Multicast traffic % in enterprise network ?

Thomas Bellman bellman at
Thu Aug 9 08:33:54 UTC 2018

On 2018-08-08 23:36, nanog at wrote:

> Let me fix that for you.
> Using multicast on IPv6 grant us the ability to do more.
> Today, this is worthless.
> Will it be the same tomorrow ?

Problem is, to handle the Neigbour Discovery design (16M multicast
groups), we need hardware that does not exist yet, is unlikely to
exist for at least another decade and will not be down to reasonable
prices (< 5 kUSD) for even longer.  In the meantime, IPv6 neigbour
discovery *precludes* the use of multicast for other purposes on
non-small networks, because IPv6 ND will use up all multicast groups.

If ND had limited itself to 256 multicast groups, it wouldn't have
been a problem.

> Multicast without NDP is broadcast,

(With s/NDP/MLD/ as you yourself mentioned.)

That's the case for Ethernet.  Hop over to the Infiniband or OmniPath
world, and multicast without MLD will cause packets to be dropped.
There is no such thing as broadcast on IB or OPA.

(At least OmniPath does have something called "multicast LID sharing",
where the IPv6 ND groups are clamped down to just 512 distinct groups,
but I haven't read up on the details for how that works, yet.  I don't
know offhand if there is something similar for Infiniband.)


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