fix(ns-ha): send gratuitous ARP for WANs

Keepalived automatically send gratuitous ARP for tracked interfaces.
Since WAN interfaces are not tracked, gratuitous ARP packets
must be sent just after the switch to master.

Author: gsanchietti

packages/ns-ha/files/ns-ha-enable

@@ -39,6 +39,38 @@ def enable_interfaces(file):
             # Return code of ifup is not reliable, so we do not check it nor log it
             logger.info("Bringing up interface %s", interface)
 
+def send_gratuitous_arp(file):
+    # Get the mapping interface -> device
+    proc = subprocess.run(["ubus", "-v", "call", "network.interface", "dump"], capture_output=True, text=True)
+    try:
+        network_dump = json.loads(proc.stdout)
+    except json.JSONDecodeError:
+        logger.error("Can't send gratuitous ARP: failed to decode JSON from network dump")
+        return
+    device_map = {}
+    for iface in network_dump.get('interface', []):
+        if 'device' in iface and 'interface' in iface:
+            device_map[iface['interface']] = iface['device']
+    # Load the file with the interfaces to send gratuitous ARP for
+    with open(os.path.join(out_dir, file), 'r') as f:
+        interfaces = json.load(f)
+    for interface in interfaces:
+        if 'ipaddr' in interfaces[interface]:
+            device = device_map.get(interface)
+            if not device:
+                logger.error("Can't send gratuitous ARP: no device found for interface %s", interface)
+                continue
+            # It should not happen, but ipaddr can contain multiple IPs
+            ipaddr = interfaces[interface]['ipaddr']
+            if isinstance(ipaddr, str):
+                ipaddr = [ipaddr]
+            for ip in ipaddr:
+                # Remove /mask if present
+                ip = ip.split('/')[0]
+                # Send gratuitous ARP to update switches ARP tables
+                aproc = subprocess.run(["/usr/bin/arping", "-c", "1", "-U", "-I", device, ip], capture_output=True)
+                logger.info("Sending gratuitous ARP on interface %s (%s) for IP %s: %s", interface, device, ip, "success" if aproc.returncode == 0 else "fail")
+
 def enable_hotspot_mac():
     u = EUci()
     devices = utils.get_all_by_type(u, 'network', 'device')
@@ -60,4 +92,5 @@ if __name__ == "__main__":
     enable_interfaces('wg_interfaces')
     enable_interfaces('ipsec_interfaces')
     enable_hotspot_mac()
+    send_gratuitous_arp('wan_interfaces')
     subprocess.run(["/sbin/reload_config"], capture_output=True)