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[2a10:fc81:a806:d6a9::1]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-466643f4e93sm2703157f8f.7.2026.06.19.15.11.43 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 19 Jun 2026 15:11:43 -0700 (PDT) From: Stefano Brivio To: David Gibson Subject: Re: [PATCH v7 01/13] dhcpv6: Fix reply destination to match client's source address Message-ID: <20260620001142.0d838714@elisabeth> In-Reply-To: References: <20260413005319.3295910-1-jmaloy@redhat.com> <20260413005319.3295910-2-jmaloy@redhat.com> Organization: Red Hat X-Mailer: Claws Mail 4.2.0 (GTK 3.24.49; x86_64-pc-linux-gnu) MIME-Version: 1.0 Date: Sat, 20 Jun 2026 00:11:42 +0200 (CEST) X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: G2ZSQ2iBdLWOZs9hbrZD_IpJaGdfX9gQ9K8irUlebos_1781907104 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-ID-Hash: K66WJXBUVTJXCD433DPVIEYGYIYNWANB X-Message-ID-Hash: K66WJXBUVTJXCD433DPVIEYGYIYNWANB X-MailFrom: sbrivio@redhat.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: Jon Maloy , passt-dev@passt.top X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: On Thu, 14 May 2026 15:21:57 +1000 David Gibson wrote: > On Sun, Apr 12, 2026 at 08:53:07PM -0400, Jon Maloy wrote: > > tap_ip6_daddr() selects the reply destination based on our source > > address type (link-local), so it always returns addr_ll_seen. > > I think there might have been more callers of tap_ip6_daddr() in the > past, which might have made this not true. > > > But if > > the client sent from a global address, we would reply to an address > > different from what the client is expecting. Since RFC 8415 allows > > clients to use global addresses for DHCPv6, we now correct this, and > > always respond to the address the client was using. > > Responding to the same address the client used is a good idea in > general. However, for this specific case, I don't think it will quite > do what we want. The problem is that we're still always using > our_tap_ll (link local) as the source address. So if the client used > a global address we'll send a packet with mismatched address scopes. > AFAIU that won't usually work. At least for TCP on Linux that actually works. I haven't tried DHCPv6. Regardless of that, indeed, it doesn't look like a good idea, and we shouldn't start doing that if we weren't doing it before. -- Stefano