A few days ago, I integrated the Multicast 3.5 distribution from PARC
into NetBSD-current.  Among other things, Multicast 3.5 includes
pruning DVMRP, which allows you to drastically reduce the amount of
MBONE traffic you get.

Jason Thorpe and I have also done some work to clean up some of this
code, and in particular I've fixed several bugs in the kernel-side
implementation and reduced its size significantly.  The lot appears to
be fairly stable now.

This code is likely to undergo some more changes in the near future,
but this shouldn't adversely affect its stability.

If you have any problems with it, let us know.