AI agents use opn_add_nat_rule to create or update resources in OPNsense MCP Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your OPNsense MCP Server environment.
The 'add' prefix consistently indicates creation/write operations across sibling tools (opn_add_alias, opn_add_firewall_rule, etc.). Adding a NAT rule modifies firewall network address translation configuration, which is reversible but high-severity as misconfiguration can expose internal services or disrupt network traffic. Description is empty, lowering confidence slightly.
From the tool's definition Tool name 'opn_add_nat_rule' — 'add' suggests creation of a new NAT rule on an OPNsense firewall.
Documented attack patterns abuse exactly the kind of access opn_add_nat_rule gives an agent:
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_add_nat_rule:
{
"version": "1",
"default": "deny",
"tools": {
"opn_add_nat_rule": {
"limits": [
{
"counter": "opn_add_nat_rule_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}opn_add_nat_rule stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
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opn_add_nat_rule. It is categorised as a Write tool in the OPNsense MCP Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the OPNsense MCP Server MCP server in PolicyLayer and add a rule for opn_add_nat_rule: 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.
opn_add_nat_rule is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the opn_add_nat_rule 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.
Set action: deny in the PolicyLayer policy for opn_add_nat_rule. 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.
opn_add_nat_rule 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.
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.
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81 OPNsense MCP Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.