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[204.195.96.226]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-11b060885cdsm11887379c88.6.2025.11.14.09.03.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 14 Nov 2025 09:03:46 -0800 (PST) Date: Fri, 14 Nov 2025 09:03:41 -0800 From: Stephen Hemminger To: "Robin Jarry" Cc: Morten =?UTF-8?B?QnLDuHJ1cA==?= , , "Christophe Fontaine" , Subject: Re: [PATCH dpdk] net: ipv6 link local compliance with rfc 4291 Message-ID: <20251114090341.589bcbd6@phoenix> In-Reply-To: References: <20251114105751.54802-3-rjarry@redhat.com> <20251114080532.1e86d13e@phoenix> <98CBD80474FA8B44BF855DF32C47DC35F65560@smartserver.smartshare.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org On Fri, 14 Nov 2025 17:46:42 +0100 "Robin Jarry" wrote: > Morten Br=C3=B8rup, Nov 14, 2025 at 17:14: > >> From: Stephen Hemminger [mailto:stephen@networkplumber.org] > >> Reading the kernel source there is also special handling to include > >> device > >> id into link local address. This is to handle corner case where > >> multiple network > >> cards have same hardware MAC address. =20 > > > > Multiple physical NICs should never have the same MAC address. > > Lots of stuff will break if they do. > > E.g. a network switch will forward packets to the NIC that most recentl= y sent packets, so its MAC address was learned in the MAC address table in = the switch. > > > > What is the use case justifying this tweak in the kernel? =20 >=20 > Some drivers expose multiple ports sharing the same mac address. >=20 > This very is specific to certain hardware vendors. The comment here > refers to a change from 2005. I couldn't find the root commit/email. Yes, this code is in first git commit 2.6.12 from 2005 it is possible (but not worth the effort) to find it in earlier repos.