WIZnet Developer Forum

Wiznet W5500 in Mulitcast Environment

we are using the WIZ550 io module containing the Wiznet W5500 chip in a
multicast environment. Direct receive and send functionality works
fine, but when opening a multicast socket, only a ‘Report Group’ IGMP
message but no ‘Join Group’ message is transmitted.

According to the description at

wizwiki.net/wiki/doku.php?id=pro … #multicast

a ‘Join Group’ message should be sent automatically when opening the
socket. Unfortunately, the switches require the ‘Join Group’ message as
a ‘Report Group’ message does not register the device as recipient.

Is there any point we are missing which causes this behavior? Or does
the W5500 generally not transmit ‘Join Group’ messages.

Thank you,


we finally found the solution for the problem. It is not at all a problem of the IGMP implementation in the WIZnet, but we missed the fact that only 23 bits of the multicast destination hardware address are the same as the multicast destination ip address. We used 24 bits instead and which made the switch reject the packets. Now everything work fine.


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