[rbridge] When would an RBridge say "I don't want layer 2 multicast"?

[Joe Touch]

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Dinesh G Dutt wrote:
> Joe,
> 
> I see your point. I don't know the basis for this requirement. If an
> operator wanted to turn off all non-IP multicast, wouldn't turning on
> this bit be a good idea ? I guess your question is in what situations
> can an operator make this decision. 

Exactly.

> Furthermore, I don't believe
> existing 802.1Q bridges provide such a funtionality. So, maybe getting
> rid of this bit is a good idea as you suggest.
> 
> Let me check with Dino and see if he remembers the need for this bit,

Thanks. That'd be useful.

Joe

> 
> Dinesh
> Joe Touch wrote:
> 
> 
> Dinesh G Dutt wrote:
>  
>>>> There is a L2 protocol called MMRP (used to be called GMRP) that allows
>>>> me to do the equivalent of IGMP but for L2-only multicast (actually it
>>>> can also be used for IP multicast). So, it should be possible for an
>>>> Rbridge to say "don't send me any L2 multicast that isn't derived from
>>>> IP multicast".
>>>>     
> 
> I don't see why these two statements are related. If MMRP can also be
> used for IP multicast or not, then how would an operator ever know when
> to set this bit to "off"?
> 
> I'm suggesting that if we can't give clear advice to an operator on when
> to set each value of a bit, we should not include it.
> 
> Joe
> 
>  
>>>> James Carlson wrote:
>>>>  
>>>>    
>>>>>>> Joe Touch writes:
>>>>>>>             
>>>>>>>> Donald Eastlake wrote:
>>>>>>>>                 
>>>>>>>>> This was put
>>>>>>>>> through a consensus call on the working group mailing list
>>>>>>>>> resulting
>>>>>>>>> in the formal consensus determination here:
>>>>>>>>> http://www.postel.org/pipermail/rbridge/2007-September/002470.html.
>>>>>>>>>                       
>>>>>>>> Besides your mail, there was only one post from James Carlson
>>>>>>>> endorsing
>>>>>>>> the idea:
>>>>>>>> http://www.postel.org/pipermail/rbridge/2007-July/002400.html
>>>>>>>>                   
>>>>>>> Just to make clear (which itself might be impossible at this point):
>>>>>>> the reason I supported it was for symmetry with the other multicast-
>>>>>>> optimizing bits already defined.  If the implementation has some
>>>>>>> reason to know that it has useful local information about non-IP
>>>>>>> multicasts in use (e.g., the subnet in question runs only IP or
>>>>>>> perhaps is known to use GMRP for all multicast addresses), then it
>>>>>>> can
>>>>>>> set or reset the flag as needed.  If it doesn't (or can't) know about
>>>>>>> non-IP multicast usage, then it should set it to 1 with the rest of
>>>>>>> those who aren't snooping the multicast control protocols.
>>>>>>>
>>>>>>> I somewhat doubt it's going to see much use, but it's also fairly
>>>>>>> cheap -- as long as we already have to support IPv4 and IPv6 control
>>>>>>> bits.  (And since, if you're lazy, you can just ignore it and let the
>>>>>>> downstream discard the unwanted packets.)
>>>>>>>               
>>>> I'm seeing a "something operators can set as desired", but not a reason
>>>> they would ever want to set it. I particularly dislike the idea of
>>>> filtering multicasts based on upper layer info (i.e., whether it's IP or
>>>> not). IGMP is an optimization, but it seems like this bit could break
>>>> things when its use wasn't needed - and I still don't see a clear need.
>>>>
>>>> Joe
>>>>     
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>  
>>

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