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[34.145.139.141]) by smtp.gmail.com with UTF8SMTPSA id 00721157ae682-78fb4377f5csm43645607b3.2.2025.12.22.06.05.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 22 Dec 2025 06:05:29 -0800 (PST) Date: Mon, 22 Dec 2025 09:05:28 -0500 From: Willem de Bruijn To: Vadim Fedorenko , "David S. Miller" , David Ahern , Eric Dumazet , Paolo Abeni , Simon Horman , Willem de Bruijn , Jakub Kicinski Cc: Shuah Khan , Ido Schimmel , netdev@vger.kernel.org, Vadim Fedorenko Message-ID: In-Reply-To: <20251221192639.3911901-1-vadim.fedorenko@linux.dev> References: <20251221192639.3911901-1-vadim.fedorenko@linux.dev> Subject: Re: [PATCH net v3 1/2] net: fib: restore ECMP balance from loopback Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Vadim Fedorenko wrote: > Preference of nexthop with source address broke ECMP for packets with > source addresses which are not in the broadcast domain, but rather added > to loopback/dummy interfaces. Original behaviour was to balance over > nexthops while now it uses the latest nexthop from the group. To fix the > issue introduce next hop scoring system where next hops with source > address equal to requested will always have higher priority. > > For the case with 198.51.100.1/32 assigned to dummy0 and routed using > 192.0.2.0/24 and 203.0.113.0/24 networks: > > 2: dummy0: mtu 1500 qdisc noqueue state UNKNOWN group default qlen 1000 > link/ether d6:54:8a:ff:78:f5 brd ff:ff:ff:ff:ff:ff > inet 198.51.100.1/32 scope global dummy0 > valid_lft forever preferred_lft forever > 7: veth1@if6: mtu 1500 qdisc noqueue state UP group default qlen 1000 > link/ether 06:ed:98:87:6d:8a brd ff:ff:ff:ff:ff:ff link-netnsid 0 > inet 192.0.2.2/24 scope global veth1 > valid_lft forever preferred_lft forever > inet6 fe80::4ed:98ff:fe87:6d8a/64 scope link proto kernel_ll > valid_lft forever preferred_lft forever > 9: veth3@if8: mtu 1500 qdisc noqueue state UP group default qlen 1000 > link/ether ae:75:23:38:a0:d2 brd ff:ff:ff:ff:ff:ff link-netnsid 0 > inet 203.0.113.2/24 scope global veth3 > valid_lft forever preferred_lft forever > inet6 fe80::ac75:23ff:fe38:a0d2/64 scope link proto kernel_ll > valid_lft forever preferred_lft forever > > ~ ip ro list: > default > nexthop via 192.0.2.1 dev veth1 weight 1 > nexthop via 203.0.113.1 dev veth3 weight 1 > 192.0.2.0/24 dev veth1 proto kernel scope link src 192.0.2.2 > 203.0.113.0/24 dev veth3 proto kernel scope link src 203.0.113.2 > > before: > for i in {1..255} ; do ip ro get 10.0.0.$i; done | grep veth | awk ' {print $(NF-2)}' | sort | uniq -c: > 255 veth3 > > after: > for i in {1..255} ; do ip ro get 10.0.0.$i; done | grep veth | awk ' {print $(NF-2)}' | sort | uniq -c: > 122 veth1 > 133 veth3 > > Fixes: 32607a332cfe ("ipv4: prefer multipath nexthop that matches source address") > Signed-off-by: Vadim Fedorenko Reviewed-by: Willem de Bruijn