net-snmp Creating my own MIB: No Such Instance currently exists at this OID [closed]

Question

First thing first. I want to create my own MIB.

Please pardon me if I'm asking a simple question as I'm a newbie to SNMP and I'm struggling on this from couple of weeks. I have already been through TUT:mib2c.

UPDATE: I've the following MIB named SAMPLE-MIB, which compiles good without any error (This compilation is done only on the agent system, not on the server).

SAMPLE-MIB DEFINITIONS ::= BEGIN

IMPORTS
    MODULE-IDENTITY, OBJECT-TYPE, Integer32,
        NOTIFICATION-TYPE                       FROM SNMPv2-SMI
        SnmpAdminString                         FROM SNMP-FRAMEWORK-MIB
        netSnmp                                 FROM NET-SNMP-MIB
;



sample    MODULE-IDENTITY
    LAST-UPDATED "201709120200Z"
    ORGANIZATION "NCS"
    CONTACT-INFO
        "@ncs-in.com"        
    DESCRIPTION
        "A test MIB"
    REVISION    "201709120200Z"
    DESCRIPTION
        "initial Draft"
    ::= { iso org(3) dod(6) internet(1) private(4) enterprises(1) 39106 }

sampleResearch               OBJECT IDENTIFIER ::= { sample 2 }

sampleVar OBJECT-TYPE
    SYNTAX Integer32
    MAX-ACCESS  read-write
    STATUS  current
    DESCRIPTION
        "testing"
    ::= { sampleResearch 1}

END

I have already done this:

root@snmp-agent:# MIBS=+SAMPLE-MIB  
root@snmp-agent:# export MIBS    
root@snmp-agent:# MIBS=ALL

My MIB files are in this path: /usr/share/snmp/mibs which is the default search path. I've already compiled it and generated .c and .h files successfully, like this:

root@snmp-agent:# snmptranslate -On SAMPLE-MIB::sampleVar
root@snmp-agent:# snmptranslate -IR SAMPLE-MIB
root@snmp-agent:# mib2c -c mib2c.scalar.conf sampleVar

NOTE: These sampleVar.c and sampleVar.h files are in the path: /home/snmp-agent/Desktop/project/net-snmp-5.7.3/agent/mibgroup/.

To keep it simple I din't modify anything in the sampleVar.h and this is how my sampleVar.c file looks:

/*

 * Note: this file originally auto-generated by mib2c using

 *        $

 */



#include <net-snmp/net-snmp-config.h>

#include <net-snmp/net-snmp-includes.h>

#include <net-snmp/agent/net-snmp-agent-includes.h>

#include "sampleVar.h"







static int myvar=10;

/** Initializes the sampleVar module */

void

init_sampleVar(void)

{

    const oid sampleVar_oid[] = { 1,3,6,1,4,1,39106,2,1 };

    const size_t sampleVar_oid_len   = OID_LENGTH(sampleVar_oid);

    netsnmp_handler_registration    *reg;

    netsnmp_iterator_info           *iinfo;

    netsnmp_table_registration_info *table_info;



  DEBUGMSGTL(("sampleVar", "Initializing\n"));



   /* netsnmp_register_scalar(

        netsnmp_create_handler_registration("sampleVar", handle_sampleVar,

                               sampleVar_oid, OID_LENGTH(sampleVar_oid),

                               &,HANDLER_CAN_RWRITE   ));*/



 netsnmp_register_int_instance("sampleVar",

                                  sampleVar_oid,

                                  OID_LENGTH(sampleVar_oid),

                                  &myvar, NULL);





}



int

handle_sampleVar(netsnmp_mib_handler *handler,

                          netsnmp_handler_registration *reginfo,

                          netsnmp_agent_request_info   *reqinfo,

                          netsnmp_request_info         *requests)

{

    int ret = 120892;

    netsnmp_request_info       *request;

    netsnmp_table_request_info *table_info;

    struct poolTable_entry          *table_entry;

    /* We are never called for a GETNEXT if it's registered as a

       "instance", as it's "magically" handled for us.  */



    DEBUGMSGTL(("sampleVar", "Initializing\n"));



    /* a instance handler also only hands us one request at a time, so

       we don't need to loop over a list of requests; we'll only get one. */







    return ret;

}

Now I reconfigure net-snmp with the MIB's like this:

./configure --with-mib-modules="sampleVar"
make
make install

After this when I do (on the agent) snmptranslate -IR sampleVar.0 I get the output as:

root@snmp-agent:# snmptranslate -IR sampleVar.0
SAMPLE-MIB::sampleVar.0 (expected output of the command)

And with the command snmptranslate -On objectName.0 I get output as:

root@snmp-agent:# snmptranslate -On SAMPLE-MIB::sampleVar.0
.1.3.6.1.4.1.39106.2.1 (expected output of the command)

When I do snmpwalk on server:

snmp-server:# snmpwalk -v 2c -c ncs -m SAMPLE-MIB 192.168.5.22 .1.3.6.1.4.1.39106.2.1
SAMPLE-MIB::sampleVar.2.18.46.49.46.51.46.54.46.49.46.52.46.49.46.51.57.49.48.54 = Wrong Type (should be INTEGER): STRING: "/bin/echo"
SAMPLE-MIB::sampleVar.3.18.46.49.46.51.46.54.46.49.46.52.46.49.46.51.57.49.48.54 = Wrong Type (should be INTEGER): ""
SAMPLE-MIB::sampleVar.4.18.46.49.46.51.46.54.46.49.46.52.46.49.46.51.57.49.48.54 = Wrong Type (should be INTEGER): ""
SAMPLE-MIB::sampleVar.5.18.46.49.46.51.46.54.46.49.46.52.46.49.46.51.57.49.48.54 = INTEGER: 5
SAMPLE-MIB::sampleVar.6.18.46.49.46.51.46.54.46.49.46.52.46.49.46.51.57.49.48.54 = INTEGER: 1
SAMPLE-MIB::sampleVar.7.18.46.49.46.51.46.54.46.49.46.52.46.49.46.51.57.49.48.54 = INTEGER: 1
SAMPLE-MIB::sampleVar.20.18.46.49.46.51.46.54.46.49.46.52.46.49.46.51.57.49.48.54 = INTEGER: 4
SAMPLE-MIB::sampleVar.21.18.46.49.46.51.46.54.46.49.46.52.46.49.46.51.57.49.48.54 = INTEGER: 1

But, When I do snmpget from my server, I get:

root@snmp-server:# snmpget 192.168.5.22 sampleVar.0
SAMPLE-MIB::sampleVar = No Such Object available on this agent at this OID
root@snmp-server:# snmpget -v 2c -c ncs 192.168.5.22 -m SAMPLE-MIB .1.3.6.1.4.1.39106.2.1
SAMPLE-MIB::sampleResearch.3.1.2 = No Such Object available on this agent at this OID

I do get expected output for sysUpTime.0 from my server:

root@snmp-server:# snmpget 192.168.5.22 sysUpTime.0
DISMAN-EVENT-MIB::sysUpTimeInstance = Timeticks: (721781) 2:00:17.81 (OUTPUT)

I have googled it and still searching but no luck. So anyone can tell me what to do next? How should I use snmpget from my server on my own MIBs?

Any ideas or suggestions are highly appreciated. Thank you.

UPDATE 2: Output from snmpgetnext:

root@snmp-server:~# snmpgetnext -v 2c -c ncs 192.168.5.22 -m SAMPLE-MIB .1.3.6.1.4.1.39106.2.1
SAMPLE-MIB::sampleVar.2.18.46.49.46.51.46.54.46.49.46.52.46.49.46.51.57.49.48.54 = Wrong Type (should be INTEGER): STRING: "/bin/echo"
root@snmp-server:~# snmpgetnext -v 2c -c ncs 192.168.5.22 -m SAMPLE-MIB .1.3.6.1.4.1.39106.2.2
SAMPLE-MIB::sample.3.1.1.18.46.49.46.51.46.54.46.49.46.52.46.49.46.51.57.49.48.54 = ""

As you said: snmpget is used to target a specific OID in SNMP, So accordingly when I specify the complete OID, I get correct output:

root@snmp-server:~# snmpget -v 2c -c ncs -m SAMPLE-MIB 192.168.5.22 sampleVar.2.18.46.49.46.51.46.54.46.49.46.52.46.49.46.51.57.49.48.54
SAMPLE-MIB::sampleVar.2.18.46.49.46.51.46.54.46.49.46.52.46.49.46.51.57.49.48.54 = Wrong Type (should be INTEGER): STRING: "/bin/echo"

But what is this: sampleVar.2.18.46.49.46.51.46.54.46.49.46.52.46.49.46.51.57.49.48.54? What's wrong here? I don't understand that! I din't specify this stuff!!!!

Answer 1

I think your issue is coming from a simple misconception of how SNMP data (OIDs) is structured, and how snmpwalk, snmpget, and snmpgetnext interact with it.

SNMP organizes the OIDs into related nested trees (or tables), the MIBs define those trees and the OIDs in them.

It's important to understand how snmpget and snmpgetnext works before getting into snmpwalk

1. snmpget

snmpget is used to target a specific OID in SNMP. This assumes I know the exact OID I want data from, for example, I want the first entry in the IF-MIB::ifName table (1.3.6.1.2.1.31.1.1.1.1.1.1). I know that the entry is there for a fact, so it will return a value.

[jhead@sonder ~]$ snmpget -On -v2c -c public 1.2.3.4 1.3.6.1.2.1.31.1.1.1.1.1
.1.3.6.1.2.1.31.1.1.1.1.1 = STRING: fxp0

2. snmpgetnext

snmpgetnext is for when you don't know exactly how things are organized on your target system. Meaning, you know that system has the IF-MIB::ifName table, but you don't know exactly what the first entry is. snmpgetnext's job is to literally find, the next entry to whatever OID you point it at.

I know for a fact that 1.3.6.1.2.1.31.1.1.1.1.2 does not exist on my target system, lets verify that with an snmpget:

[jhead@sonder ~]$ snmpget -On -v2c -c public 1.2.3.4 1.3.6.1.2.1.31.1.1.1.1.2
.1.3.6.1.2.1.31.1.1.1.1.2 = No Such Instance currently exists at this OID

Now let's try an snmpgetnext:

[jhead@sonder ~]$ snmpgetnext -On -v2c -c public 1.2.3.4 1.3.6.1.2.1.31.1.1.1.1.2
.1.3.6.1.2.1.31.1.1.1.1.4 = STRING: lsi

It looks like my next entry is .4, great!

3. snmpwalk

snmpwalk is effectively a recursive search on whatever OID value you target. snmpwalk actually executes multiple snmpgetnext operations to determine the contents of the table, because that table might vary in size, or change over time.

For example, if I wanted to retrieve all OID entries for IF-MIB::ifName (my particular MIB defines that as 1.3.6.1.2.1.31.1.1.1.1)

[jhead@sonder ~]$ snmpwalk -On -v2c -c public 1.2.3.4 1.3.6.1.2.1.31.1.1.1.1
.1.3.6.1.2.1.31.1.1.1.1.1 = STRING: fxp0
.1.3.6.1.2.1.31.1.1.1.1.4 = STRING: lsi
.1.3.6.1.2.1.31.1.1.1.1.5 = STRING: dsc
.1.3.6.1.2.1.31.1.1.1.1.6 = STRING: lo0
.1.3.6.1.2.1.31.1.1.1.1.7 = STRING: tap
.1.3.6.1.2.1.31.1.1.1.1.8 = STRING: gre
.1.3.6.1.2.1.31.1.1.1.1.9 = STRING: ipip

As you can see, I retrieved all entries in that table of OIDs.

snmpwalk will also recurse through a table A, if table A contains tables B, C, and D. Such as the entire DISMAN-PING-MIB in your example, it will recurse those as well.

4. Your original question.

Now, lets take a look at why you can't use snmpget to target a table like you did in your example:

[jhead@sonder ~]$ snmpget -On -v2c -c public 1.2.3.4 1.3.6.1.2.1.31.1.1.1.1
.1.3.6.1.2.1.31.1.1.1.1 = No Such Instance currently exists at this OID

It fails because that OID is a table, no specific information tied to .1.3.6.1.2.1.31.1.1.1.1, it is just a container for the rest of the information.

There are more than the 3 methods I mentioned, like snmpbulkwalk and others. Which method you use could vary depending upon what you're trying to accomplish, but I suspect snmpwalk will work fine. You can see examples here.