From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark Borst Subject: Re: node-local multicast issues Date: Thu, 11 Nov 2004 13:21:53 +0200 Message-ID: <1100172113.24452.10.camel@mn-2> References: <1100096251.22964.7.camel@mn-2> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: hessu@cs.tut.fi, netdev@oss.sgi.com Return-path: To: David Stevens In-Reply-To: <1100096251.22964.7.camel@mn-2> Sender: netdev-bounce@oss.sgi.com Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org It's a pity that I have to reply to myself. On Wed, 2004-11-10 at 16:17 +0200, Mark Borst wrote: > On Tue, 2004-11-09 at 15:21 -0800, David Stevens wrote: > > The loopback device doesn't have IFF_MULTICAST set, so technically > > it is not a multicast-capable device, and you shouldn't be able to join a > > group on it. > > That is Linux-specific, right? At least KAME's 'lo' does support > multicast, and their README says: > > On Windows I don't see 'lo' joining ff01::1. > > RFC 3513 tells me: > > 2.7.1 Pre-Defined Multicast Addresses > > All Nodes Addresses: FF01:0:0:0:0:0:0:1 > FF02:0:0:0:0:0:0:1 > > The above multicast addresses identify the group of all IPv6 nodes, > within scope 1 (interface-local) or 2 (link-local). > > Does that imply that the linux stack doesn't conform to RFC 3513? My tests show that interface-local multicast actually works, when I get my implementation right. So interface-local multicast on 'lo' does work. However, pinging ff01::1 on 'lo' still doesn't get me any reply. > > > I think the way it ought to work is that you join the group on any device, > > with IPV6_MULTICAST_LOOP set and local guys should hear the node-local > > multicasts, but it shouldn't be sent on the wire. Multicasting could be supported on > > loopback, too, but it doesn't matter all that much unless there are no multicast-capable > > real devices. > > > However, it appears that node-local multicasts are being sent out > > the device, at least on an early 2.6 kernel I did a quick test with. There probably > > isn't anything enforcing the node-locality in the send path, which I would consider a > > bug. :-) > > Even more interesting: an other node responded to 'ping6 ff01::1' so > there is some bug somewhere ;) > > On another note: 'ping6 ff02::1' gives "connect: Invalid argument" on > linux. On KAME it says "ping6: UDP connect: Network is unreachable". The > only implementation that gives me replies is Solaris. This also sounds > like a bug to me. As already mentioned, one needs to specify the interface with -I to make it work. -- Mark Borst Researcher Network and Protocols Group Tampere University of Technology, Finland