All things related to multicast

[Matthew Davy <>]

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On May 30, 2006, at 1:59 PM, Bill Owens wrote:

> On Tue, May 30, 2006 at 01:11:55PM -0400, Matthew Davy wrote:
> > So based on http://www.iana.org/assignments/multicast-addresses,
> > which seems to be the authoritative source of multicast address
> > assignment, the IANA reserved space is:
> >
> > 224.1.0.0 - 224.1.0.37  Reserved                            [IANA]
> > 224.1.0.39 - 224.1.0.255 Reserved                           [IANA]
> > 224.1.5.0 - 224.1.255.255 Reserved                          [IANA]
> > 224.3.0.64 - 224.3.255.255     Reserved                        [IANA]
> > 224.5.0.0 - 224.251.255.255  Reserved                          [IANA]
> > 225.0.0.0 - 231.255.255.255 Reserved                 [IANA]
> > 234.0.0.0 - 238.255.255.255 Reserved                     [IANA]
>
> A quick count, we have 2739 MSDP SAs in our NYC router just now,  
> and about 690 of them would be blocked by this filter. I have no  
> idea whether they are in the table because of unintentional  
> leakage, or stupid application writers, or perhaps are actually  
> being used. The largest single group in the reserved range is  
> 234.21.81.1 has 271 sources, and is used by LimeWire. Of course,  
> the largest group is 'legit' in that it has been approved by IANA,  
> but probably shouldn't be getting out to the world; 224.1.0.38  
> (that's Retrospect, the backup software, to save everyone from  
> having to look). 313 sources. And our old friend 224.0.1.76, the  
> IAPP group, is hanging in there with 111 access points chiming away.

Thanks for the quick analysis !    This would clearly block a lot of  
SAs that are being accepted today.   I wonder if users have gotten  
used to just picking a group randomly out of the vast reserved space  
and using it instead of using GLOP or SAP or SSM   ?    If so, this  
is a behavior that should probably change.   But the question is,  
what we would we break if we implemented this filter ?


> > IMO this is definitely the "right thing" to do (regardless of the
> > benefits) and would go a long way to accomplishing all the potential
> > goals that Bill Owens mentioned.
>
> I wasn't advocating for those goals; I was listing them as a  
> question for the group, to try to ascertain goal or goals we're  
> aiming at.

Sorry, I didn't mean to indicate you were advocating those.   Just  
noting that is would accomplish the goals of protecting various  
things - if those were goals people were interested in.

- - Matt

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