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

Thadeu Lima de Souza Cascardo cascardo at redhat.com
Mon Oct 3 22:41:50 UTC 2016


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
> 
> > _______________________________________________
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> > discuss at openvswitch.org
> > http://openvswitch.org/mailman/listinfo/discuss
> 
> 
> 
>    



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