Multicast UDP socket

Question

I would like to open a UDP socket that sends data to a multicast group and receives unicast messages. My current configuration is to open a UDP socket with: socket(4, Sn_MR_UDP, 2222, SF_BROAD_BLOCK); and send the data with sendto( 4, *message_buffer, message_length, multicastAddr, 2222); The problem is that, although the multicast address is correct, the destination MAC address is the MAC address of the receiving device, not the multicast hardware address.

Eugeny · Answer

W5500 Broadcast Server - TCP/IP Chip / W5500 - WIZnet Developer Forum maybe this will help?

Eugeny · Answer

Look at the W6100 datasheet chapter 6.3.3, this may give some good idea. It seems MC must not have ARP done, therefore try using SEND_MAC.

Vien Huy Nguyen · Answer

In chapter 6.3.3, it looks like I have to set the appropriate DHAR register myself. In this multicast example provided by WIZnet, they never set DHAR, I am not sure how this works: https://github.com/Wiznet/ioLibrary_Driver/blob/master/Application/multicast/multicast.c Also in the W5500 datasheet section 4.2, for multicasting in UDP mode, it says to set Sn_DIPR & Sn_DPORT, it does not say anything about Sn_DHAR.