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

[my_ovs_discuss at yahoo.com]

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


 

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      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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