Has anyone tried IP multicast with RTEMS?

Thomas Rauscher trauscher at loytec.com
Tue Oct 21 06:33:40 UTC 2003

> -----Original Message-----
> From: Phil Torre [mailto:ptorre at zetron.com]
> Sent: Monday, October 20, 2003 8:16 PM
> To: RTEMS User List
> Subject: Has anyone tried IP multicast with RTEMS?
> Greetings All,
> Can anyone report success with RTEMS and multicast?  From what I can
> tell by looking through the source, it looks like the FreeBSD stack
> is multicast-capable, but I may have some work to do in the Ethernet
> device driver (for MPC860, as used in the eth_comm BSP).
> I haven't done any experiments yet, but we will want to be doing
> multicast in future product development, so I'm just looking ahead.
> Thanks,
> -Phil

Multicasting works. Basically, two things are important:

1) Ethernet layer:
   The driver must support ethernet multicasting. That is, it must
   configure its ethernet multicast list/hash table when
   a socket joins a multicast group.

   This is done in the driver's ioctl. Required commands

   There is a macro ETHER_MAP_IP_MULTICAST to map IP addresses
   and ethernet multicast addresses. 

2) IP layer:
   Sending works immediately by just using an IP multicast address.
   Receiving requires to add the node to an IP multicast group
   (so that IP/Ethernet multicasting is configured properly).
   This is done like in the code snippet below.

    #include <sys/socket.h>                                                         
    #include <sys/sockio.h>                                                         
    #include <net/if.h>                                                             
    #include <netinet/in.h>                                                         
    #include <netinet/if_ether.h>                                                   
    struct ip_mreq mreq;        
    int            fd;                                                  
    if (setsockopt(fd,IPPROTO_IP,IP_ADD_MEMBERSHIP,&mreq,sizeof(mreq)) < 0) {

Best regards,

Dipl.-Ing. Thomas Rauscher                 Tel.:   ++43 1 402 08 05 15
                                           Fax:    ++43 1 402 08 05 99
LOYTEC electronics GmbH                    E-mail: trauscher at loytec.com
Stolzenthalergasse 24/3, A-1080 Wien       Web:    http://www.loytec.com

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