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[2a10:fc81:a806:d6a9::1]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4909c1035ebsm104407205e9.5.2026.06.01.01.08.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 01 Jun 2026 01:08:28 -0700 (PDT) From: Stefano Brivio To: Tj Cc: =?UTF-8?B?w43DsWlnbw==?= Huguet , Thorsten Leemhuis , Fernando Fernandez Mancera , Jakub Kicinski , netdev@vger.kernel.org, Yumei Huang , Ido Schimmel , Justin Iurman , David Ahern , David Gibson , Linux kernel regressions list , Beniamino Galvani Subject: Re: Problem with IPv6 privacy addresses in 7.0 Message-ID: <20260601100826.4222a657@elisabeth> In-Reply-To: <3f0d5431-60b0-42dc-8192-2f8a3c6da50e@proton.me> References: <20260529220415.22d0be8d@elisabeth> <3f0d5431-60b0-42dc-8192-2f8a3c6da50e@proton.me> Organization: Red Hat X-Mailer: Claws Mail 4.2.0 (GTK 3.24.49; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Date: Mon, 01 Jun 2026 10:08:27 +0200 (CEST) On Fri, 29 May 2026 20:18:55 +0000 Tj wrote: > On 29/05/2026 20:04, Stefano Brivio wrote: > > On Fri, 29 May 2026 18:28:58 +0000 > > Tj wrote: > > > >> I believe I hit this on a router using Debian 13 with v7.0.* kernel this week that > >> uses systemd-networkd to configure IPV6 RA and prefix delegation after > >> moving from v6.19.*. > >> > >> Symptom was the router could no longer reach public IPv6 addresses > >> itself but forwarding was unaffected. > >> > >> The ISP (Starlink) provides a /64 prefix via RA and a /56 via DHCPv6. networkd > >> allocates a static suffix address from both to the WAN-side interface. > >> > >> I discovered after much experimentation that instead of the usual /56 > >> address being the source it was choosing the /64 and failing. > > Do you really mean an address configured as /56, or a /64 address that > > systemd-networkd derives from a /56 delegated prefix? > > Apologies - I should have been clearer. I meant addresses generated > *from the* respective prefixes - the addresses themselves are /64, yes! Thanks for clarifying. Meanwhile, Jakub applied Fernando's revert patch (I'm actually relieved, thanks Jakub ;)) but I had a look anyway into how systemd-networkd handles these two cases. They both seem to be hitting in the same way configure_address() (src/network/networkd-address.c) with no attempt to define a given order. After all, the only way to force a specific order would be to remove and add addresses back, which systemd-networkd doesn't do. So, whether the setup worked before the patch (and after the revert) depends on the order of events / configurations, which in some sense makes it even more important that we keep a stable order by default. Contrary to NetworkManager, here, there's nothing we could really "fix". -- Stefano