WifiNinaUdp not receiving broadcast messages

[romanini]

I am trying to have my Nano 33 IoT listen to UDP broadcast packets from a server. I need this because I'll have several devices connected to a central arduino and I want to send status to all of them. The code I have is a slight modification of the example but structurally the same:

#include <WiFiNINA.h>
#include <WiFiUdp.h>

// WiFi credentials
char ssid[] = "";
char pass[] = "";

IPAddress broadcastIp(10,20,1,255);

unsigned int localPort = 8888; // local port to listen on

WiFiUDP Udp;

unsigned long timestamp;

void setup() {
//Initialize serial and wait for port to open:
Serial.begin(9600);
while (!Serial); // wait for serial port to connect

// check for the WiFi module:
if (WiFi.status() == WL_NO_MODULE) {
Serial.println("Communication with WiFi module failed!");
// don't continue
while (true);
}

String fv = WiFi.firmwareVersion();
if (fv < WIFI_FIRMWARE_LATEST_VERSION) {
Serial.println("Please upgrade the firmware");
}

// attempt to connect to Wifi network:
int status = WL_IDLE_STATUS;
while (status != WL_CONNECTED) {
Serial.print("Attempting to connect to SSID: ");
Serial.println(ssid);
// Connect to WPA/WPA2 network. Change this line if using open or WEP network:
status = WiFi.begin(ssid, pass);


// wait 10 seconds for connection:
delay(10000);


}
Serial.println("Connected to WiFi");
printWifiStatus();

Serial.println("\nStarting connection to server...");

Udp.begin(localPort);
}

void loop() {
// periodically send a message
if (millis() - timestamp > 3000) {
Serial.println("Sending");
Udp.beginPacket(broadcastIp, localPort);
Udp.write("hello");
Udp.endPacket();
timestamp = millis();
}

// if there's data available, read a packet
int packetSize = Udp.parsePacket();
if (packetSize) {
Serial.print("Received packet of size ");
Serial.println(packetSize);
Serial.print("From ");
IPAddress remoteIp = Udp.remoteIP();
Serial.print(remoteIp);
Serial.print(", port ");
Serial.println(Udp.remotePort());


char packetBuffer[255]; //buffer to hold incoming packet
// read the packet into packetBufffer
int len = Udp.read(packetBuffer, sizeof(packetBuffer) / sizeof(packetBuffer[0]));
if (len > 0) {
packetBuffer[len] = 0;
}
Serial.println("Contents:");
Serial.println(packetBuffer);


}
}

void printWifiStatus() {
// print the SSID of the network you're attached to:
Serial.print("SSID: ");
Serial.println(WiFi.SSID());

// print your board's IP address:
IPAddress ip = WiFi.localIP();
Serial.print("IP Address: ");
Serial.println(ip);

// print the received signal strength:
long rssi = WiFi.RSSI();
Serial.print("signal strength (RSSI):");
Serial.print(rssi);
Serial.println(" dBm");
}

This code runs and I can see that I'm sending a broadcast packet and I can receive it on other devices in the network using
nc -luvw0 8888 so I know it is sending. However I don't receive anything on the arduino (ie in my loop I never get anything. IF I modify the sending from what it is now

Udp.beginPacket(broadcastIp, localPort);

to be

Udp.beginPacket(WiFi.localIP(), localPort);

that is to send the UDP packet directly to the device rather than a broadcast message. Then the arduino gets the message, but of course no other device in the network gets it.

How can I receive broadcast packets?