udp vs. multicast group

(Didier, I am still struggling with udp stuff...) Hey folks! Have you tried to use `open-multicast-group'? (open-multicast-group "test" "test" "127.0.0.1/7/15") => Signaling: (file-error "error adding membership" "Invalid argument" "test" "127.0.0.1") open-multicast-group-internal("test" "test" "127.0.0.1" 7 15) open-multicast-group("test" "test" "127.0.0.1/7/15") eval((open-multicast-group "test" "test" "127.0.0.1/7/15")) eval-interactive((open-multicast-group "test" "test" "127.0.0.1/7/15")) eval-last-sexp(nil) call-interactively(eval-last-sexp) Same error even if I restrict address between 224.0.0.0 and 239.255.255.255 (why these?) Shouldn't udp as simple as tcp code? This works very well: (open-network-stream "test2" "test2" "127.0.0.1" 7) What I actually try to do is: ;;; ip = icq1.mirabilis.com (open-multicast-group "test" "test" "205.188.252.216/4000/127") Thank you.