[DNA] when to rerun DAD

[Thomas Narten <narten@us.ibm.com>]

JinHyeock Choi <jinchoe@gmail.com> writes:

> > Some key questions for DNA.
> >
> > 1) when reusing "old" config, do we need to do anything special? E.g.,
> >   change state of ND entries to STALE? Put addresses in Optimistic
> >   state? Take into account how much time has elapsed since we were
> >   last attached (or just assume this happens as part of normal ND
> >   timers?)
> >
> >   What harm can occur from continuing to use the same information?
> >   how does this compare with the harm of delaying the configuration
> >   of an interface until one is more certain?

> It may cause address conflict if a host continues to use the existing
> 'IP address' without DAD. While the host is away from the link, it's
> possible that another node happens to configure the host's IP address,
> because there was nobody to defend the address.

IMO, we may want to think about having a separate discussion about
"when to run DAD". The blanket "rerun DAD at all times there is some
doubt" strikes me as overkill. For example, why rerun DAD if one has
been disconnected only 10 seconds? or 30? Maybe we should if we've
been disconnected for an hour (but then, do we need to bother with
DNA?).  Also, why rerun DAD if one has generated an address using the
IEEE Identifier (and one has run DAD on it before)? That is, different
types of addresses have different "probability of possible collision"
risks in terms of other hosts attempting to use such addresses.

Thomas