[Bridge] [PATCH net] net: bridge: remove ipv6 zero address check in mcast queries

Nikolay Aleksandrov nikolay at cumulusnetworks.com
Fri Feb 22 11:16:53 UTC 2019

On 22/02/2019 09:57, Hangbin Liu wrote:
> Hi Nikolay,
> On Thu, Feb 21, 2019 at 03:20:14PM +0200, Nikolay Aleksandrov wrote:
>>> Yes, I agree. But this "regression" could be fixed by setting up correct
>>> switch configuration. See more explains below.
>> That is irrelevant, if the setup once worked we should not break it unless
>> it's in RFC requirement violation and RFC 4541 is only suggestive, not required.
> Thanks for your reply. I just noticed the RFC4541 category is informational.
>>> "because this would cause the Queries to be seen as coming from a newly
>>>  elected Querier" means other address could be elected as a Querier but
>>> "" should not.
>> But this change hasn't been incorporated, has it ? A address currently
>> will always win the election and silence all of the rest. Current bridge state
>> is simply broken for some cases because of that.
> Yes. I agree. I realized linus also said
> """
> However, one of the two options seems to be necessary. Either
> reverting the patch for the IGMP part, too. Or Ignoring
> sources for querier eletcion and presence detection.
> """
>> Removing from the election will effectively disable snooping even if there's
>> a configured bridge unless it has an address. You can see that this will end up in
>> people having suddenly their multicast flooded with current setups, right ?
> Yes
>> Any big behaviour change like that should be optional, but I don't think we need 
>> another option as this is not so big of a deal because we're not breaking any
>> required behaviour.
> Just a little curious, RFC 3376 said the General Queries are sent from multicast
> routers. I think a router *should* has a IP address, isn't it?
> RFC 4541 also suggested:
>       If the switch is not the Querier, it should use the 'all-zeros' IP
>       Source Address in these proxy queries (even though some hosts may
>       elect to not process queries with a IP Source Address).
>       When such proxy queries are received, they must not be included in
>       the Querier election process.
> And what I got is most vendors apply this suggestion.
>> In case you decide to follow the option path, please use the new boolopt api to avoid
>> adding new fields to the bridge, this should be an on/off thing. I still vote for a
>> revert though.
> For consistency with other vendors and rfc, I would prefer to remove zero address election.
> For compatibility with previous users, I'm also OK to revert it.
> > Regards
> Hangbin

In this case I'd suggest the following course of action:
 - For -net/-stable revert the change since backporting new options is a
   no-go and we need to restore the bridge state
 - After -net is merged in net-next, for net-next if you'd like add it
   as an option and also exclude it from elections when the option is
   enabled (for example something like multicast_nonzero_src_querier).
   Just please use the boolopt api and don't add new fields/attr ids.
   Obviously by default this option will be off to be backwards
   compatible and avoid surprise mcast flood.

Or just leave it reverted. :)


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