Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261821AbUDSUH2 (ORCPT ); Mon, 19 Apr 2004 16:07:28 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261830AbUDSUH2 (ORCPT ); Mon, 19 Apr 2004 16:07:28 -0400 Received: from 213-0-215-223.dialup.nuria.telefonica-data.net ([213.0.215.223]:57992 "EHLO dardhal.mired.net") by vger.kernel.org with ESMTP id S261821AbUDSUH0 (ORCPT ); Mon, 19 Apr 2004 16:07:26 -0400 Date: Mon, 19 Apr 2004 22:07:40 +0200 From: Jose Luis Domingo Lopez To: John Pesce Cc: linux-kernel@vger.kernel.org Subject: Re: How to make Linux route multicast traffic bi-directionly between multible subnets Message-ID: <20040419200739.GA3020@localhost> Mail-Followup-To: John Pesce , linux-kernel@vger.kernel.org References: <1082389059.1982.15.camel@inferno> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1082389059.1982.15.camel@inferno> User-Agent: Mutt/1.5.5.1+cvs20040105i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2470 Lines: 54 On Monday, 19 April 2004, at 11:37:39 -0400, John Pesce wrote: > The only thing I have been able to do is set a default multicast route > to subnet A. This forwards traffic incoming from B and C to A, but what > about the other ways? > With that default route for multicast traffic the only thing you do is route through some interface the multicast traffic for which there are no more specific routes. Multicast routing is in some ways different from unicast routing: with multicast you must be able to send several copies on the original incoming packet through one or more outgoing interfaces, namely those that lead to hosts and networks somewhat "subscribed" to a multicast group (the destination multicast IP in the IP packet). As far as I know, there is no userspace tool (not saying that you can't write one :) to insert multicast routes directly in the kernel routing table (at least, I was not able to do anything with "ip"). > I see on bootup a kernel message about 0.96 PIM-SM. Can I somehow use > that? > The only way I know to make a Linux box route multicast traffic "as expected" is to configure a multicast routing daemon like "mrouted". It should listen on all interfaces declared as multicast, see IGMP packets coming from hosts interested in some multicast groups (interested in receiving traffic to some multicast IP addresses) and route incoming multicast packets accordingly (sending several copies of the same packet through all needed interfaces). The message you see in the kernel boot log refers to one of the protocols used for dynamic multicast routing, namely PIM-SM (Protocol Independent Multicast, Sparse Mode). This protocol is implemented by "mrouted", but seems to need some specific support from kernel space to work properly (other dynamic multicast routing protocols implemented by "mrouted" don't seem to show this requirment). So, to summarize, your best bet is to get "mrouted" or something like that, and have a look at the documentation bundled. You are quite right, multicast routing documentation for Linux seems to be quite old, rather short, and maybe out of date. Greetings. -- Jose Luis Domingo Lopez Linux Registered User #189436 Debian Linux Sid (Linux 2.6.5) - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/