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Date:      Sun, 2 Nov 2003 15:03:24 +0100 (CET)
From:      Barry Bouwsma <freebsd-misuser@remove-NOSPAM-to-reply.NOSPAM.dyndns.dk>
To:        FreeBSD Networking Nerds <freebsd-net@freebsd.org>
Subject:   IPv6 autoconf addresses with changing RAs...
Message-ID:  <200311021403.hA2E3OE48213@NOSPAM.spam.NOSPAM.spam.NOSPAM.dyndns.dk>

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[Drop hostname part of IPv6-only address above to obtain IPv4-capable e-mail,
 or just drop me from the recipients and I'll catch up from the archives,
 since I'm too much offline and replies will probably go astray anyways]


Apologies if this has been asked before; I've only zgrep'ed this year's
archives for `autoconf' and see nothing comparable -- only something
from beginning-October-or-so concerning autoconf IPv6 addresses learned
from multiple routers -- a setup which I don't want any so-called `solution'
to my query to adversely affect.

I have one IPv6 machine behind a second, which second machine for
historical reasons has an IPv6 prefix/address that occasionally changes.
After this happens, the first host-only machine receives an additional
autoconf IPv6 address, but it still retains the old (now obsolete) IPv6
autoconf address it had learned from this same router.  The machines are
running kernels RELENG_4 from late-September-ish.  Userland varies horribly.

What I want to happen, is that when the new IPv6 address is autoconf'ed,
the old one should disappear from the interface.  (I've been too impatient
to watch if it disappears after time, during which time I cannot reach
the router's new address or the default route, as the old prefix which
it had is no longer present thanks to my hacked scripts.  If I manually
delete the original IPv6 address, it seems that things work.)


[Historical reasons background:  I receive a different IPv4 address via
dial-in PPP each time I go online.  From this I derive a 6to4 2002:...
prefix that I use for IPv6 network address.  The router machine (the ppp
machine) is poked to deliver an RA at time of new address configuration.
I no longer bother to delete this 6to4 address when going offline, but
next time I go online, I get a new IPv6 prefix (deleting the old one),
that the host machine learns.]

Is there a way of being automagically notified when a RA is heard/a new
IPv6 address is autoconf'ed, so I can trigger a script to check and if
needed, delete the old IPv6 address?  Or must I periodically check the
IPv6 addresses for any changes?

Or, is it possible for the kernel itself, in my case -- a single router,
to be different from the case posted a month ago of two routers on the
same net -- to automagically dispose of the old previously-autoconf'ed
IPv6 address upon receiving a new RA broadcast?  Perhaps to be controlled
by a sysctl knob, to allow one to choose between a single changing RA, or
RAs from multiple machines where IPv6 address-hopping is unwanted?

The advantage of being notified of such an RA change (instead of it just
resulting quietly in an IPv6 address change) is that I could at the same
time trigger a dynamic DNS update.  At present, it seems I need to do
both IPv6 address fudging and dynamic DNS updates with periodic polling
of the interface status.


Thanks,
Barry Bouwsma
still unclear on the concept



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