Receiving data from UDP server on iOS app is not working from Linux server, but works

-(void)viewDidLoad
{
    [super viewDidLoad];
    backGround.userInteractionEnabled=YES;  
    udpSocket = [[GCDAsyncUdpSocket alloc] initWithDelegate:self delegateQueue:dispatch_get_main_queue()];

    NSError *error = nil;
    if (![udpSocket bindToPort:0 error:&error]) //check ff of dit werkt!
    {
        return;
    }
    if (![udpSocket beginReceiving:&error])
    {
        return;
    }
}


- (IBAction)sendData:(id)sender 
{
    NSString *msg = messageField.text;
    NSData *data = [msg dataUsingEncoding:NSUTF8StringEncoding];
    [self sendingRealData:data];
}

-(void)sendingRealData:(NSData *) Content
{
    NSString *msg = [[NSString alloc] initWithData:Content encoding:NSUTF8StringEncoding];
    NSLog(@\"msg is: %@\", msg);
    NSString *host = [self getHost];
    int port = [self getPort]; 

    if ((port == 65536) && (host == @\"-1\"))
    {
        NSLog(@\"Port and IP are not filled in!\");
        [self errorManag:2]; 
    }

    else if ((port == 65536) && (host != @\"-1\"))
    {
        NSLog(@\"return was -2\");
        [self errorManag:1];
    }

    else if (host == @\"-1\")
    {
        NSLog(@\"return was -1\");
        [self errorManag:0]; 
    }

    else 
    {
        [udpSocket sendData:Content toHost:host port:port withTimeout:1 tag:tag];
        NSLog(@\"Gestuurd\");
    }
}

- (void)udpSocket:(GCDAsyncUdpSocket *)sock didReceiveData:(NSData *)data
  fromAddress:(NSData *)address
withFilterContext:(id)filterContext
{
    NSLog(@\"niets.\"); 
    NSString *msg = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
if (msg)
{
        NSLog(@\"iets gekregen\");
}
else
{
    NSLog(@\"Error conversion\");
    //[self logError:@\"Error converting received data into UTF-8 String\"];
}
//NSString *test = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
//NSLog(@\"%@\",test); 
//[udpSocket sendData:data toAddress:address withTimeout:-1 tag:0];
    NSLog(@\"HMMMM\");
    messageField.text = [[NSString alloc] initWithFormat:@\"RE: %@\", msg]; 
}