UDP Multicast MAC not correct?

[showengineer]

When sending something to a multicast address (e.g 225.1.2.1), a UDP packet gets properly sent (verified with Wireshark). However, my receiver doesn't get the package.

I've tested my network and its multicasting capabilities with this program. Using the same receiver program, it doesn't get the UDP packets from my Arduino.

I have found that the only difference between the packet sent with the example program and the Arduino is the destination MAC.

The library/Arduino sets its destination MAC to FF:FF:FF:FF:FF:FF (Broadcast). While the socket in Windows sets the destination MAC to 01:00:5E:01:02:01 (IPv4mcast_01:02:01).

Is this why my receivers aren't receiving UDP packets from the Arduino or is it still my fault?

[nuno-silva]

To receive multicast on the Arduino you need to call enableMulticast():

EtherCard/src/enc28j60.h

Lines 118 to 121 in 39a1188

	/** @brief Enables reception of multicast messages
	* @note This will increase load on received data handling
	*/
	static void enableMulticast ();

However, your problem seems to be sending from the Arduino, right?

[showengineer]

Correct

[nuno-silva]

I'd say give enableMulticast() a try anyway. I'm not sure sending multicast packets is implemented though.

[njh]

I have just done a test using socat on my Mac:

echo "Hello World" | socat -u - udp-datagram:225.1.2.1:1234

And can see the packets going to 01:00:5e:01:02:01 using Wireshark.

The code that sets the MAC address for broadcast/multicast addresses is here:
https://github.com/njh/EtherCard/blob/master/src/tcpip.cpp#L384

So it indeed just sets it to FF:FF:FF:FF:FF:FF.
I am a big fan of multicast, so would like to see this working.
I am surprised that your network switch cares - what sort of switch do you have?

I have a very old Ethernet hub that I sometimes use for testing Ethercard - because it blindly copies all packets to all ports, making it easier to diagnose what is going on.

[showengineer]

I am surprised that your network switch cares - what sort of switch do you have?

I am using a Netgear GS108, with nothing more than my PC and the arduino board connected to it. I have tried sending packets over my main network but no results so far.

I did try hardcoding the correct multicast MAC (01:00:5e:01:02:01) as the destination mac, but the packets didn't show up in Wireshark.