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Date:      Sun, 2 Mar 2025 13:23:16 +0100
From:      A FreeBSD User <freebsd@walstatt-de.de>
To:        freebsd-net@freebsd.org
Subject:   mpd5: How to prevent tun0 getting multiple valid IPv6 addresses?
Message-ID:  <20250302132343.6b50b4aa@thor.sb211.local>

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Hello,

Router/Firewall host is running FreeBSD 14-STABLE:
FreeBSD 14.2-STABLE #20 n270632-859aa726fb86: Fri Feb 28 19:38:05 CET 2025

I'm using mpd5(8) to connect to our ISP via vDSL. Utilizing an appropriate =
"link-up.sh"
script, which effectively does

- restart rtsol on tun0 (rtsol tun0 &)
- restart dhcp6c (service dhcp6 restrt)
- doing some logging
- performing some DDNS adjustments with the appropriate provider

mpd5 is configured to obtain IPv4 and IPv6 via ipcp, ipv6cp.

While IPv4 has never been a problem, it seems that IPv6 is stuck with SLAAC=
 (I never managed
to obtain an IPv6 via DHCP (dhcp6c(8) from ports), always EUI64, privacy mo=
de set).

Restarting mpd5 provides only ONE valid IPv6 address on tun0.

When ISP is resetting the address assignment usually after 24 hours for bot=
h IPv4 and IPv6, I
end up very often having at least two or even more, still valid IPv6 addres=
ses (meaning: none
of the former assigned IPv6 addresses is marked deprecated or invalid). Thi=
s renders DDNS
useless, since I have no plan how to figure out the valid address.

This problem occured recently, I do not know what causes it, I guess it cam=
e with a recent
STABLE upgrade.=20

How can mpd5 be forced to deprecate an address before obtaining a new one? =
How to finde out
which of the assigned IPv6 addresses is the "old" one and mark it deprecate=
d? I run a simple
script searching for "tentative, deprecate and so on" addresses to leave th=
e good one(s) when
providing my DDNS provider with the mutually correct IPv6 address of mine.

Utilising link-down.sh of mpd5(8) seems a good place to eradicate IPv6 addr=
esses (by filtering
out fe80:: or mutually assigned ULA, leaving the valid IPv6 for deletion), =
but this seems
non-conformal to me.

A bug or a "feature"?

Thanks in advance,

Oliver


--=20

A FreeBSD user

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