All things related to multicast

[Leonard Giuliano <>]

On Mon, 29 May 2006, Stig Venaas wrote:

-) 
-) In general I wouldn't recommend blocking reserved space. It makes it very
-) hard for some of the space to become un-reserved in the future if you see
-) what I mean. If at some point some of this space should be unblocked, it
-) might be hard to get everyone to open up.
-) 

Any new allocations are generally done in 224/8 right now.  At this time, 
there do not appear to be any promising mechanisms that would consume any 
mcast addresses outside of 224/8, 232/8 or 233/8.  So just a quick and 
dirty 3-line policy might be to allow 224/8, 232/8 and 233/8 and block 
everything else from global/interdomain forwarding would get rid of 
13/16's of the random attacks (worms, etc).  Given the very low 
probability that any addresses in 225/8-231/8, 234/8-239/8 will be 
assigned for global use anytime soon, compared with the large 
vulnerability target they currently provide, it seems like benefits 
strongly outweigh the potential dangers of filtering.


-Lenny