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([2a01:e0a:b41:c160:6a1d:efff:fe52:1959]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-42b53e7b12asm32897630f8f.10.2025.11.18.08.41.14 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 18 Nov 2025 08:41:14 -0800 (PST) Message-ID: Date: Tue, 18 Nov 2025 17:41:14 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: nicolas.dichtel@6wind.com Subject: Re: [PATCH] net/ipv6: allow device-only routes via the multipath API To: David Ahern , azey Cc: "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , netdev , linux-kernel References: <7a4ebf5d-1815-44b6-bf77-bc7b32f39984@kernel.org> <19a969f919b.facf84276222.4894043454892645830@azey.net> From: Nicolas Dichtel Content-Language: en-US Organization: 6WIND In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Le 18/11/2025 à 17:04, David Ahern a écrit : > On 11/18/25 4:00 AM, azey wrote: >> On 2025-11-18 10:05:55, +0100 Nicolas Dichtel wrote: >>> If I remember well, it was to avoid merging connected routes to ECMP routes. >>> For example, fe80:: but also if two interfaces have an address in the same >>> prefix. With the current code, the last route will always be used. With this >>> patch, packets will be distributed across the two interfaces, right? >>> If yes, it may cause regression on some setups. >> >> Thanks! Yes, with this patch routes with the same destination and metric automatically >> become multipath. From my testing, for link-locals this shouldn't make a difference >> as the interface must always be specified with % anyway. >> >> For non-LL addresses, this could indeed cause a regression in obscure setups. In my Having an address in the same prefix on two interfaces is not an "obscure setups". >> opinion though, I feel that it is very unlikely anyone who has two routes with the >> same prefix and metric (which AFAIK, isn't really a supported configuration without >> ECMP anyway) relies on this quirk. The most plausible setup relying on this I can >> think of would be a server with two interfaces on the same L2 segment, and a >> firewall somewhere that only allows the source address of one interface through. >> >> IMO, setups like that are more of a misconfiguration than a "practical use case" >> that'd make this a real regression, but I'd completely understand if it'd be enough >> to block this. > > There is really no reason to take a risk of a regression. If someone > wants ecmp with device only nexthops, then use the new nexthop infra to > do it. +1