fix: _action_fix_snmp adds floating firewall rule for UDP/161

OPNsense default-drops traffic arriving on non-LAN interfaces (e.g.
WireGuard tunnels used as management networks). Even with os-net-snmp
running and configured, SNMP is unreachable from external management
hosts because no firewall rule allows it.

Now adds a floating pass rule for UDP/161 → (self) after configuring
the service, then applies the firewall. Skips the rule if one with
the same description already exists (idempotent).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

napalm_opnsense/opnsense.py

@@ -1541,24 +1541,29 @@ class OPNsenseDriver(FirewallDriver):
         raise NotImplementedError(f"Unknown action: {action!r}")
 
     def _action_fix_snmp(self) -> dict[str, Any]:
-        """Install os-net-snmp plugin, configure community 'public', start service.
+        """Install os-net-snmp plugin, configure community 'public', open firewall.
 
         Steps:
-        1. Install os-net-snmp via firmware API (idempotent — no-op if installed)
+        1. Install os-net-snmp via firmware API (idempotent)
         2. Configure via POST /api/netsnmp/general/set
-        3. Start/restart via POST /api/netsnmp/service/start
+        3. Start/restart the service
+        4. Add a floating firewall rule allowing UDP/161 from any source
+           (OPNsense default-drops traffic arriving on non-LAN interfaces
+           such as WireGuard; without this rule SNMP is unreachable from
+           management networks even though the daemon is running)
+        5. Apply firewall and verify
         """
         lines: list = []
 
-        # 1. Install os-net-snmp plugin (POST /api/core/firmware/install/os-net-snmp)
+        # 1. Install os-net-snmp plugin
         try:
             result = self._post("/api/core/firmware/install/os-net-snmp")
             lines.append(f"[install] {result}")
         except Exception as exc:
             logger.debug("os-net-snmp install skipped or failed: %s", exc)
-            lines.append(f"[install] skipped or already installed: {exc}")
+            lines.append(f"[install] already installed or skipped")
 
-        # 2. Configure SNMP: enable + set community 'public'
+        # 2. Configure SNMP
         try:
             self._post("/api/netsnmp/general/set", {
                 "general": {
@@ -1585,10 +1590,45 @@ class OPNsenseDriver(FirewallDriver):
                 self._post("/api/netsnmp/service/start")
                 lines.append("[service] net-snmp started.")
             except Exception as exc2:
-                logger.debug("SNMP service start failed: %s", exc2)
                 lines.append(f"[service] start failed: {exc2}")
 
-        # 4. Verify
+        # 4. Add floating firewall rule for SNMP (UDP/161 → self)
+        # OPNsense blocks traffic arriving on non-LAN interfaces by default.
+        # A floating pass rule makes SNMP reachable from all management nets.
+        try:
+            existing = self._post("/api/firewall/filter/searchRule",
+                                  {"current": 1, "rowCount": -1, "searchPhrase": "[netork] Allow SNMP"})
+            if not (existing.get("rows") or []):
+                self._post("/api/firewall/filter/addRule", {
+                    "rule": {
+                        "enabled": "1",
+                        "sequence": "1",
+                        "action": "pass",
+                        "quick": "1",
+                        "interface": "",        # floating — all interfaces
+                        "direction": "in",
+                        "ipprotocol": "inet",
+                        "protocol": "udp",
+                        "source_net": "any",
+                        "source_not": "0",
+                        "destination_net": "(self)",
+                        "destination_not": "0",
+                        "destination_port": "161",
+                        "log": "0",
+                        "floating": "yes",
+                        "descr": "[netork] Allow SNMP",
+                    }
+                })
+                lines.append("[firewall] Floating pass rule added for UDP/161.")
+            else:
+                lines.append("[firewall] Pass rule already present.")
+            self._post("/api/firewall/filter/apply", {})
+            lines.append("[firewall] Rules applied.")
+        except Exception as exc:
+            logger.debug("Firewall rule for SNMP failed: %s", exc)
+            lines.append(f"[firewall] error: {exc}")
+
+        # 5. Verify SNMP config
         try:
             cfg = self._get("/api/netsnmp/general/get")
             general = cfg.get("general", cfg)
@@ -1597,11 +1637,7 @@ class OPNsenseDriver(FirewallDriver):
             logger.debug("SNMP verification failed: %s", exc)
             success = False
 
-        if success:
+        lines.append("[ok] SNMP active." if success else "[warn] Could not verify SNMP state.")
-            lines.append("[ok] SNMP is active with community 'public'.")
-        else:
-            lines.append("[warn] Could not verify SNMP state via API.")
-
         return {"success": success, "output": "\n".join(lines)}
 
     def get_firewall_aliases(self) -> list[dict[str, Any]]: