From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vlad Yasevich Subject: multicast: bug or "feature" Date: Wed, 17 Oct 2007 15:58:05 -0400 Message-ID: <4716694D.6030508@hp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Brian Haley To: netdev Return-path: Received: from atlrel9.hp.com ([156.153.255.214]:53545 "EHLO atlrel9.hp.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1763284AbXJQT60 (ORCPT ); Wed, 17 Oct 2007 15:58:26 -0400 Received: from smtp2.fc.hp.com (smtp2.fc.hp.com [15.11.136.114]) by atlrel9.hp.com (Postfix) with ESMTP id 62A8035A04 for ; Wed, 17 Oct 2007 15:58:06 -0400 (EDT) Sender: netdev-owner@vger.kernel.org List-Id: netdev.vger.kernel.org We've been trying to field some questions regarding multicast behavior and one such behavior has stumped us. I've reproduced the following behavior on 2.6.23. The application opens 2 sockets. One socket is the receiver and it simply binds to 0.0.0.0:2000 and joins a multicast group on interface eth0 (for the test we used 224.0.1.3). The other socket is the sender. It turns off MULTICAST_LOOP, sets MULTICAST_IF to eth1, and sends a packet to the group that the first socket joined. We are expecting to receive the data on the receiver socket, but nothing comes back. Running tcpdump on both interfaces during the test, I see the packet on both interfaces, ie. I see it sent on eth0 and received on eth1 with IP statistics going up appropriately. Looking at the group memberships, I see the receiving interface as part of the group and IGMP messages were on the wire. So, before I try to spend time figuring out where the packet went is why, I'd like to know if this is a Linux "feature". Thanks -vlad