iOS devices not receiving UDP multicast using GDAsyncUdpSocket - ios

Question

The code below is intended to receive UDP multicast messages on 239.255.255.250 and simply NSLog the contents of the message.
If I address a message to the IP of the iOS device (i.e. from a terminal echo foo | nc -u 10.1.10.249 1900) the message is received and NSLog'd.
However, if I broadcast a message to the multicast address (echo bar | nc -u 239.255.255.250 1900), the message is not received.
No error messages are logged at start up.
Thoughts on where I'm going awry?
#import "ViewController.h"
#import "GCDAsyncUdpSocket.h"
#interface ViewController () {
GCDAsyncUdpSocket *udpSocket;
}
#end
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
udpSocket = [[GCDAsyncUdpSocket alloc] initWithDelegate:self delegateQueue:dispatch_get_main_queue()];
NSError *error = nil;
if (![udpSocket bindToPort:1900 error:&error]) {
NSLog(#"Error starting server (bind): %#", error.description );
return;
}
if(![udpSocket joinMulticastGroup:#"239.255.255.250" error:&error] ) { //]onInterface:#"en0" error:&error]) {
NSLog(#"Error joining multicast group: %#",error.description);
return;
}
if (![udpSocket beginReceiving:&error]) {
[udpSocket close];
NSLog(#"Error starting server (recv): %#", error.description);
return;
}
NSLog(#"Udp server started on port %#:%hu", [udpSocket localHost_IPv4], [udpSocket localPort]);
}
- (void)udpSocket:(GCDAsyncUdpSocket *)sock didReceiveData:(NSData *)data fromAddress:(NSData *)address withFilterContext:(id)filterContext {
NSString *msg = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
NSLog(#"message rec'd: %#:%hu %#\n", [udpSocket localHost_IPv4], [udpSocket localPort],msg);
}
- (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
}
#end

Answer 1

You're missing a key function that stumped me for a time, too.
[udpSocket enableBroadcast:YES error:&error];
This will allow you to send broadcast packets and receive broadcasted packets from your multicast group.