From: Philip Downey <pdowney@Brocade.com>
To: Thadeu Lima de Souza Cascardo <cascardo@redhat.com>,
Andrew Lunn <andrew@lunn.ch>
Cc: David Miller <davem@davemloft.net>,
"kuznet@ms2.inr.ac.ru" <kuznet@ms2.inr.ac.ru>,
"jmorris@namei.org" <jmorris@namei.org>,
"yoshfuji@linux-ipv6.org" <yoshfuji@linux-ipv6.org>,
"kaber@trash.net" <kaber@trash.net>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>
Subject: RE: [PATCH] IGMP: Inhibit reports for local multicast groups
Date: Fri, 14 Aug 2015 08:55:38 +0000 [thread overview]
Message-ID: <043c875965404398bc769cfce1209718@EMEAWP-EXMB12.corp.brocade.com> (raw)
In-Reply-To: <20150813180809.GB22268@indiana.gru.redhat.com>
Sorry for the duplication - I responded in a similar manner before seeing this.
Thanks
Philip
> -----Original Message-----
> From: Thadeu Lima de Souza Cascardo [mailto:cascardo@redhat.com]
> Sent: Thursday, August 13, 2015 7:08 PM
> To: Andrew Lunn
> Cc: Philip Downey; David Miller; kuznet@ms2.inr.ac.ru; jmorris@namei.org;
> yoshfuji@linux-ipv6.org; kaber@trash.net; linux-kernel@vger.kernel.org;
> netdev@vger.kernel.org
> Subject: Re: [PATCH] IGMP: Inhibit reports for local multicast groups
>
> On Thu, Aug 13, 2015 at 07:01:37PM +0200, Andrew Lunn wrote:
> > On Thu, Aug 13, 2015 at 04:52:32PM +0000, Philip Downey wrote:
> > > Hi Andrew
> > > IGMP snooping is designed to prevent hosts on a local network from
> receiving traffic for a multicast group they have not explicitly joined. Link-
> Local multicast traffic should not have an IGMP client since it is reserved for
> routing protocols. One would expect that IGMP snooping needs to ignore
> local multicast traffic in the reserved range intended for routers since there
> should be no IGMP client to make "join" requests.
> >
> > The point of this patch is that Linux is sending out group membership
> > for these addresses, it is acting as a client. What happens with a
> > switch which is applying IGMP snooping to link-local multicast groups?
> > You turn on this feature, and you no longer get your routing protocol
> > messages.
> >
> > I had a quick look at RFC 3376. The only mention i spotted for not
> > sending IGMP messages is:
> >
> > The all-systems multicast address, 224.0.0.1, is handled as a special
> > case. On all systems -- that is all hosts and routers, including
> > multicast routers -- reception of packets destined to the all-systems
> > multicast address, from all sources, is permanently enabled on all
> > interfaces on which multicast reception is supported. No IGMP
> > messages are ever sent regarding the all-systems multicast address.
> >
> > IGMP v2 has something similar:
> >
> > The all-systems group (address 224.0.0.1) is handled as a special
> > case. The host starts in Idle Member state for that group on every
> > interface, never transitions to another state, and never sends a
> > report for that group.
> >
> > But i did not find anything which says all other link-local addresses
> > don't need member reports. Did i miss something?
> >
> > Andrew
>
> From RFC 4541 (Considerations for Internet Group Management Protocol
> (IGMP) and Multicast Listener Discovery (MLD) Snooping Switches):
>
> 2) Packets with a destination IP (DIP) address in the 224.0.0.X range
> which are not IGMP must be forwarded on all ports.
>
> This recommendation is based on the fact that many host systems do
> not send Join IP multicast addresses in this range before sending
> or listening to IP multicast packets. Furthermore, since the
> 224.0.0.X address range is defined as link-local (not to be
> routed), it seems unnecessary to keep the state for each address
> in this range. Additionally, some routers operate in the
> 224.0.0.X address range without issuing IGMP Joins, and these
> applications would break if the switch were to prune them due to
> not having seen a Join Group message from the router.
>
> So, it looks like some hosts and routers out there in the field do not send
> joins for those local addresses. In fact, IPv4 local multicast addresses are
> ignored when Linux bridge multicast snooping adds a new group.
>
> static int br_ip4_multicast_add_group(struct net_bridge *br, ...
> if (ipv4_is_local_multicast(group))
> return 0;
>
> Cascardo.
next prev parent reply other threads:[~2015-08-14 8:55 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-08-12 16:13 [PATCH] IGMP: Inhibit reports for local multicast groups Philip Downey
2015-08-12 23:45 ` David Miller
2015-08-13 14:48 ` Philip Downey
2015-08-13 16:06 ` Andrew Lunn
2015-08-13 16:52 ` Philip Downey
2015-08-13 17:01 ` Andrew Lunn
2015-08-13 18:08 ` Thadeu Lima de Souza Cascardo
2015-08-14 8:55 ` Philip Downey [this message]
2015-08-14 8:56 ` Philip Downey
2015-08-14 13:35 ` Andrew Lunn
2015-08-14 14:36 ` Philip Downey
[not found] <1>
2015-08-24 11:39 ` Philip Downey
2015-08-25 21:20 ` David Miller
2015-08-26 9:23 ` Philip Downey
2015-08-27 15:46 ` Philip Downey
2015-08-28 20:29 ` David Miller
2015-08-28 21:19 ` Cong Wang
2015-08-31 10:33 ` Philip Downey
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