From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Borkmann Subject: Re: [PATCH net-next 2/3] ipv6: mld: do not overwrite uri when receiving an mldv2 query Date: Thu, 25 Sep 2014 22:06:59 +0200 Message-ID: <542475E3.6030508@redhat.com> References: <1411455828-5196-1-git-send-email-dborkman@redhat.com> <1411455828-5196-3-git-send-email-dborkman@redhat.com> <54243C89.6060405@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: davem@davemloft.net, hannes@stressinduktion.org, netdev@vger.kernel.org To: David L Stevens Return-path: Received: from mx1.redhat.com ([209.132.183.28]:59835 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751939AbaIYUH0 (ORCPT ); Thu, 25 Sep 2014 16:07:26 -0400 In-Reply-To: <54243C89.6060405@oracle.com> Sender: netdev-owner@vger.kernel.org List-ID: On 09/25/2014 06:02 PM, David L Stevens wrote: > While I can see the case you're making, I think the intent of MRC is > violated by arbitrary URI. > >> 5.1.3. Maximum Response Code >> >> The Maximum Response Code field specifies the maximum time allowed >> before sending a responding Report. >> ... >> Small values of Maximum Response Delay allow MLDv2 routers to tune >> the "leave latency" (the time between the moment the last node on a >> link ceases to listen to a specific multicast address and the moment >> the routing protocol is notified that there are no more listeners for >> that address). Larger values, especially in the exponential range, >> allow the tuning of the burstiness of MLD traffic on a link. > > If URI is larger than MRD, then a lost unsolicited report, or series, > specifically will *not* propagate changes throughout the network in less > than MRD*QRV, as intended. > > It was an intentional design choice, not required or prohibited by RFC. > > I'm not sure what problem you think it's causing, but if they are not > equal, I think at least the URI should be enforced to <= MRD. The querier, > IMO, should set these network-wide relevant parameters, not the individual > hosts. One of the problems I see (also with this argumentation -- next to the fact that it's not specified by the RFC) is that we're blindly overwriting with any given value from the MLDv2 query, while when temporarily transitioning back to MLDv1 compatibility mode, we're simply ignoring any MLD value provided from that query; both specifications also specify different default values for URI, where we would have already overwritten a pre-configured URI default value for v1 when we previously received a v2 query. While we have tunable for IPv4 case via commit 2690048c01f32 ("net: igmp: Allow user-space configuration of igmp unsolicited report interval") and for IPv6 case via commit fc4eba58b4c1 ("ipv6: make unsolicited report intervals configurable for mld"), this renders any admin provided IPv6 specific configuration useless. Thanks, Daniel