如何让Snmp tran input plugin的Community接受所有字符串？

Hey there! Let's break down how to remove the community string restriction for your SNMP Trap Input plugin—right now it only lets you specify a single string or array of strings, defaulting to public when nothing's set. Here are two reliable approaches:

1. Modify the Plugin's Community Validation Logic (Root Fix) #

This is the most straightforward way to eliminate the restriction entirely, since it targets the core check that blocks unconfigured community strings.

First, locate the plugin's core code file. For example, if you're using the Logstash SNMP Trap plugin, you'll find it at something like logstash-input-snmp/lib/logstash/inputs/snmp.rb.

Next, find the section where the plugin validates the incoming community string. It’ll look something like this (simplified example):

# Original validation logic
if @communities.include?(community)
  # Process the trap normally
else
  logger.warn("Rejecting trap with invalid community", community: community)
  return
end

To accept any community string, you can either:

• Remove the validation check entirely: Delete or comment out the if/else block, so the trap processing runs no matter what the community string is.
• Replace with a catch-all condition: If you want to keep a placeholder for future tweaks, change the check to always evaluate to true, like:

  # Modified logic to accept any community
  if true # Skip validation
    # Process the trap normally
  end
  

After making the change, recompile/reload the plugin (if needed) and restart your service (e.g., Logstash). Just keep in mind: if you update the plugin later, your changes will be overwritten—so consider forking the plugin repo to maintain your custom version, or submit a feature request to the official project if this is a use case others might need.

2. Configuration Workaround (No Code Changes) #

If you don’t want to mess with plugin code, check if your version of the SNMP Trap Input plugin supports regular expressions for community strings. If it does, you can set a regex that matches any string:

Here’s an example configuration (using Logstash YAML syntax):

input {
  snmp {
    traps => {
      community => /.*/ # Regex to match any character sequence
    }
  }
}

Heads up: Not all plugin versions support regex for community strings—this depends on how the plugin was built. If your plugin only accepts fixed strings or arrays, this workaround won’t work, and you’ll need to go with the code modification approach.

Important Security Note #

Removing community string validation means any device on your network can send SNMP traps to your service, which could open you up to unwanted traffic or malicious activity. Make sure to pair this change with other security controls, like IP whitelisting for allowed trap senders, to keep your setup secure.

内容的提问来源于stack exchange，提问作者Sunil Hiray