From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin LaHaise Subject: Re: IGMP Unsolicited Report Interval too long for IGMPv3? Date: Mon, 22 Jul 2013 17:18:55 -0400 Message-ID: <20130722211855.GL19643@kvack.org> References: <51ED998D.7000300@youview.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org To: William Manley Return-path: Received: from kanga.kvack.org ([205.233.56.17]:45351 "EHLO kanga.kvack.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932585Ab3GVVS6 (ORCPT ); Mon, 22 Jul 2013 17:18:58 -0400 Content-Disposition: inline In-Reply-To: <51ED998D.7000300@youview.com> Sender: netdev-owner@vger.kernel.org List-ID: On Mon, Jul 22, 2013 at 09:43:57PM +0100, William Manley wrote: > If an IGMP join packet is lost you will not receive data sent to the > multicast group so if no data arrives from that multicast group in a > period of time after the IGMP join a second IGMP join will be sent. The > delay between joins is the "IGMP Unsolicited Report Interval". > > In the kernel this seems to be hard coded to be chosen randomly between > 0-10s. In our use-case (IPTV) this is too long as it can cause channel > change to be slow in the presence of packet loss. > > I would guess that this 10s has come from IGMPv2 RFC2236, which was > reduced to 1s in IGMPv3 RFC3376. Reducing the timeout does not solve the problem you are encountering, as any packet loss will still result in a 1 second delay. I've encountered similar issues dealing with LCP Echo request/replies for keepalive messages on PPP sessions. The correct approach is to queue the IGMP multicast join with a higher priority than other traffic in the system so that the requests are not lost due to congestion of a single queue. Sending packets with an 802.1p header might be appropriate in your use-case, or perhaps using higher priority internal queues. -ben > There was a thread about this on linux-rdma in 2010 in the context of IP > over Infiniband but it seems no patches got applied as a result of the > discussion: > > http://www.mail-archive.com/linux-rdma@vger.kernel.org/msg05740.html > > Would the right patch reducing the unsolicited report interval for > IGMPv3 be acceptable now? > > Thanks > > Will > > > -- > To unsubscribe from this list: send the line "unsubscribe netdev" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- "Thought is the essence of where you are now."