PySMI: SNMP MIB Parser and Converter

1.6.3 · active · verified Sat Apr 11

PySMI is a pure-Python implementation of an SNMP SMI MIB parser and conversion library. It takes ASN.1 MIBs and can transform them into various formats, including JSON documents and PySNMP-compatible Python modules. It understands SMIv1, SMIv2, and common de-facto SMI dialects, and can automatically pull MIBs from local directories, ZIP archives, and HTTP servers. The current version is 1.6.3 and it actively supports Python 3.9+.

Warnings

gotcha By default, PySMI does not include MIB descriptions, comments, or references in the generated output (e.g., JSON or PySNMP modules) to minimize size. This can lead to a less verbose output than expected.
Fix: Pass `genTexts=True` to the `MibCompiler.compile()` method to include full textual descriptions and references from the MIB.
gotcha PySMI performs caching and will not recompile a MIB if a 'fresh enough' version already exists in its search paths. This can be unexpected during development or when changes are made to source MIBs.
Fix: To force unconditional recompilation, pass `rebuild=True` to the `MibCompiler.compile()` method. For parser lookup tables, configure a cache directory using `--cache-directory` option (if using `mibdump.py`) or similar API for performance.
gotcha Some foundational MIBs (e.g., SNMPv2-SMI, SNMPv2-TC, RFC-1212) contain base SMI types or ASN.1 MACRO definitions that should generally not be transformed by PySMI. Attempting to compile these can lead to errors or incorrect output.
Fix: Explicitly 'blacklist' such MIBs using `StubSearcher` in your `MibCompiler` configuration. `PySnmpCodeGen.baseMibs` provides a pre-defined list for PySNMP target generation. For example: `mibCompiler.addSearchers(StubSearcher(*PySnmpCodeGen.baseMibs))`.
gotcha Poorly formed or 'broken' ASN.1 MIBs are common in practice and can cause parsing failures. While PySMI attempts workarounds, severely broken MIBs may not compile.
Fix: Utilize PySMI's 'borrow' feature by configuring a source for pre-compiled MIBs. This allows PySMI to fetch already transformed MIBs if the source ASN.1 MIB cannot be found or parsed. Example: `mibCompiler.addSearchers(PyFileSearcher('/path/to/precompiled/mibs'))` or an `HttpReader` to `mibs.snmplabs.com`.

Install

pip install pysmi Install PySMI

Imports

MibCompiler
```
from pysmi.compiler import MibCompiler
```

SmiV2Parser

from pysmi.parser.smi import SmiV2Parser

JsonCodeGen

from pysmi.codegen.json import JsonCodeGen

PySnmpCodeGen

from pysmi.codegen.pysnmp import PySnmpCodeGen

FileReader

from pysmi.reader.localfile import FileReader

CallbackWriter

from pysmi.writer.callback import CallbackWriter

Quickstart

This quickstart demonstrates how to compile an in-memory ASN.1 MIB module (`FOO-MIB`) into a JSON document using PySMI's `MibCompiler`. It sets up a `CallbackReader` to supply the MIB content and a `CallbackWriter` to print the resulting JSON to the console, illustrating the core transformation process.

import os
from pysmi.compiler import MibCompiler
from pysmi.parser.smi import SmiV2Parser
from pysmi.codegen.json import JsonCodeGen
from pysmi.reader.callback import CallbackReader
from pysmi.writer.callback import CallbackWriter

# Example MIB content (simplified for demonstration)
mib_content = """
FOO-MIB DEFINITIONS ::= BEGIN
  IMPORTS
    MODULE-IDENTITY, OBJECT-TYPE, enterprises
      FROM SNMPv2-SMI;

  fooModule MODULE-IDENTITY
    LAST-UPDATED "202301010000Z"
    ORGANIZATION "Example Corp"
    CONTACT-INFO "support@example.com"
    DESCRIPTION
      "The MIB module for example devices."
    REVISION "202301010000Z"
    DESCRIPTION "Initial revision."
    ::= { enterprises 99999 }

  fooObjects OBJECT IDENTIFIER ::= { fooModule 1 }

  fooStatus OBJECT-TYPE
    SYNTAX INTEGER { up(1), down(2) }
    MAX-ACCESS read-only
    STATUS current
    DESCRIPTION
      "The operational status of a foo device."
    ::= { fooObjects 1 }

END
"""

def store_json_mib(mib_name, mib_data, *args):
    print(f"--- Compiled MIB: {mib_name} ---")
    print(mib_data)

# Initialize compiler infrastructure
mibCompiler = MibCompiler(
    SmiV2Parser(),
    JsonCodeGen(),
    CallbackWriter(store_json_mib)
)

# Add a reader that can provide our MIB content by name
mibCompiler.addSources(CallbackReader(lambda mibName, **kwargs: mib_content if mibName == 'FOO-MIB' else None))

# Compile the MIB
# Note: 'rebuild=True' forces compilation even if cached, 'genTexts=True' includes MIB descriptions
results = mibCompiler.compile('FOO-MIB', rebuild=True, genTexts=True)

print(f"Compilation results: {results}")

view raw JSON →