Difference between revisions of "TUT:Configuring snmptrapd to receive SNMPv3 notifications"

Revision as of 17:10, 10 October 2007

SNMPv3 background

Before you can begin to understand how to use snmptrapd with SNMPv3 protected notifications you need to understand some basic concepts. Specifically, please read:

• SNMPv3 Options -- Documents how to use Net-SNMP with SNMPv3 in general
• TUT:snmptrap -- Discussing SNMP notifications and sending them using snmptrap
• TUT:snmptrap SNMPv3 -- Discussing SNMPv3 notifications and sending them using snmptrap

SNMP INFORMs vs SNMP TRAPs Notifications

SNMP supports two types of notifications: TRAPs and INFORMs. (In SNMPv1, there was only TRAPs; SNMPv2c and SNMPv3 support INFORMs too). There is one fundamental difference between SNMP INFORMs and TRAPs:

TRAPs

Sent by an application or daemon but no response is sent or expected by the notification receiver.

INFORMs

INFORMs are nothing more than an acknowledged TRAP. I.E., when the notification receiver receives an INFORM it sends a response back that indicates "I got it". (An application may be configured to send more than one INFORM message if it failed to receive an acknowledgment)

SNMPv3 INFORMs vs SNMP TRAPs

SNMPv3 with the User-Based Security Model (USM) makes use of an EngineID identifier for the SNMPv3 application that is authoratative (meaning the one who controls the flow of information).

• With SNMPv3 TRAPs, the authoratative engine is the engine that sends the trap

• With SNMPv3 INFORMs, the authoratative engine is the engine that receives the trap.

SNMPv3 USM users are uniquely defined by a combination of the authoratative EngineID and the user name.

Configuring snmptrapd for receiving SNMPv3 TRAPs

Since the application sending the TRAP is authoratative, that means the user created within the snmptrapd must be tied to the EngineID sending the trap. You do this by creating a line like the following in your /var/net-snmp/snmptrapd.conf file:

 createUser -e ENGINEID myuser SHA "my authentication pass" AES "my encryption pass"

In the above line, the following things need to be set:

ENGINEID; the EngineID of the application that is going to be sending the trap. (see below)

myuser; the USM username that is going to be sending the trap.

SHA; the authentication type (SHA or MD5, with SHA being better)

"my authentication pass"; The authentication pass-phrase to use to generate the secret authentication key. Enclose it in quotation marks if it contains spaces.

AES; the encryption type to use (AES or DES, with AES being better)

"my encryption pass"; The encryption pass-phrase to use to generate the secret encyrption key. Enclose it in quotation marks if it contains spaces. If you leave it off, it will be set to the same pass-phrase as the authentication pass-phrase.

Authorizing your user to do things with the received notifications

Now that your user has been properly created, you still need to allow snmptrapd to do things with the traps and INFORMs that get sent. EG, just because the request has been received and (cryptographically) verified that it was authentic, snmptrapd still won't do anything with the notification if it isn't allowed to.

In your /usr/local/share/snmp/snmaptrapd.conf file put:

 authUser log,execute,net myuser

This line lets snmptrapd receive traps authenticated with the myuser passwords log, execute commands and forward them. (By default, snmptrapd only logs received notifications but it can be setup to execute commands and to forward notifications to somewhere else). The snmptrapd.conf manual page describes this configuration directive in greater detail. Please refer to it for details. for the other options that are available.

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]