Difference between revisions of "TUT:mib2c General Overview"

Latest revision as of 13:18, 19 April 2012

This brief tutorial presents an overview of generating skeleton C code for a SNMP MIB using the mib2c utility.

For mib2c to work, it needs to be able to find the MIB file that defines the MIB for which it will be generating code. Running mib2c without arguments informs you of this:

 You didn't give mib2c a valid OID to start with.  IE, I could not find
 any information about the mib node "".  This could be caused
 because you supplied an incorrectly node, or by the MIB that you're
 trying to generate code from isn't loaded.  To make sure your mib is
 loaded, run mib2c using this as an example:
 
    env MIBS="+MY-PERSONAL-MIB" mib2c
 
 You might wish to start by reading the MIB loading tutorial at:
      
 http://www.net-snmp.org/wiki/index.php/TUT:Using_and_loading_MIBS
 
 And making sure you can get snmptranslate to display information about
 your MIB node.  Once snmptranslate works, then come back and try mib2c
 again.

So, if you are interested in generating code for your table XYZTable, make sure that

 snmptranslate -IR XYZTable

works first.

When you run mib2c, you must specify a MIB node for it to process. You can also specify which configuration file you would like it to use to generate the code. The available options are:

 mib2c.array-user.conf 
 mib2c.create-dataset.conf 
 mib2c.int_watch.conf
 mib2c.iterate.conf 
 mib2c.iterate_access.conf 
 mib2c.mfd.conf 
 mib2c.notify.conf 
 mib2c.old-api.conf 
 mib2c.scalar.conf

Running mib2c without specifying a configuration file will prompt you with some questions to help determine which one might be appropriate for your situation.

One thing many people get confuse about is what to do after running mib2c. Contrary to popular belief, simply running mib2c on a MIB does not generate a complete implementation for the module, as indicated by this warning printed after running mib2c without specifying a configuration file:

 **********************************************************************
 * NOTE WELL: The code generated by mib2c is only a template.  *YOU*  *
 * must fill in the code before it'll work most of the time.  In many *
 * cases, spots that MUST be edited within the files are marked with  *
 * /* XXX */ or /* TODO */ comments.                                  *
 **********************************************************************

So once you've generated the template (aka skeleton) code for your mib, you need to edit the code and implement the portions of the code specific to your module. As more elaborate configuration files are developed, it should become simpler to identify the what/when/where portions of the code (the MFD configuration file is the latest step towards this goal - see the MFD tutorial here).

The next section covers the shell script mib2c-update, which is a wrapper around mib2c to help you take advantage of updates to the configuration file you chose for your mib module.

Tutorial Sections

About the SNMP Protocol

These tutorial links talk about SNMP generically and how the protocol itself works. They are good introductory reading material and the concepts are important to understand before diving into the later tutorials about Net-SNMP itself.

• How SNMP Works: About the protocol itself (GETs, GETNEXTs, etc)
• What data is in SNMP: All about SNMP Management Information Bases (MIBs)
• Securing SNMP: How to use the SNMP protocol securely

Net-SNMP Command Line Applications

These tutorial pages discuss the command line tools provided in the Net-SNMP suite of tools. Nearly all the example commands in these tutorials works if you try it yourself, as they're all examples that talk to our online Net-SNMP test agent. Given them a shot!

• snmptranslate: learning about the MIB tree.
• snmpget: retrieving data from a host.
• snmpgetnext: retrieving unknown indexed data.
• snmpwalk: retrieving lots of data at once!
• snmptable: displaying a table.
• snmpset: peforming write operations.
• snmpbulkget: communicates with a network entity using SNMP GETBULK request
• snmpbulkwalk: retrieve a sub-tree of management values using SNMP GETBULK requests.
• snmptrap: Sending and receiving traps, and acting upon them.
  • Traps/informs with SNMPv3/USM: Sending and receiving SNMPv3/USM TRAPs and INFORMs
  • Sending Traps/Informs via AgentX: Sending notifications from the command line through snmpd
• Common command line options:
  • Using and loading MIBS
  • SNMPv3/USM Options
  • Using SNMPv3 over TLS and DTLS
  • Customized Output Formats
• Writing mib2c config files

Application Configuration

All of our applications support configuration to allow you to customize how they behave.

• Configuration files for Net-SNMP applications

Net-SNMP Daemons

Net-SNMP comes with two long-running daemons: a SNMP agent (snmpd) for responding to management requests and a notification receiver (snmptrapd) for receiving SNMP notifications.

• SNMP Agent (snmpd) Configuration
  • Configuration Basics
  • Access Control (VACM)
  • snmpconf
• SNMP Notification Receiver (snmptrapd)
  • Configuring snmptrapd
  • Configuring SNMPv3 notifications
  • Configuring snmptrapd to understand vendor-specific MIBS (Cisco)
• Agent Monitoring
  • DisMan Monitoring
  • Monitoring with MRTG

Coding Tutorials

Net-SNMP comes with a highly flexible and extensible API. The API allows you to create your own commands, add extensions to the agent to support your own MIBs and perform specialized processing of notifications.

• Client / Manager Coding Tutorials
  • Writing a simple application
  • Writing a simple asynchronous application
• Agent Coding Tutorials
  • The Agent Architecture page might be worth reading before or after the agent coding tutorials, and describes how the Agent Helpers work under the hood.
  • Writing a mib module to serve information described by an SNMP MIB, and how to compile it into the net-snmp snmpd agent.
  • Writing a Dynamically Loadable Object that can be loaded into the SNMP agent.
  • Writing a Subagent that can be run to attach to the snmpd master agent.
  • Writing a perl plugin to extend the agent using the NetSNMP::agent module.
  • Writing shell scripts to extend the agent
  • Using mib2c to help write an agent code template for you
    • General mib2c Overview
    • Using the mib2c-update script to recode your code
    • mib2c.mfd.conf tutorial
• Header files and autoconf

Debugging SNMP Applications and Agents

All our tools and applications have extensive debugging output. These tutorials talk about how the debugging system works and how you can add your own debugging statements to you code:

• Debugging output printed using the -D command line option
  • Putting DEBUGMSG tokens in your code
• Using -Ddump to display packet breakdowns
• Debugging using GDB

Operating System Specific Tutorials

• Building With Visual Studio 2005 Express
  • Using the command line and nmake
• Building Net-SNMP 64-bit with Visual C++ 2010 Express
  • Using the command line and nmake (VC++ 2010 Express)
• Net-Snmp on Ubuntu
• Net-SNMP and lm-sensors on Ubuntu 10.04
• Net-SNMP for windows:
  • How to install: [1]
  • How to configure: [2]