opn_arp_table

THE RISK

Low Risk

Why opn_arp_table needs a policy

This tool retrieves and displays ARP (Address Resolution Protocol) table data—IP-to-MAC address mappings—which is a read-only diagnostic query. It has no side effects, does not modify system state, does not execute code, and poses minimal risk. The 'Get' verb in the description confirms query semantics.

From the tool's definition Tool name 'opn_arp_table' combined with description 'Get the ARP table showing IP-to-MAC address mappings' indicates a retrieval operation that queries existing network state without modification.

Documented attack patterns abuse exactly the kind of access opn_arp_table gives an agent:

POLICY

How to control opn_arp_table

PolicyLayer is an MCP gateway — it sits between your AI agents and OPNsense MCP Server, and nothing reaches the server without passing your rules. This is the rule we recommend for opn_arp_table:

policy.json

{
  "version": "1",
  "default": "deny",
  "tools": {
    "opn_arp_table": {}
  }
}

opn_arp_table is read-only, so it stays allowed — but everything else on the server is denied unless you say otherwise.

Create a free account and register OPNsense MCP Server — nothing to install.
Add this policy — paste it, or build it visually.
Point your MCP client (Claude, Cursor, anything) at your gateway URL.

CAP THIS TOOL →

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EXPLORE

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Go deeper

The MCP Attack Database → Documented attack patterns against MCP deployments — and the policies that stop them.
Data exfiltration → How read access becomes an exfiltration channel when chained with untrusted content.
MCP token cost → What connecting this server costs in context-window tokens on every request.
Rate Limiting MCP Tool Calls: A Practical Guide →
MCP Security: Why Prompt Guardrails Aren't Enough →

FAQ

Questions about opn_arp_table

What does the opn_arp_table tool do? +

Get the ARP table showing IP-to-MAC address mappings. It is categorised as a Read tool in the OPNsense MCP Server MCP Server, which means it retrieves data without modifying state.

How do I enforce a policy on opn_arp_table? +

Register the OPNsense MCP Server MCP server in PolicyLayer and add a rule for opn_arp_table: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches OPNsense MCP Server. Nothing to install.

What risk level is opn_arp_table? +

opn_arp_table is a Read tool with low risk. Read-only tools are generally safe to allow by default.

Can I rate-limit opn_arp_table? +

Yes. Add a rate_limit block to the opn_arp_table rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.

How do I block opn_arp_table completely? +

Set action: deny in the PolicyLayer policy for opn_arp_table. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.

What MCP server provides opn_arp_table? +

opn_arp_table is provided by the OPNsense MCP Server MCP server (lucamarien/opnsense-mcp-server). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.

Enforce policy on every OPNsense MCP Server tool call.

Start from OPNsense MCP Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.

CHECK YOUR STACK →