.1", "public");

var oids = ["1.3.6.1.2.1.1.5.0", "1.3.6.1.2.1.1.6.0"];

session.get (oids, function (error, varbinds) {
    if (error) {
        console.error (error);
    } else {
        for (var i = 0; i < varbinds.length; i++)
            if (snmp.isVarbindError (varbinds[i]))
                console.error (snmp.varbindError (varbinds[i]))
            else
                console.log (varbinds[i].oid + " = " + varbinds[i].value);
    }
});

session.trap (snmp.TrapType.LinkDown, function (error) {
    if (error)
        console.error (error);
});

Standards Compliance

This module aims to be fully compliant with the following RFCs:

• 1155 - Structure and Identification of Management Information
• 1098 - A Simple Network Management Protocol (version 1)
• 2578 - Structure of Management Information Version 2 (SMIv2)
• 3416 - Simple Network Management Protocol (SNMP) (version 2c)

However, this module does not implement, or export any method that might help to implement, the SNMP version 2c report request type.

Constants

The following sections describe constants exported and used by this module.

snmp.Version1 & snmp.Version2c

These constants are used to specify which of the two versions supported by this module should be used.

snmp.ErrorStatus

This object contains constants for all valid values the error-status field in response PDUs can hold. If when parsing a PDU the error-index field contains a value not defined in this object the constant snmp.ErrorStatus.GeneralError will be used instead of the value in the error-status field. The following constants are defined in this object:

• NoError
• TooBig
• NoSuchName
• BadValue
• ReadOnly
• GeneralError
• NoAccess
• WrongType
• WrongLength
• WrongEncoding
• WrongValue
• NoCreation
• InconsistentValue
• ResourceUnavailable
• CommitFailed
• UndoFailed
• AuthorizationError
• NotWritable
• InconsistentName

snmp.ObjectType

This object contains constants used to specify syntax for varbind objects, e.g.:

var varbind = {
    oid: "1.3.6.1.2.1.1.4.0",
    type: snmp.ObjectType.OctetString,
    value: "[email protected]"
};

The following constants are defined in this object:

• Boolean
• Integer
• OctetString
• Null
• OID
• IpAddress
• Counter
• Gauge
• TimeTicks
• Opaque
• Integer32
• Counter32
• Gauge32
• Unsigned32
• Counter64
• NoSuchObject
• NoSuchInstance
• EndOfMibView

snmp.TrapType

This object contains constants used to specify a type of SNMP trap. These constants are passed to the trap() and inform() methods exposed by the Session class. The following constants are defined in this object:

• ColdStart
• WarmStart
• LinkDown
• LinkUp
• AuthenticationFailure
• EgpNeighborLoss
• EnterpriseSpecific

OID Strings & Varbinds

Some parts of this module accept simple OID strings, e.g.:

var oid = "1.3.6.1.2.1.1.5.0";

Other parts take an OID string, it's type and value. This is collectively referred to as a varbind, and is specified as an object, e.g.:

var varbind = {
    oid: "1.3.6.1.2.1.1.5.0",
    type: snmp.ObjectType.OctetString,
    value: new Buffer ("host1")
};

The type parameter is one of the constants defined in the snmp.ObjectType object.

The JavaScript true and false keywords are used for the values of varbinds with type Boolean.

All integer based types are specified as expected (this includes Integer, Counter, Gauge, TimeTicks, Integer32, Counter32, Gauge32, and Unsigned32), e.g. -128 or 100.

Since JavaScript does not offer full 64 bit integer support objects with type Counter64 cannot be supported in the same way as other integer types, instead Node.js Buffer objects are used. Users are responsible for producing (i.e. for set() requests) and consuming (i.e. the varbinds passed to callback functions) Buffer objects. That is, this module does not work with 64 bit integers, it simply treats them as opaque Buffer objects.

Dotted decimal strings are used for the values of varbinds with type OID, e.g. 1.3.6.1.2.1.1.5.0.

Dotted quad formatted strings are used for the values of varbinds with type IpAddress, e.g. 192.168.1.1.

Node.js Buffer objects are used for the values of varbinds with type Opaque and OctetString. For varbinds with type OctetString this module will accept JavaScript strings, but will always give back Buffer objects.

The NoSuchObject, NoSuchInstance and EndOfMibView types are used to indicate an error condition. Currently there is no reason for users of this module to to build varbinds using these types.

Callback Functions & Error Handling

Most of the request methods exposed by this module require a mandatory callback function. This function is called once a request has been processed. This could be because an error occurred when processing the request, a trap has been dispatched or a successful response was received.

The first parameter to every callback is an error object. In the case no error occurred this parameter will be "null" indicating no error, e.g.:

function responseCb (error, varbinds) {
    if (error) {
        console.error (error);
    } else {
        // no error, do something with varbinds
    }
}

When defined, the error parameter is always an instance of the Error class, or a sub-class described in one of the sub-sections contained in this section.

The semantics of error handling is slightly different between SNMP version 1 and 2c. In SNMP version 1 if an error occurs when calculating the value for one OID the request as a whole will fail, i.e. no OIDs will have a value.

This failure manifests itself within the error-status and error-index fields of the response. When the error-status field in the response is non-zero, i.e. not snmp.ErrorStatus.NoError the callback will be called with error defined detailing the error.

Requests made with SNMP version 1 can simply assume all OIDs have a value when no error object is passed to the callback, i.e.:

var oids = ["1.3.6.1.2.1.1.5.0", "1.3.6.1.2.1.1.6.0"];

session.get (oids, function (error, varbinds) {
    if (error) {
        console.error (error.toString ());
    } else {
        var sysName = varbinds[0].value; // this WILL have a value
    }
});

In SNMP version 2c instead of using the error-status and error-index fields of the response to signal an error, the value for the varbind placed in the response for an OID will have an object syntax describing an error. The error-status and error-index fields of the response will indicate the request was successul, i.e. snmp.ErrorStatus.NoError.

This changes the way in which error checking is performed in the callback. When using SNMP version 2c each varbind must be checked to see if its value was computed and returned successfully:

var oids = ["1.3.6.1.2.1.1.5.0", "1.3.6.1.2.1.1.6.0"];

session.get (oids, function (error, varbinds) {
    if (error) {
        console.error (error.toString ());
    } else {
        if (varbinds[0].type != snmp.ErrorStatus.NoSuchObject
                && varbinds[0].type != snmp.ErrorStatus.NoSuchInstance
                && varbinds[0].type != snmp.ErrorStatus.EndOfMibView) {
            var sysName = varbinds[0].value;
        } else {
            console.error (snmp.ObjectType[varbinds[0].type] + ": "
                    + varbinds[0].oid);
        }
    }
});

This module exports two functions and promotes a specifc pattern to make error checking a little simpler. Firstly, regardless of version in use varbinds can always be checked. This results in a generic callback that can be used for both versions.

The isVarbindError() function can be used to determine if a varbind has an error condition. This function takes a single varbind parameter and returns true if the varbind has an error condition, otherwise false. The exported varbindError() function can then be used to obtain the error string describing the error, which will include the OID for the varbind:

session.get (oids, function (error, varbinds) {
    if (error) {
        console.error (error.toString ());
    } else {
        if (snmp.isVarbindError (varbinds[0])) {
            console.error (snmp.varbindError (varbinds[0]));
        } else {
            var sysName = varbinds[0].value;
        }
    }
});

If the varbindError function is called with a varbind for which isVarbindError would return false, the string NotAnError will be returned appended with the related OID.

The sections following defines the error classes used by this module.

snmp.RequestFailedError

This error indicates a remote host failed to process a request. The exposed message attribute will contain a detailed error message. This error also exposes a status attribute which contains the error-index value from a response. This will be one of the constants defined in the snmp.ErrorStatus object.

snmp.RequestInvalidError

This error indicates a failure to render a request message before it could be sent. The error can also indicate that a parameter provided was invalid. The exposed message attribute will contain a detailed error message.

snmp.RequestTimedOutError

This error states that no response was received for a particular request. The exposed message attribute will contain the value Request timed out.

snmp.ResponseInvalidError

This error indicates a failure to parse a response message. The exposed message attribute will contain a detailed error message.

Using This Module

All SNMP requests are made using an instance of the Session class. This module exports the createSession() function which is used to create instances of the Session class.

snmp.createSession ([target], [community], [options])

The createSession() function instantiates and returns an instance of the Session class:

// Default options
var options = {
    port: 161,
    retries: 1,
    timeout: 5000,
    transport: "udp4",
    trapPort: 162,
    version: snmp.Version1
};

var session = snmp.createSession ("127.0.0.1", "public", options);

The optional target parameter defaults to 127.0.0.1. The optional community parameter defaults to public. The optional options parameter is an object, and can contain the following items:

• port - UDP port to send requests too, defaults to 161
• retries - Number of times to re-send a request, defaults to 1
• sourceAddress - IP address from which SNMP requests should originate, there is no default for this option, the operating system will select an appropriate source address when the SNMP request is sent
• sourcePort - UDP port from which SNMP requests should originate, defaults to an ephemeral port selected by the operation system
• timeout - Number of milliseconds to wait for a response before re-trying or failing, defaults to 5000
• transport - Specify the transport to use, can be either udp4 or udp6, defaults to udp4
• trapPort - UDP port to send traps and informs too, defaults to 162
• version - Either snmp.Version1 or snmp.Version2c, defaults to snmp.Version1

session.on ("close", callback)

The close event is emitted by the session when the sessions underlying UDP socket is closed.

No arguments are passed to the callback.

Before this event is emitted all outstanding requests are cancelled, resulting in the failure of each outstanding request. The error passed back through to each request will be an instance of the Error class with the errors message attribute set to Socket forcibly closed.

The following example prints a message to the console when a sessions underlying UDP socket is closed:

session.on ("close", function () {
    console.log ("socket closed");
});

session.on ("error", callback)

The error event is emitted by the session when the sessions underlying UDP socket emits an error.

The following arguments will be passed to the callback function:

• error - An instance of the Error class, the exposed message attribute will contain a detailed error message.

The following example prints a message to the console when an error occurs with a sessions underlying UDP socket, the session is then closed:

session.on ("error", function (error) {
    console.log (error.toString ());
    session.close ();
});

session.close ()

The close() method closes the sessions underlying UDP socket. This will result in the close event being emitted by the sessions underlying UDP socket which is passed through to the session, resulting in the session also emitting a close event.

The following example closes a sessions underlying UDP socket:

session.close ();

session.get (oids, callback)

The get() method fetches the value for one or more OIDs.

The oids parameter is an array of OID strings. The callback function is called once the request is complete. The following arguments will be passed to the callback function:

• error - Instance of the Error class or a sub-class, or null if no error occurred
• varbinds - Array of varbinds, will not be provided if an error occurred

The varbind in position N in the varbinds array will correspond to the OID in position N in the oids array in the request.

Each varbind must be checked for an error condition using the snmp.isVarbindError() function when using SNMP version 2c.

The following example fetches values for the sysName (1.3.6.1.2.1.1.5.0) and sysLocation (1.3.6.1.2.1.1.6.0) OIDs:

var oids = ["1.3.6.1.2.1.1.5.0", "1.3.6.1.2.1.1.6.0"];

session.get (oids, function (error, varbinds) {
    if (error) {
        console.error (error.toString ());
    } else {
        for (var i = 0; i < varbinds.length; i++) {
            // for version 1 we can assume all OIDs were successful
            console.log (varbinds[i].oid + "|" + varbinds[i].value);
        
            // for version 2c we must check each OID for an error condition
            if (snmp.isVarbindError (varbinds[i]))
                console.error (snmp.varbindError (varbinds[i]));
            else
                console.log (varbinds[i].oid + "|" + varbinds[i].value);
        }
    }
});

session.getBulk (oids, [nonRepeaters], [maxRepetitions], callback)

The getBulk() method fetches the value for the OIDs lexicographically following one or more OIDs in the MIB tree.

The oids parameter is an array of OID strings. The optional nonRepeaters parameter specifies the number of OIDs in the oids parameter for which only 1 varbind should be returned, and defaults to 0. For each remaining OID in the oids parameter the optional maxRepetitions parameter specifies how many OIDs lexicographically following an OID for which varbinds should be fetched, and defaults to 20.

The callback function is called once the request is complete. The following arguments will be passed to the callback function:

• error - Instance of the Error class or a sub-class, or null if no error occurred
• varbinds - Array of varbinds, will not be provided if an error occurred

The varbind in position N in the varbinds array will correspond to the OID in position N in the oids array in the request.

For for the first nonRepeaters items in varbinds each item will be a single varbind. For all remaining items in varbinds each item will be an array of varbinds - this makes it easy to tie response varbinds with requested OIDs since response varbinds are grouped and placed in the same position in varbinds.

Each varbind must be checked for an error condition using the snmp.isVarbindError() function when using SNMP version 2c.

The following example fetches values for the OIDs following the sysContact (1.3.6.1.2.1.1.4.0) and sysName (1.3.6.1.2.1.1.5.0) OIDs, and up to the first 20 OIDs in the ifDescr (1.3.6.1.2.1.2.2.1.2) and ifType (1.3.6.1.2.1.2.2.1.3) columns from the ifTable (1.3.6.1.2.1.2.2) table:

var oids = [
    "1.3.6.1.2.1.1.4.0",
    "1.3.6.1.2.1.1.5.0",
    "1.3.6.1.2.1.2.2.1.2",
    "1.3.6.1.2.1.2.2.1.3"
];

var nonRepeaters = 2;

session.getNext (oids, nonRepeaters, function (error, varbinds) {
    if (error) {
        console.error (error.toString ());
    } else {
        // step through the non-repeaters which are single varbinds
        for (var i = 0; i < nonRepeaters; i++) {
            if (i >= varbinds.length)
                break;

            if (snmp.isVarbindError (varbinds[i]))
                console.error (snmp.varbindError (varbinds[i]));
            else
                console.log (varbinds[i].oid + "|" + varbinds[i].value);
        }

        // then step through the repeaters which are varbind arrays
        for (var i = nonRepeaters; i < varbinds.length; i++) {
            for (var j = 0; j < varbinds[i].length; j++) {
                if (snmp.isVarbindError (varbinds[i][j]))
                    console.error (snmp.varbindError (varbinds[i][j]));
                else
                    console.log (varbinds[i][j].oid + "|"
                    		+ varbinds[i][j].value);
            }
    }
});

session.getNext (oids, callback)

The getNext() method fetches the value for the OIDs lexicographically following one or more OIDs in the MIB tree.

The oids parameter is an array of OID strings. The callback function is called once the request is complete. The following arguments will be passed to the callback function:

• error - Instance of the Error class or a sub-class, or null if no error occurred
• varbinds - Array of varbinds, will not be provided if an error occurred

The varbind in position N in the varbinds array will correspond to the OID in position N in the oids array in the request.

Each varbind must be checked for an error condition using the snmp.isVarbindError() function when using SNMP version 2c.

The following example fetches values for the next OIDs following the sysObjectID (1.3.6.1.2.1.1.1.0) and sysName (1.3.6.1.2.1.1.4.0) OIDs:

var oids = [
    "1.3.6.1.2.1.1.1.0",
    "1.3.6.1.2.1.1.4.0"
];

session.getNext (oids, function (error, varbinds) {
    if (error) {
        console.error (error.toString ());
    } else {
        for (var i = 0; i < varbinds.length; i++) {
            // for version 1 we can assume all OIDs were successful
            console.log (varbinds[i].oid + "|" + varbinds[i].value);
        
            // for version 2c we must check each OID for an error condition
            if (snmp.isVarbindError (varbinds[i]))
                console.error (snmp.varbindError (varbinds[i]));
            else
                console.log (varbinds[i].oid + "|" + varbinds[i].value);
        }
    }
});

session.inform (typeOrOid, [varbinds], [options], callback)

The inform() method sends a SNMP inform.

The typeOrOid parameter can be one of two types; one of the constants defined in the snmp.TrapType object (excluding the snmp.TrapType.EnterpriseSpecific constant), or an OID string.

The first varbind to be placed in the request message will be for the sysUptime.0 OID (1.3.6.1.6.3.1.1.4.1.0). The value for this varbind will be the value returned by the process.uptime () function multiplied by 100 (this can be overridden by providing upTime in the optional options parameter, as documented below).

This will be followed by a second varbind for the snmpTrapOID.0 OID (1.3.6.1.6.3.1.1.4.1.0). The value for this will depend on the typeOrOid parameter. If a constant is specified the trap OID for the constant will be used as supplied for the varbinds value, otherwise the OID string specified will be used as is for the value of the varbind.

The optional varbinds parameter is an array of varbinds to include in the inform request, and defaults to the empty array [].

The optional options parameter is an object, and can contain the following items:

• upTime - Value of the sysUptime.0 OID (1.3.6.1.6.3.1.1.4.1.0) in the inform, defaults to the value returned by the process.uptime () function multiplied by 100

The callback function is called once a response to the inform request has been received, or an error occurred. The following arguments will be passed to the callback function:

• error - Instance of the Error class or a sub-class, or null if no error occurred
• varbinds - Array of varbinds, will not be provided if an error occurred

The varbind in position N in the varbinds array will correspond to the varbind in position N in the varbinds array in the request. The remote host should echo back varbinds and their values as specified in the request, and the varbinds array will contain each varbind as sent back by the remote host.

Normally there is no reason to use the contents of the varbinds parameter since the varbinds are as they were sent in the request.

The following example sends a generic cold-start inform to a remote host, it does not include any varbinds:

session.inform (snmp.TrapType.ColdStart, function (error) {
    if (error)
        console.error (error);
});

The following example sends an enterprise specific inform to a remote host, and includes two enterprise specific varbinds:

var informOid = "1.3.6.1.4.1.2000.1";

var varbinds = [
    {
        oid: "1.3.6.1.4.1.2000.2",
        type: snmp.ObjectType.OctetString,
        value: "Periodic hardware self-check"
    },
    {
        oid: "1.3.6.1.4.1.2000.3",
        type: snmp.ObjectType.OctetString,
        value: "hardware-ok"
    }
];

// Override sysUpTime, specfiying it as 10 seconds...
var options = {upTime: 1000};
session.inform (informOid, varbinds, options, function (error) {
    if (error)
        console.error (error);
});

session.set (varbinds, callback)

The set() method sets the value of one or more OIDs.

The varbinds parameter is an array of varbind objects. The callback function is called once the request is complete. The following arguments will be passed to the callback function:

• error - Instance of the Error class or a sub-class, or null if no error occurred
• varbinds - Array of varbinds, will not be provided if an error occurred

The varbind in position N in the varbinds array will correspond to the varbind in position N in the varbinds array in the request. The remote host should echo back varbinds and their values as specified in the request unless an error occurred. The varbinds array will contain each varbind as sent back by the remote host.

Each varbind must be checked for an error condition using the snmp.isVarbindError() function when using SNMP version 2c.

The following example sets the value of the sysName (1.3.6.1.2.1.1.4.0) and sysLocation (1.3.6.1.2.1.1.6.0) OIDs:

var varbinds = [
    {
        oid: "1.3.6.1.2.1.1.5.0",
        type: snmp.ObjectType.OctetString,
        value: "host1"
    }, {
        oid: "1.3.6.1.2.1.1.6.0",
        type: snmp.ObjectType.OctetString,
        value: "somewhere"
    }
];

session.set (varbinds, function (error, varbinds) {
    if (error) {
        console.error (error.toString ());
    } else {
        for (var i = 0; i < varbinds.length; i++) {
            // for version 1 we can assume all OIDs were successful
            console.log (varbinds[i].oid + "|" + varbinds[i].value);
        
            // for version 2c we must check each OID for an error condition
            if (snmp.isVarbindError (varbinds[i]))
                console.error (snmp.varbindError (varbinds[i]));
            else
                console.log (varbinds[i].oid + "|" + varbinds[i].value);
        }
    }
});

session.subtree (oid, [maxRepetitions], feedCallback, doneCallback)

The subtree() method fetches the value for all OIDs lexicographically following a specified OID in the MIB tree which have the specified OID as there base. For example, the OIDs sysName (1.3.6.1.2.1.1.5.0) and sysLocation (1.3.6.1.2.1.1.6.0) both have the same base system (1.3.6.1.2.1.1) OID.

For SNMP version 1 repeated get() calls are made until the one of the returned OIDs does not use the specified OID as its base. For SNMP version 2c repeated getBulk() calls are made until the one of the returned OIDs does no used the specified OID as its base.

The oid parameter is an OID string. The optional maxRepetitions parameter is passed to getBulk() requests when SNMP version 2c is being used.

This method will not call a single callback once all OID values are fetched. Instead the feedCallback function will be called each time a response is received from the remote host. The following arguments will be passed to the feedCallback function:

• varbinds - Array of varbinds, and will contain at least one varbind

Each varbind must be checked for an error condition using the snmp.isVarbindError() function when using SNMP version 2c.

Once at least one of the returned OIDs does not use the specified OID as its base, or an error has occurred, the doneCallback function will be called. The following arguments will be passed to the doneCallback function:

• error - Instance of the Error class or a sub-class, or null if no error occurred

Once the doneCallback function has been called the request is complete and the feedCallback function will no longer be called.

If the feedCallback function returns a true value when called no more get() or getBulk() method calls will be made and the doneCallback will be called.

The following example fetches all OIDS under the system (1.3.6.1.2.1.1) OID:

var oid = "1.3.6.1.2.1.1";

function doneCb (error) {
    if (error)
        console.error (error.toString ());
}

function feedCb (varbinds) {
    for (var i = 0; i < varbinds.length; i++) {
        if (snmp.isVarbindError (varbinds[i]))
            console.error (snmp.varbindError (varbinds[i]));
        else
            console.log (varbinds[i].oid + "|" + varbinds[i].value);
    }
}

var maxRepetitions = 20;

// The maxRepetitions argument is optional, and will be ignored unless using
// SNMP verison 2c
session.subtree (oid, maxRepetitions, feedCb, doneCb);

session.table (oid, [maxRepetitions], callback)

The table() method fetches the value for all OIDs lexicographically following a specified OID in the MIB tree which have the specified OID as there base, much like the subtree() method.

This method is designed to fetch conceptial tables, for example the ifTable (1.3.6.1.2.1.2.2) table. The values for returned varbinds will be structured into objects to represent conceptual rows. Each row is then placed into an object with the rows index being the key, e.g.:

var table = {
    // Rows keyed by ifIndex (1 and 2 are shown)
    1: {
        // ifDescr (column 2) and ifType (columnd 3) are shown
        2: "interface-1",
        3: 6,
        ...
    },
    2: {
        2: "interface-2",
        3: 6,
        ...
    },
    ...
}

Internally this method calls the subtree() method to obtain the subtree of the specified table.

The oid parameter is an OID string. If an OID string is passed which does not represent a table the resulting object produced to hold table data will be empty, i.e. it will contain no indexes and rows. The optional maxRepetitions parameter is passed to the subtree() request.

The callback function will be called once the entire table has been fetched. The following arguments will be passed to the callback function:

• error - Instance of the Error class or a sub-class, or null if no error occurred
• table - Object containing object references representing conceptual rows keyed by index (e.g. for the ifTable table rows are keyed by ifIndex), each row object will contain values keyed by column number, will not be provided if an error occurred

If an error occurs with any varbind returned by subtree() no table will be passed to the callback function. The reason for failure, and the related OID string (as returned from a call to the snmp.varbindError() function), will be passed to the callback function in the error argument as an instance of the RequestFailedError class.

The following example fetches the ifTable (1.3.6.1.2.1.2.2) table:

var oid = "1.3.6.1.2.1.2.2";

function sortInt (a, b) {
    if (a > b)
        return 1;
    else if (b > a)
        return -1;
    else
        return 0;
}

function responseCb (error, table) {
    if (error) {
        console.error (error.toString ());
    } else {
        // This code is purely used to print rows out in index order,
        // ifIndex's are integers so we'll sort them numerically using
        // the sortInt() function above
        var indexes = [];
        for (index in table)
            indexes.push (parseInt (index));
        indexes.sort (sortInt);
        
        // Use the sorted indexes we've calculated to walk through each
        // row in order
        for (var i = 0; i < indexes.length; i++) {
            // Like indexes we sort by column, so use the same trick here,
            // some rows may not have the same columns as other rows, so
            // we calculate this per row
            var columns = [];
            for (column in table[indexes[i]])
                columns.push (parseInt (column));
            columns.sort (sortInt);
            
            // Print index, then each column indented under the index
            console.log ("row for index = " + indexes[i]);
            for (var j = 0; j < columns.length; j++) {
                console.log ("   column " + columns[j] + " = "
                        + table[indexes[i]][columns[j]]);
            }
        }
    }
}

var maxRepetitions = 20;

// The maxRepetitions argument is optional, and will be ignored unless using
// SNMP verison 2c
session.table (oid, maxRepetitions, responseCb);

session.tableColumns (oid, columns, [maxRepetitions], callback)

The tableColumns() method implements the same interface as the table() method. However, only the columns specified in the columns parameter will be in the resulting table.

This method should be used when only selected columns are required, and will be many times faster than the table() method since a much smaller amount of data will be fected.

The following example fetches the ifTable (1.3.6.1.2.1.2.2) table, and specifies that only the ifDescr (1.3.6.1.2.1.2.2.1.2) and ifPhysAddress (1.3.6.1.2.1.2.2.1.6) columns should actually be fetched:

var oid = "1.3.6.1.2.1.2.2";
var columns = [2, 6];

function sortInt (a, b) {
    if (a > b)
        return 1;
    else if (b > a)
        return -1;
    else
        return 0;
}

function responseCb (error, table) {
    if (error) {
        console.error (error.toString ());
    } else {
        // This code is purely used to print rows out in index order,
        // ifIndex's are integers so we'll sort them numerically using
        // the sortInt() function above
        var indexes = [];
        for (index in table)
            indexes.push (parseInt (index));
        indexes.sort (sortInt);
        
        // Use the sorted indexes we've calculated to walk through each
        // row in order
        for (var i = 0; i < indexes.length; i++) {
            // Like indexes we sort by column, so use the same trick here,
            // some rows may not have the same columns as other rows, so
            // we calculate this per row
            var columns = [];
            for (column in table[indexes[i]])
                columns.push (parseInt (column));
            columns.sort (sortInt);
            
            // Print index, then each column indented under the index
            console.log ("row for index = " + indexes[i]);
            for (var j = 0; j < columns.length; j++) {
                console.log ("   column " + columns[j] + " = "
                        + table[indexes[i]][columns[j]]);
            }
        }
    }
}

var maxRepetitions = 20;

// The maxRepetitions argument is optional, and will be ignored unless using
// SNMP verison 2c
session.tableColumns (oid, columns, maxRepetitions, responseCb);

session.trap (typeOrOid, [varbinds], [agentAddrOrOptions], callback)

The trap() method sends a SNMP trap.

The typeOrOid parameter can be one of two types; one of the constants defined in the snmp.TrapType object (excluding the snmp.TrapType.EnterpriseSpecific constant), or an OID string.

For SNMP version 1 when a constant is specified the following fields are set in the trap:

• The enterprise field is set to the OID 1.3.6.1.4.1
• The generic-trap field is set to the constant specified
• The specific-trap field is set to 0

When an OID string is specified the following fields are set in the trap:

• The final decimal is stripped from the OID string and set in the specific-trap field
• The remaining OID string is set in the enterprise field
• The generic-trap field is set to the constant snmp.TrapType.EnterpriseSpecific

In both cases the time-stamp field in the trap PDU is set to the value returned by the process.uptime () function multiplied by 100.

SNMP version 2c messages are quite different in comparison with version 1. The version 2c trap has a much simpler format, simply a sequence of varbinds. The first varbind to be placed in the trap message will be for the sysUptime.0 OID (1.3.6.1.6.3.1.1.4.1.0). The value for this varbind will be the value returned by the process.uptime () function multiplied by 100 (this can be overridden by providing upTime in the optional options parameter, as documented below).

This will be followed by a second varbind for the snmpTrapOID.0 OID (1.3.6.1.6.3.1.1.4.1.0). The value for this will depend on the typeOrOid parameter. If a constant is specified the trap OID for the constant will be used as supplied for the varbinds value, otherwise the OID string specified will be used as is for the value of the varbind.

The optional varbinds parameter is an array of varbinds to include in the trap, and defaults to the empty array [].

The optional agentAddrOrOptions parameter can be one of two types; one is the IP address used to populate the agent-addr field for SNMP version 1 type traps, and defaults to 127.0.0.1, or an object, and can contain the following items:

• agentAddr - IP address used to populate the agent-addr field for SNMP version 1 type traps, and defaults to 127.0.0.1
• upTime - Value of the sysUptime.0 OID (1.3.6.1.6.3.1.1.4.1.0) in the trap, defaults to the value returned by the process.uptime () function multiplied by 100

NOTE When using SNMP version 2c the agentAddr parameter is ignored if specified since version 2c trap messages do not have an agent-addr field.

The callback function is called once the trap has been sent, or an error occurred. The following arguments will be passed to the callback function:

• error - Instance of the Error class or a sub-class, or null if no error occurred

The following example sends an enterprise specific trap to a remote host using a SNMP version 1 trap, and includes the sysName (1.3.6.1.2.1.1.5.0) varbind in the trap. Before the trap is sent the agentAddr field is calculated using DNS to resolve the hostname of the local host:

var enterpriseOid = "1.3.6.1.4.1.2000.1"; // made up, but it may be valid

var varbinds = [
    {
        oid: "1.3.6.1.2.1.1.5.0",
        type: snmp.ObjectType.OctetString,
        value: "host1"
    }
];

dns.lookup (os.hostname (), function (error, agentAddress) {
    if (error) {
        console.error (error);
    } else {
        // Override sysUpTime, specfiying it as 10 seconds...
        var options = {agentAddr: agentAddress, upTime: 1000};
        session.trap (enterpriseOid, varbinds, agentAddress,
                function (error) {
            if (error)
                console.error (error);
        });
    }
});

The following example sends a generic link-down trap to a remote host using a SNMP version 1 trap, it does not include any varbinds or specify the agentAddr parameter:

session.trap (snmp.TrapType.LinkDown, function (error) {
    if (error)
        console.error (error);
});

The following example sends an enterprise specific trap to a remote host using a SNMP version 2c trap, and includes two enterprise specific varbinds:

var trapOid = "1.3.6.1.4.1.2000.1";

var varbinds = [
    {
        oid: "1.3.6.1.4.1.2000.2",
        type: snmp.ObjectType.OctetString,
        value: "Hardware health status changed"
    },
    {
        oid: "1.3.6.1.4.1.2000.3",
        type: snmp.ObjectType.OctetString,
        value: "status-error"
    }
];

// version 2c should have been specified when creating the session
session.trap (trapOid, varbinds, function (error) {
    if (error)
        console.error (error);
});

session.walk (oid, [maxRepetitions], feedCallback, doneCallback)

The walk() method fetches the value for all OIDs lexicographically following a specified OID in the MIB tree.

For SNMP version 1 repeated get() calls are made until the end of the MIB tree is reached. For SNMP version 2c repeated getBulk() calls are made until the end of the MIB tree is reached.

The oid parameter is an OID string. The optional maxRepetitions parameter is passed to getBulk() requests when SNMP version 2c is being used.

This method will not call a single callback once all OID values are fetched. Instead the feedCallback function will be called each time a response is received from the remote host. The following arguments will be passed to the feedCallback function:

• varbinds - Array of varbinds, and will contain at least one varbind

Each varbind must be checked for an error condition using the snmp.isVarbindError() function when using SNMP version 2c.

Once the end of the MIB tree has been reached, or an error has occurred, the doneCallback function will be called. The following arguments will be passed to the doneCallback function:

• error - Instance of the Error class or a sub-class, or null if no error occurred

Once the doneCallback function has been called the request is complete and the feedCallback function will no longer be called.

If the feedCallback function returns a true value when called no more get() or getBulk() method calls will be made and the doneCallback will be called.

The following example walks to the end of the MIB tree starting from the ifTable (1.3.6.1.2.1.2.2) OID:

var oid = "1.3.6.1.2.1.2.2";

function doneCb (error) {
    if (error)
        console.error (error.toString ());
}

function feedCb (varbinds) {
    for (var i = 0; i < varbinds.length; i++) {
        if (snmp.isVarbindError (varbinds[i]))
            console.error (snmp.varbindError (varbinds[i]));
        else
            console.log (varbinds[i].oid + "|" + varbinds[i].value);
    }
}

var maxRepetitions = 20;

// The maxRepetitions argument is optional, and will be ignored unless using
// SNMP verison 2c
session.walk (oid, maxRepetitions, feedCb, doneCb);

Example Programs

Example programs are included under the modules example directory.

Bugs & Known Issues

None, yet!

Bug reports should be sent to [email protected].

Changes

Version 1.0.0 - 14/01/2013

• Initial release including only SNMP version 1 support

Version 1.1.0 - 20/01/2013

• Implement SNMP version 2c support

Version 1.1.1 - 21/01/2013

• Correct name used in example require() call to include this module

Version 1.1.2 - 22/01/2013

• Implement subtree(), table() and walk() methods
• Support IPv6 (added transport option to the createSession() function)
• Re-order some methods in README.md

Version 1.1.3 - 27/01/2013

• Fix some typos and grammar errors in README.md
• Example snmp-table program had snmp-subtree in its usage message
• Implement example snmp-tail program to constantly poll for an OIDs value
• Add note to README.md about the ability to stop the walk() and subtree() methods by returning true

Version 1.1.4 - 29/01/2013

• Fix incorrect usage of the term "NPM" in README.md, should be "npm"

Version 1.1.5 - 05/02/2013

• The transport option to createSession() was not used

Version 1.1.6 - 12/04/2013

• Implement tableColumns() method
• Added example program snmp-table-columns.js
• Correct name of the table parameter to the table() callback
• Slight OID comparison performance enhancement

Version 1.1.7 - 11/05/2013

• Use MIT license instead of GPL

Version 1.1.8 - 22/06/2013

• Added the example program cisco-device-inventory.js
• Receive Trap failed: TypeError: value is out of bounds when sending traps using SNMP version 2c

Version 1.1.9 - 03/11/2013

• Corrected a few instances of the parameter named requestCallback to some methods in the README.md file which should have been feedCallback
• Null type is used for varbinds with a 0 value
• Correct instances of snmp.Type to snmp.ObjectType in the README.md file

Version 1.1.10 - 01/12/2013

• Error handler in the dgram.send() callback in the send() method was creating a new instance of the Error class from the error parameter, but it was already an instance of the Error class (thanks Ray Solomon)
• Add stack traces to Error classes exported by this module (thanks Ray Solomon)
• Allow users to specify 0 retries when creating a session (thanks Ray Solomon)
• Update the list of SNMP version 1 related RFCs we adhere to in the Standards Compliance section of the README.md file

Version 1.1.11 - 27/12/2013

• Add sourceAddress and sourcePort optional options to the Session classes createSession() method, which can be used to control from which IP address and port messages should be sent
• Allow users to specify sysUpTime for SNMP traps and informs

Version 1.1.12 - 02/04/2014

• The agentAddr attribute is not used when passed in the options object to the trap() method

Version 1.1.13 - 12/08/2014

• Not catching error events for the UDP socket returned from the dgram.createSocket() function
• Some request methods do not copy arguments which results in sometimes unexpected behaviour
• Use a single UDP socket for all requests in a single SNMP session
• Use a try/catch block in the timer callback in the Session.send() method
• The Session can now emit an error event to catch errors in a sessions underlying UDP socket
• The Session can now emit a close event to catch close events from a sessions underlying UDP socket, which results in the cancellation of all outstanding requests
• Added a close() method to Session to close a sessions underlying UDP socket, which results a close event
• Signed integers are treated as unsigned integers when parsing response messages

Version 1.1.14 - 22/09/2015

• Host repository on GitHub

Version 1.1.15 - 08/02/2016

• When parsing an invalid response an exception in message parsing does not interupt response processing
• Incorrectly passing req object in call to req.responseCb when handling errors during response processing

Version 1.1.16 - 29/02/2016

• Address a number of issues detected with the Mocha test suite by a user

Version 1.1.17 - 21/03/2016

• Correct reference to non-existant req variable in the Session objects constructor (should be this)

Version 1.1.18 - 15/05/2015

• Correct argument number and names to the snmp.createSession() function
• Add missing braces to an example in the README.md file

Roadmap

In no particular order:

• Use a single UDP socket for multiple sessions?
• SNMP agent (i.e. server)
• SNMP trap/inform receiver
• SNMP version 3

Suggestions and requirements should be sent to [email protected].

License

Copyright (c) 2013 Stephen Vickers

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Author

Stephen Vickers [email protected]