IPv6 duplicate address detection

[JINMEI Tatuya / 神明達哉]

At Wed, 06 May 2009 15:49:45 -0700,
Bob Van Zant <bob at veznat.com> wrote:

> > I'm afraid we need clarification first...what do you mean by
> > "reconfigure an interface with an IPv6 address"?  Do you mean adding a
> > new IPv6 address to an interface?  If so, I'm not sure why you
> > referred to the following part of RFC2461 (btw the RFC was updated by
> > RFC4861):

> We have a crude form of NIC pairing in our software. We allow someone to
> logically pair two interfaces together. This is implemented by `ifconfig
> down` both interfaces, configure them both the same, then `ifconfig up` the
> primary interface. We then monitor the link state of the primary interface.
> If the state goes to down, we `ifconfig down` the primary NIC and then
> `ifconfig up` the secondary NIC. This has the effect of changing the link
> layer address associated with a given IPv6 address. After we do this we send
> out the unsolicited NA to update whatever switch we're plugged into.

Okay, thanks for the explanation.  But I still don't understand one
thing: why is DAD triggered for the address on the secondary NIC?
Unless someone has changed the code recently, the FreeBSD
(KAME-derived) IPv6 stack shouldn't trigger DAD for an existing
address simply because the interface becomes 'up' (this behavior may
be debatable per se, but that's a different question).  Did you
perhaps make the address "tentative" by hand after configuring the
address?

---
JINMEI, Tatuya
Internet Systems Consortium, Inc.