hello jggimi and thanks very much for your reply.
I use OpenBSD 5.5 with the matching quagga (installed with the pkg_add command)
I already set multicast_router=YES in /etc/rc.conf.local but it still doesn't work.
I've also uncommented all the rows in sysctl.conf about forwarding ipv4 and multicast ipv4 packets
what should I do?