[ovs-discuss] openvswitch-2.5.0 IGMP-SNOOPING question

Fri Oct 28 01:25:42 UTC 2016

On Fri, Oct 28, 2016 at 12:16:23AM +0000, my_ovs_discuss at yahoo.com wrote:
> It is not just about forwarding mcast traffic to linux bridge querier.If we don't consider this 0.0.0.0 source IP IGMP query, then host entries will time out and traffic to mcast receiver will stop.Even though the linux bridge querier is querying, we are ignoring it.
> Either we should consider 0.0.0.0 source IP querier as querier and add it to our table orat least forward that query in the VLAN so that query reaches the receivers and they will respond, which keeps the hosts in the table and traffic wouldn't get disturbed.
> -Thanks,
>  

So, you need a querier from OVS as well, or another querier on the system. Using
the Linux bridge querier as a way of enforcing hosts to keep sending their
reports does not warrant us breaking protocol.

The queries are forwarded, it's the membership reports that are not. If you add
a proper router querier to the system, one which does not use the source address
0.0.0.0, things might work as you expect.

Another thing you can do is match the timeouts with the report intervals from
the hosts in such a way that entries won't time out before the reports are due.
Or you can set flood_unreg option
(other-config:mcast-snooping-disable-flood-unregistered=false).

Cascardo.

> 
> 
>       From: Thadeu Lima de Souza Cascardo <cascardo at redhat.com>
>  To: my_ovs_discuss at yahoo.com 
> Cc: Discuss <discuss at openvswitch.org>
>  Sent: Thursday, October 27, 2016 4:49 PM
>  Subject: Re: [ovs-discuss] openvswitch-2.5.0 IGMP-SNOOPING question
>    
> On Thu, Oct 27, 2016 at 10:03:37PM +0000, my_ovs_discuss at yahoo.com wrote:
> > Haven't gotten any response for this so far.
> >  
> > 
> 
> As I responded before, a switch querier using IP address 0.0.0.0 is not a
> router, and should not be considered as such. So, given your topology, the
> correct behavior is OVS sending the traffic from the multicast source to the
> multicast receiver. With multicast snooping on, the port connected to the Linux
> bridge with bridge querier active should not receive the multicast traffic meant
> for the multicast receiver. Do you observe a different behavior? What exactly do
> you want to do?
> 
> Regards.
> Thadeu Cascardo.
> 
> > Sent from Yahoo Mail. Get the app
> > 
> >      From: "my_ovs_discuss at yahoo.com" <my_ovs_discuss at yahoo.com>
> >  To: Thadeu Lima de Souza Cascardo <cascardo at redhat.com> 
> > Cc: Discuss <discuss at openvswitch.org>
> >  Sent: Monday, October 3, 2016 3:56 PM
> >  Subject: Re: [ovs-discuss] openvswitch-2.5.0 IGMP-SNOOPING question
> >    
> > Yes, Linux bridge querier.
> > Topology is attached in the pdf.
> > -Thanks.
> > 
> > 
> >  
> > 
> > Sent from Yahoo Mail. Get the app
> > 
> >      From: Thadeu Lima de Souza Cascardo <cascardo at redhat.com>
> >  To: my_ovs_discuss at yahoo.com 
> > Cc: Discuss <discuss at openvswitch.org>
> >  Sent: Monday, October 3, 2016 3:41 PM
> >  Subject: Re: [ovs-discuss] openvswitch-2.5.0 IGMP-SNOOPING question
> >  
> > On Mon, Oct 03, 2016 at 09:17:00PM +0000, my_ovs_discuss at yahoo.com wrote:
> > > Thanks Cascardo for the response.
> > > The problem is IGMP querier in Linux kernel sends queries with source IP 0.0.0.0 and this is being ignored by OVS.Since the current implementation of mcast-snooping in OVS isn't really tracking the source IP of queriers, can we relax this source IP 0.0.0.0check for queries?
> > > Thanks
> > > 
> > 
> > Do you mean the Linux bridge querier? What is your topology? Do you want OVS to
> > forward the queries from Linux bridge or something like that?
> > 
> > Cascardo.
> > 
> > > 
> > >  
> > > 
> > > Sent from Yahoo Mail. Get the app
> > > 
> > >      From: Thadeu Lima de Souza Cascardo <cascardo at redhat.com>
> > >  To: my_ovs_discuss at yahoo.com 
> > > Cc: Discuss <discuss at openvswitch.org>
> > >  Sent: Monday, October 3, 2016 7:20 AM
> > >  Subject: Re: [ovs-discuss] openvswitch-2.5.0 IGMP-SNOOPING question
> > >    
> > > On Fri, Sep 30, 2016 at 01:25:08AM +0000, my_ovs_discuss at yahoo.com wrote:
> > > > Hi,  openvswitch-2.5.0 seems to ignore IGMP queries with source IP 0.0.0.0
> > > > But, RFC seems to say the following: Highlighted in red.
> > > > That switches shouldn't drop queries with source IP 0.0.0.0.
> > > 
> > > The highlighted section mentions IGMP *MEMBERSHIP REPORTS*, not queries. That
> > > section refers to switches that implement proxy reporting, which OVS doesn't.
> > > OVS, however, does not add to the list of multicast routers the ports where IGMP
> > > queries with source address 0.0.0.0 arrives (unless queries with other source
> > > addresses arrive, that is). That is in complicance with this same quote, see
> > > item B below.
> > > 
> > > Did you mean that queries with source address 0.0.0.0 are not forwarded? In that
> > > case, OVS will look at the destination address and send only to those ports that
> > > belong to that multicast group. If it's a membership report, OVS will send only
> > > to ports belonging to multicast routers.
> > > 
> > > Does this behavior you see cause any real problem? Like some multicast traffic
> > > not reaching some destinations?
> > > 
> > > Regards.
> > > Cascardo.
> > > 
> > > > 
> > > > RFC 4541    IGMP and MLD Snooping Switches Considerations      May 2006
> > > > 
> > > > 
> > > >      This is not a problem in an IGMPv3-only network because there is
> > > >      no suppression of IGMP Membership reports.
> > > > 
> > > >      The administrative control allows IGMP Membership Report messages
> > > >      to be processed by network monitoring equipment such as packet
> > > >      analyzers or port replicators.
> > > > 
> > > >      The switch supporting IGMP snooping must maintain a list of
> > > >      multicast routers and the ports on which they are attached.  This
> > > >      list can be constructed in any combination of the following ways:
> > > > 
> > > >      a) This list should be built by the snooping switch sending
> > > >          Multicast Router Solicitation messages as described in IGMP
> > > >          Multicast Router Discovery [MRDISC].  It may also snoop
> > > >          Multicast Router Advertisement messages sent by and to other
> > > >          nodes.
> > > > 
> > > >      b) The arrival port for IGMP Queries (sent by multicast routers)
> > > >          where the source address is not 0.0.0.0.
> > > > 
> > > >          The 0.0.0.0 address represents a special case where the switch
> > > >          is proxying IGMP Queries for faster network convergence, but is
> > > >          not itself the Querier.  The switch does not use its own IP
> > > >          address (even if it has one), because this would cause the
> > > >          Queries to be seen as coming from a newly elected Querier.  The
> > > >          0.0.0.0 address is used to indicate that the Query packets are
> > > >          NOT from a multicast router.
> > > > 
> > > >      c) Ports explicitly configured by management to be IGMP-forwarding
> > > >          ports, in addition to or instead of any of the above methods to
> > > >          detect router ports.
> > > > 
> > > >    2) IGMP networks may also include devices that implement "proxy-
> > > >      reporting", in which reports received from downstream hosts are
> > > >      summarized and used to build internal membership states.  Such
> > > >      proxy-reporting devices may use the all-zeros IP Source-Address
> > > >      when forwarding any summarized reports upstream.  For this reason,
> > > >      IGMP membership reports received by the snooping switch must not
> > > >      be rejected because the source IP address is set to 0.0.0.0. 
> > > > 
> > > > -Thanks
> > > 
> > > > _______________________________________________
> > > > discuss mailing list
> > > > discuss at openvswitch.org
> > > > http://openvswitch.org/mailman/listinfo/discuss
> > > 
> > > 
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