On Nov 10, 2009, at 10:29, Kris Pister wrote:
Carsten Bormann wrote:
Please do show me the mesh that has an efficient mostly-reliable
subnet-wide multicast.
Carsten - how do you define efficient and mostly-reliable? With
15.4E you get something north of 98% reliable subnet-wide multicast
with a single transmission from each routing node. Is that good
enough, or is the very act of flooding the subnet objectionable?
I don't know whether it is objectionable, but it may not be very
efficient to send all DAD messages to every node.
(It certainly limits scalability.)
that DAD is necessary,
Ah, good, let's discuss that! If we don't need DAD, we don't need
half of ND.
Leaving things out is always the best way to design things.
However, we wanted to be functionally compatible with ND.
[...]
I didn't understand the reasons presented why we need DAD. The last
I remember was "there might be counterfeit nodes that have the same
MAC EUID". That particular argument doesn't make any sense to me,
but I may have missed others that make more sense.
That depends.
When we still said that the IPv6 address was hardwired to the EUI-64,
the only concern was duplicate EUI-64s.
How do these happen?
1) manufacturing errors. This has happened often enough in Ethernet
space that DAD was made mandatory in 4861.
2) counterfeiting. Counterfeiters have a strong interest to make
their products look a lot like the real thing, and for that very
reason can't coordinate EUI-64 space usage with the real vendor, so it
is quite likely that they will hit the same EUI-64s. Is that a
problem? In the network element space, counterfeiting of expensive
equipment (e.g., made by Cisco) is a very real one.
Since -07, we now explicitly allow non-EUI-64-based addresses, so
these definitely need DAD (currently both groups are treated
identically).
Again, entirely getting rid of a function is always the best
optimization.
Can we do that for DAD?
Gruesse, Carsten
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