All things related to multicast

[Jeremy George <>]

  I have ongoing first mile concerns about wide ip multicast deployment
within my campus.  We're implementing a pretty common route once,
switch many architecture, so I expect that the issues are not
hopelessly idiosyncratic to Yale.  The major choice we face now in
regard to multicasting is what Layer 2 solution should we adopt as we
pitch hubs in favor of desktop access switches.

  In a spirit of reality-check, are the current issues about as I
detail them below?  And, if there really are a bunch of campuses in a
similar position, could it be worth group (or sub-group) time working
toward a best current practices document?

  At the switch level of a routed/switched environment I see four
basic options to multicast:  treat it as a broadcast, vendor specific
solutions (e.g. cgmp), igmp snooping and mgrp.

  Basically just ignoring multicast and treating it as a broadcast is
probably a blueprint for disaster.  It will work day 1 in simple test
mode but it obviously won't scale.

  CGMP does appear to work from reports I hear, although I've not tried
it.  The problem here isn't necessarily technical but economic.  I
can't imagine that many I2 schools will be willing to lock into any
vendor.

  IGMP snooping seems to me to be almost insidious.  It requires non-
trivial cpu activity from the very device we'd like not to have do
significant computation.  The reason, of course, is that we want to
buy on price point because we'll buy so many.  Given the liklihood that
all of the vendors will shave cost as much as possible, it seems likely that
switches relying on IGMP snooping are primed for byzantine failure at
the worst possible moments, i.e. when they're most wanted and the cpu
overloads.

  GMRP appears to me as though it may be workable.  Either that or I
haven't gotten the word yet.  Among the hooks are that it needs an
802.1p aware NIC.  Is that the general case?  What happens when a
non-aware NIC is attached to the network?  What is the relationship
between gmrp and igmp?  Is there a source for explanation?  CCO seems
to indicate that 12.0(1)T is gmrp capable.  Does igmp go away?  Have
people deployed gmrp in a production environment?

- Jeremy