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[67.216.200.102]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-1903a275026sm19890469c88.5.2026.10.22.02.17.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 22 Oct 2026 02:17:42 -0700 (PDT) From: Cheng Yongkang To: Andrew Lunn Cc: "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [BUG] net: ipvlan: ambiguous external multicast frame is dropped Date: Thu, 22 Oct 2026 02:17:36 -0700 Message-Id: <20261022091736.3652981-1-teel4res@gmail.com> X-Mailer: git-send-email 2.34.1 X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Hi all, ipvlan_external_frame() classifies an ingress multicast frame as local when its Ethernet source equals the shared ipvlan parent/slave MAC and its L3 source is present in the port-wide address hash. An external sender can produce the same tuple. The frame is then returned with RX_HANDLER_PASS and is not queued to any L2 ipvlan slave. Observed on Linux v7.3, commit 08ab31164c55f20c7a2653de3186ae333470e2c1, with two ipvlan L2 slaves and a veth peer acting as the external sender: external ARP broadcast, source MAC == ipvlan MAC, sender address configured on a slave: parent RX +1 slave 0 RX +0 slave 1 RX +0 identical frame with a different sender MAC: parent RX +1 slave 0 RX +1 slave 1 RX +1 Packet-socket marker captures agreed with the RX counters. The frame is lost only when the ambiguous source tuple is used. The macvlan sibling documents that source-MAC ambiguity cannot be resolved and prefers delivery, accepting possible duplicates. ipvlan currently chooses the opposite behavior and can cause packet loss. The same classifier also explains the duplicate direction in candidate BR-015 when a reflected local frame has an address that is not in the port hash. The classifier should use an unambiguous local-origin indication or make the ambiguity policy consistent with macvlan. Candidate BR-016 is canonical because packet loss is the more important symptom. The self-checking reproducer and complete console log are available on request. This was found with a multi-agent workflow; the packet delivery differential was reproduced in QEMU. Thanks, Cheng Yongkang