Python3 AgentX Implementation

PyAgentX3 is a pure Python3 implementation of the AgentX protocol (RFC 2741), it will allow to extend an SNMP agent (e.g snmpd) by writing AgentX subagents, without modifying the original SNMP agent.

RFC 2741: Agent Extensibility (AgentX) Protocol

This is a fork of the Python2 based PyAgentX package (available at https://github.com/hosthvo/pyagentx) modified for Python3 and enhanced (e.g. SNMP traps).

Features

Currently the code is capable of the following:

• Open a session with AgentX master, e.g. net-snmpd snmpd, and register a new session.
• Send Ping request.
• Register multiple MIB regions.
• Multiple MIB update classes with custom frequency for each.
• Support snmpset operations.
• Reconnect/Retry to master, in case the master restarted.
• Support for SNMPv2 traps.

Prerequisites

A running and correctly configured SNMP daemon (e.g. net-snmp) is required. Install using your OS package manager or from source. For Ubuntu for example use:

apt install snmpd snmptrapd snmp-mibs-downloader

Note: For some licensing reasons snmp-mibs-downloader can only be downloaded after enabling non-free software on some distributions. For Debian enable non-free for Ubuntu multiverse.

# for Ubuntu
apt install software-properties-common
add-apt-repository multiverse
apt install snmp-mibs-downloader

Installation

The package is registered on Python Package Index under the name "pyagentx3" https://pypi.python.org/pypi/pyagentx3.

You can install it by simply running:

pip install pyagentx3

SNMP Agent Configuration

You need to make sure the SNMP agent snmpd will act as AgentX master:

master          agentx

Also make sure the SNMP agent accept requests for the wanted MIB region:

# NET-SNMP-EXAMPLES-MIB
view   systemview  included   .1.3.6.1.4.1.8072.2

NOTE: You need to change the OID to reflect your own OID.

Minimal Agent

To implement an agent you need to provide one "Agent" class and one or more "Updater" classes. A simple agent might look like:

import pyagentx3

# Updater class that set OID values
class NetSnmpPlaypen(pyagentx3.Updater):
    def update(self):
        self.set_INTEGER('1.0', 1000)
        self.set_OCTETSTRING('3.0', 'String for NET-SNMP-EXAMPLES-MIB')

class MyAgent(pyagentx3.Agent):
    def setup(self):
        # Register Updater class that responsd to
        # the tree under "netSnmpPlaypen": 1.3.6.1.4.1.8072.9999.9999
        self.register('1.3.6.1.4.1.8072.9999.9999', NetSnmpPlaypen)

# Main
pyagentx3.setup_logging()
try:
    a = MyAgent()
    a.start()
except Exception as e:
    print "Unhandled exception:", e
    a.stop()
except KeyboardInterrupt:
    a.stop()

To test:

snmpwalk -v 2c -c public localhost NET-SNMP-MIB::netSnmpPlaypen

Example agent and scripts

To test the implementation the samples directory contains a sample agent that implements some parts of NET-SNMP-EXAMPLES-MIB including a tables and traps.

Also in this directory some sample scripts exists which allow to query and set OID's.

FAQ

What OID should I use for my agent?

If you are just playing and experminting you can put everything under NET-SNMP-MIB::netSnmpPlaypen OID 1.3.6.1.4.1.8072.9999.9999 tree, but you shouldn't use it for any public work.

If you need to publish your work you should apply for your own enterprise OID on the IANA PEN Application page, this will give you your own private tree, e.g. Net-Snmp uses 1.3.6.1.4.1.8072, Google uses 1.3.6.1.4.1.11129

So your company would have an OID 1.3.6.1.4.1.xxxxx

You also need to write your own MIB to allow your customer to use in thier Network Managment System (NMS):

http://www.net-snmp.org/wiki/index.php/Writing_your_own_MIBs

Are there other ways to extend SNMP agent?

Some SNMP agents can be extended using different mechanisms, e.g. net-snmp can be extended using:

• running external commands (exec, extend, pass)
• loading new code dynamically (embedded perl, dlmod)
• communicating with other agents (proxy, SMUX, AgentX)

Check "EXTENDING AGENT FUNCTIONALITY" in snmpd.conf man page for more details.

What's the difference between AgentX, SMUX and proxied SNMP?

Check the answer here

What is advatages of extending SNMP using AgentX instead of something like "pass_perssist"?

One advantage is to decouple the master SNMP agent from its sub-agents, which means you can start/stop one without affecting the other, and you don't have to change the snmpd.conf every time you want to add or remove a sub-agent.

Another advantage is the support for traps in AgentX.

Why do I need sudo to run my AgentX agent?

By default snmpd uses UNIX socket to communicate with AgentX sub-agents, it uses special permisssions to prevent unauthorized agents.

If you don't want to use root to run the agent you can use agentXPerms directive in snmpd.conf, check the man page for its options.

My agent connected to the master but I couldn't get any results with snmpwalk?

First make sure you can get results from the agent, try something basic:

snmpwalk -v 2c -c public localhost .

If the command doesn't return anything, double check your agent community and Access List.

If it works on standard OIDs but it doesn't work on your sub-agent, make sure you include the correct OID view:

view   systemview  included   .1.3.6.1.4.1.8072.2

How can I test it on Mac OSX?

SNMP agent from net-snmp is already installed on OSX, but first you need to load it:

sudo launchctl load -w /System/Library/LaunchDaemons/org.net-snmp.snmpd.plist

Then you can start and stop it with these commands:

sudo launchctl start org.net-snmp.snmpd
sudo launchctl start org.net-snmp.snmpd

The configuration file can be found on the default location /etc/snmp/snmpd.conf.