[G'day Eric, thanks for your input ...]
On 2004-06-01, Erik Nordmark wrote:
> [Pekka Savola wrote:]
> >
> > 1) The draft specifies that instead of using a tentative address as the
> > source address for RS, another address or the unspecified address should be
> > used instead. To me, using the unspecified address would seem shortsighted,
> > so I'd like to disallow its use in this context. (This might cause a
> > problem, though, because I don't think the nodes typically have an another
> > address they can use...)
>
> But RFC 2461 explicitly allows sending RS with an unspecified source.
> Is there a bug in RFC 2461 in this area?
I don't think it's a bug ...
"A router MAY choose to unicast the response directly to
the soliciting host's address (if the solicitation's
source address is not the unspecified address), but the
usual case is to multicast the response to the all-nodes
group" [RFC2461 6.2.6]
... it's a feature, asking the router "please be sure to
broadcast the response back to me since I don't have an address
I'm sure of yet".
The only problem there is the rate-limiting imposed on the
multicast responses, but I think we can assume that access
routers for fast mobile networks will have MinRtrAdvInterval
and related 2461 variables tweaked appropriately and some of
the other rules bent ... and I think that's MipSHOp WG's problem,
not IPv6 WG's problem ...
(I'm probably going to disallow RSes from Optimistic addresses
entirely, so if we don't have any other addresses we'll _have_
to RS from unspecified. The current draft tries to get around
this with some tricks, but they tickle weird features of 2461,
I think ... see the last sentence of 6.2.6)
...
> > What might be useful is specifying with which kind of addresses
> > oDAD should be assumed: [...] Manual addresses or DHCPv6 in
> > particular should be disallowed.
>
> [...]
> But is also isn't clear to me that the probability, even in the
> manual case, is high enough to warrant pessimistic mode.
I (personally) tend to agree, but I (editorially) am trying to steer
a course between paranoia and recklessness :-)
>From Pekka's comments, section 3.3 should be removed, and as Pascal
Thubert pointed out in an earlier review, it's not always obvious
whether an address is 'really' manual when we're configuring it.
So this bit of the text definitely needs an overhaul.
> But if the probability of collisions is 10% let alone 1% (the
> latter might be a guess at collision probability for manually
> configured addresses) why do we think it would be bad to operate
> in optimistic mode?
Yeah, I wanted to come up with a limiting number for this, but
stumbled on the problem of estimating the costs in a sensible
way. All offers of help gladly received!
-----Nick
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