All things related to multicast

[Stig Venaas <>]

Bharat Joshi wrote:
> Hi Stig,
>
>     Thanks for responding to this query. Please see in line.
>
> > > > > * Do existing IGMPv3 capable applications support Exclude mode for ASM
> > > > > groups?
> > > > I don't think so.
> > > Ok. So most of the times, applications will use one or multiple source 
> > > addresses for ASM groups in INCLUDE mode.
> > >
> > > > > * Also do anyone see a need for EXCUDE mode to be supported for their
> > > > > existing applications or any new applications they will create or like
> > > > > to use?
> > > > I don't think there is necessity to use EXCLUDE mode for general
> > > > multicast applications, except some service discovery protocols, which
> > > > usually use (*,G). In other words, no use with source specific EXCLUDE
> > > > mode join/leave.
> > > So EXCLUDE mode is typically used to allow all and never with a source list.
> > While I don't know any applications, it might be useful for say
> > conferencing to exclude sources for muted participants.
>
> Ok.
>
> I am looking for such cases where it may be useful and till now I could
> not find any application using it.

Right. That doesn't mean it isn't useful, or that applications will not
use it in the future though. There are not many SSM applications yet
either... The API is not available on that many platforms and many
developers don't know how to use it. I would rather try to see if the
theoretical uses are so important that we want to keep the complexity,
or if it's not worth it...

> The biggest issue I see is that if someone uses EXCLUDE mode, though he
> might be able to avoid traffic from some specific individual but with
> this he might start getting unwanted traffic from all others which he
> did not even know existed.

For some applications it is easier to use ASM than to try to detect
sources out of band... Not very secure, but it is kind of sufficient
today. Perhaps if you could also exclude anyone misbehaving...

Anyway, SSM is probably the way to go...

Stig

> Regards,
> Bharat
>
> > Stig
> >
> > > > >      I just wanted to know on how much this complex functionality
> > > > > ['Exclude Mode support'] being used in the field?
> > > > I cannot imagine it'll be needed.
> > > >
> > > > In fact, eliminating EXCLUDE (S,G) join/leave is "beneficial" for
> > > > multicast communications. For example, it reduces host/router/switch
> > > > implementation costs and routing tree maintenance costs. It's not just
> > > > "unneeded". This is my thought.
> > > Ok. I am also of the same opinion.
> > >
> > > So with above assumptions, it looks like an IGMPv3 host/router part 
> > > implementation or IGMPv3 snooping which does not handle EXCLUDE with source 
> > > list should be able to work in multicast networks.
> > >
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