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[lwip-users] LWIP + IGMP

From: Ricardo Schoof
Subject: [lwip-users] LWIP + IGMP
Date: Tue, 7 Apr 2015 16:33:27 +0200

Dear all,


I want to receive UDP-packets from a multicast message. The system currently can receive unicast messages.


To receive multicast messages I’ve set the following settings in lwipopts.h

  #define LWIP_IGMP                       1

  #define MEMP_NUM_IGMP_GROUP             8


Also in the initialize function I’ve set the right flag



The initializing of the IGMP-group is as follows

 uint16 port;

  ip_addr_t groupAddress;


  getParamatersFromTransmissionGroup (group, &port, &groupAddress);

  __udpSocket = udp_new ();

  MF_ASSERT (__udpSocket != NULL);


  err_t err = udp_bind (__udpSocket, IP_ADDR_ANY, port);

  MF_ASSERT (err == ERR_OK);


  err = igmp_joingroup (&localAddr, &groupAddress);

  MF_ASSERT (err == ERR_OK);


  udp_recv (__udpSocket, data_received, this);


When I send data directly to the IP address assigned in LWIP I get to the breakpoint in data_received.

However when I change the destination IP address to the one configured in groupAddress, I get no data at all.


I’ve made some tests in Wireshark where I captured the packets. The test system consists of three devices > Router > Computer with Wireshark > LWIP Device

I’ve attached the capturefile done in Wireshark, In this file you can see the LWIP device responds to a query.

If you need any more information, please reply to this mail.


Met vriendelijke groet, Best regards,


Ricardo Schoof | R&D Engineer

Attachment: capture.pcapng
Description: capture.pcapng

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