How to send Multicast packets

How to send Multicast packets

Post by Vish Viswanatha » Tue, 02 Mar 1999 04:00:00

I have a problem sending multicast packets in my linux system. I have a UDP
program which needs to send multicast packets addressed to (which
is a clss D address). If I call 'sendto' with this address, i get a "network
unreachable" error. However, if I add this address to the router table with
the command
        route add -host eth0
then it works ok.
My 'ifconfig' command shows 'multicast' enabled.

Shouldn't the system automatically figure out that this is a multicast
address and do the right thing. Why should I add each multicast address that
I am interested in to the router table.


Could somebody tell me what I am missing here?.



1. Sending multicast packet on a raw socket

Dear all,

I'm currently trying to write a small program which sends igmp query out on
my LAN. It is currently working fine under different version of FreeBSD.
Packets are sent out on the Network and I can see them arriving on my
different routers.
I compiled this program on Solaris 8 (using gcc 2.95.2). So far so good but
when I execute it there are no packets sent out on my networks !!!!

The call I do to send the packets is easy:

nbs = sendto(s,&pkt,sizeof(struct igmp),0,(struct sockaddr *)sa,salen);
  if ( nbs < 0 ) {
    perror("Sending query");
    return FALSE;

and creation of the socket is done like this:

  if ( lsq < 0 ) {
    perror("Creation of listening socket");
    return NULL;

Has any body any idea what the problem could be ? Should I configure smth
special on the socket in order to make it run under Solaris ?

Thank you in advance for any help

Laurent Bourqui
Grubenstrasse 7
CH-3322 Sch?nbhl
+41 (0)31 858 58 58

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