>
>While it might sound theoretically nice to be able to reuse an IID on
>multiple nodes on a single subnet, the operational reality is that it
>will be confusing and never used in practice.
IID uniqueness on a link is an artificial restriction: We don't check
for it with DAD, and not other part of the IPv6 architecture depends
on it. Leaving it in will complicate privacy addresses and some other
situations, and taking it out does not actually require operators to
number their networks in a confusing fashion.
In practice, permanant addresses probably won't have overlapping IIDs.
Autoconfigured addresses will never have overlapping IIDs because there
will always be a corresponding link-local address that is check for
uniqueness with DAD. And, I expect you are correct that operators will
not manually configure multiple nodes on a link to use the same IID.
However, there are two cases where overlapping IIDs may occur:
- Randomly-generated IIDs used for privacy addresses.
To prevent the possibility of overlapping IIDs in
this case, we'd have to generate a link-local
address and perform DAD on it (or some equivalent),
in addition to performing DAD on the privacy address.
- Two separate subnets that are merged onto a single
physical network (due to topology changes, etc.).
If these were manually configured networks, its
likely that both sets of IIDs will include the
same low numbers. However, the original global
and site-local addresses could still be distinguished
by their different subnet IDs, so why require the
IIDs to change?
I don't see any reason why we should keep an artificial restriction
in the addressing architecture that would complicate either of these
cases.
Margaret
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