From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id F38D5C2B9F4 for ; Thu, 17 Jun 2021 12:33:20 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D28A860E08 for ; Thu, 17 Jun 2021 12:33:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230391AbhFQMf1 (ORCPT ); Thu, 17 Jun 2021 08:35:27 -0400 Received: from mail.aperture-lab.de ([116.203.183.178]:45452 "EHLO mail.aperture-lab.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230316AbhFQMfZ (ORCPT ); Thu, 17 Jun 2021 08:35:25 -0400 Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPSA id 3F0303E904; Thu, 17 Jun 2021 14:33:12 +0200 (CEST) Date: Thu, 17 Jun 2021 14:33:09 +0200 From: Linus =?utf-8?Q?L=C3=BCssing?= To: Callum Sinclair Cc: dsahern@kernel.org, nikolay@nvidia.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, troglobit@gmail.com Subject: Re: [PATCH 1/1] net: Allow all multicast packets to be received on a interface. Message-ID: <20210617123309.GB2262@otheros> References: <20210617095020.28628-1-callum.sinclair@alliedtelesis.co.nz> <20210617095020.28628-2-callum.sinclair@alliedtelesis.co.nz> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210617095020.28628-2-callum.sinclair@alliedtelesis.co.nz> User-Agent: Mutt/1.10.1 (2018-07-13) X-Last-TLS-Session-Version: TLSv1.2 Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Hi Callum, On Thu, Jun 17, 2021 at 09:50:20PM +1200, Callum Sinclair wrote: > +mc_snooping - BOOLEAN > + Enable multicast snooping on the interface. This allows any given > + multicast group to be received without explicitly being joined. > + The kernel needs to be compiled with CONFIG_MROUTE and/or > + CONFIG_IPV6_MROUTE. > + conf/all/mc_snooping must also be set to TRUE to enable multicast > + snooping for the interface. > + Generally this sounds like a useful feature. One note: When there are snooping bridges/switches involved, you might run into issues in receiving all multicast packets, as due to the missing IGMP/MLD reports the snooping switches won't forward to you. In that case, to conform to RFC4541 you would also need to become the selected IGMP/MLD querier and send IGMP/MLD query messages. Or better, you'd need to send Multicast Router Advertisements (RFC4286). The latter is the recommended, more flexible way but might not be supported by all multicast snooping switches yet. The Linux bridge supports this. There is a userspace tool called mrdisc you can use for MRD-Adv. though: https://github.com/troglobit/mrdisc. So no need to implement MRD Advertisements in the kernel with this patch (though I could imagine that it might be a useful feature to have, having MRD support out-of-the-box with this option). Just a note that some IGMP/MLD Querier or MRD Adv. would be needed when IGMP/MLD snooping switches are invoved might be nice to have in the mc_snooping description for now, to avoid potential confusion later. I'm also wondering if it could be useful to configure it via setsockopt() per application instead of per device via sysctl. Either by adding a new socket option. Or by allowing the any IP address 0.0.0.0 / :: with IP_ADD_MEMBERSHIP/IPV6_JOIN_GROUP. So that you could use this for instance: $ socat -u UDP6-RECV:1234,reuseaddr,ipv6-join-group="[::]:eth0" - (currently :: fails with "Invalid argument") I'm not sure however what the requirements for adding or extending socket options are, if there are some POSIX standards that'd need to be followed for compatibility with other OSes, for instance. Hm, actually, I just noticed that there seem to be some multicast related setsockopt()s already: - PACKET_MR_PROMISC - PACKET_MR_MULTICAST - PACKET_MR_ALLMULTI The last one seems to be what you are looking for, I think, the manpage here says: "PACKET_MR_ALLMULTI sets the socket up to receive all multicast packets arriving at the interface" https://www.man7.org/linux/man-pages/man7/packet.7.html Or would you prefer to be able to use a layer 3 IP instead of a layer 2 packet socket? Regards, Linus