From mboxrd@z Thu Jan 1 00:00:00 1970 From: William Manley Subject: IGMP Unsolicited Report Interval too long for IGMPv3? Date: Mon, 22 Jul 2013 21:43:57 +0100 Message-ID: <51ED998D.7000300@youview.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit To: Return-path: Received: from mail-db9lp0252.outbound.messaging.microsoft.com ([213.199.154.252]:41874 "EHLO db9outboundpool.messaging.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933328Ab3GVUoY (ORCPT ); Mon, 22 Jul 2013 16:44:24 -0400 Received: from mail38-db9 (localhost [127.0.0.1]) by mail38-db9-R.bigfish.com (Postfix) with ESMTP id 75E5760130 for ; Mon, 22 Jul 2013 20:44:22 +0000 (UTC) Received: from DB9EHSMHS011.bigfish.com (unknown [10.174.16.249]) by mail38-db9.bigfish.com (Postfix) with ESMTP id D91BF460046 for ; Mon, 22 Jul 2013 20:44:20 +0000 (UTC) Sender: netdev-owner@vger.kernel.org List-ID: 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. 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