From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CB36B315D3A for ; Thu, 18 Sep 2025 16:29:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758212988; cv=none; b=G2ZqgvcFU97rUyFT/t32eE7Vm3lgvwu0V0XHmQlJxKCMbdZFH9xTmQm7ZbVbMGvF0iPukkgxjMWQsgCbvh9kxw/Luu6pvblX5MsGQ6Di6BjZSGShZIYmdFRqk17cY0DQOgyBIF9in2/0ypQLvUaCfsxX3dBJipE5eznMdu58mQ8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758212988; c=relaxed/simple; bh=io3Bg9ao1VouLRigE0Z46PgAqHjx7x6JaOOZPHjuHJ8=; h=Message-ID:Date:MIME-Version:Subject:To:References:From: In-Reply-To:Content-Type; b=UrqW/hhXt/yYE3Spw5xkPkFY8HuJl67oMMj9o1uQJMe9idBBgKsGGQ1FaiKutfW08xybGMGtu2sZaz6jXreb6yQ2OHE4ka2d+lrUWAfre8/3ZYzN40myHWyNxEHp0Kxyz2qOfE5iKBGGG1CrUtewKY6K462iO0Ag59iHVGza36Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ABZVBysM; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="ABZVBysM" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 133C1C4CEE7 for ; Thu, 18 Sep 2025 16:29:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1758212988; bh=io3Bg9ao1VouLRigE0Z46PgAqHjx7x6JaOOZPHjuHJ8=; h=Date:Subject:To:References:From:In-Reply-To:From; b=ABZVBysMG04pEfYOf5/Up12AeByAir7bcI5qIvIGMm3DqZOqepU6pSDwC40N7yb7z VEp7sCUymaXd0fZ9T94gDlFz7XFRtJnXF92MILRYYbyTty5oWiFl8su0tkvUZNfIZL 7se+6iWfKUJatUO1jBtDoL6DwLxSqZPRw+d7x8oaUQns3rc9VVa8g1FuX9KHOyCPQW NMhl/trm0qu3tWfLx/T8qK1N5K0nfIetM5CAyjwHWZD/HmGMz2RNrYP4XNCAqIKRZA Blk3eaX+iCULgz/pAkiEFEg51ZtTqOUzcWIeKAHqWlLUSqsYL1Zr2oR4ZTW1LxRMyq 10sXri8itIj5Q== Message-ID: <7ecc8d89-6454-4b83-bef5-3b7d66fe2655@kernel.org> Date: Thu, 18 Sep 2025 18:29:45 +0200 Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Beta Subject: Re: [PATCH mptcp-net v2 1/2] mptcp: pm: in-kernel: usable client side with C-flag To: MPTCP Linux References: <20250916-pm-c-flag-client-default-v2-0-3be2c5bc4d6a@kernel.org> <20250916-pm-c-flag-client-default-v2-1-3be2c5bc4d6a@kernel.org> From: Matthieu Baerts Content-Language: en-GB, fr-BE Autocrypt: addr=matttbe@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Hello, On 16/09/2025 13:01, Matthieu Baerts (NGI0) wrote: > When servers set the C-flag in their MP_CAPABLE to tell clients not to > create subflows to the initial address and port, clients will likely not > use their other endpoints. That's because the in-kernel path-manager > uses the 'subflow' endpoints to create subflows only to the initial > address and port. > > If the limits have not been modified to accept ADD_ADDR, the client > doesn't try to establish new subflows. If the limits accept ADD_ADDR, > the routing routes will be used to select the source IP. > > The C-flag is typically set when the server is operating behind a legacy > Layer 4 load balancer, or using anycast IP address. Clients having their > different 'subflow' endpoints setup, don't end up creating multiple > subflows as expected, and causing some deployment issues. > > A special case is then added here: when servers set the C-flag in the > MPC and directly sends an ADD_ADDR, this single ADD_ADDR is accepted. > The 'subflows' endpoints will then be used with this new remote IP and > port. This exception is only allowed when the ADD_ADDR is sent > immediately after the 3WHS, and makes the client switching to the 'fully > established' mode. After that, 'select_local_address()' will not be able > to find any subflows, because 'id_avail_bitmap' will be filled in > mptcp_pm_create_subflow_or_signal_addr(), when switching to 'fully > established' mode. > > Fixes: df377be38725 ("mptcp: add deny_join_id0 in mptcp_options_received") > Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/536 > Signed-off-by: Matthieu Baerts (NGI0) > --- > Notes: > - I tried to find a simple solution that can hopefully be backported to > cover the 'CDN' use-case. > - I tried to find a solution respecting the 'accepted add addr' limit, > but I don't see how to... That's why here I limit the exception a > maximum: when this limit is 0 (default case), only the first ADD_ADDR, > etc. Feel free to share what you think about that. > - I have some additional code doing some cleanup, and I started to look > at #503, which is a bit linked to that. > - v2: move conditions to new helper (Geliang) + rename var, squash comm. (...) > diff --git a/net/mptcp/pm_kernel.c b/net/mptcp/pm_kernel.c > index f30df8e884a0b3de9fb092e5774cafe08f6350ce..d7cd89fa6a11a1ea7703edbfbdf2bbe86a6a3054 100644 > --- a/net/mptcp/pm_kernel.c > +++ b/net/mptcp/pm_kernel.c (...) > @@ -409,6 +411,10 @@ static unsigned int fill_local_addresses_vec(struct mptcp_sock *msk, > locals[i].flags = entry->flags; > locals[i].ifindex = entry->ifindex; > > + if (c_flag_case) Small note: here, it should be: if (c_flag_case && (entry->flags & MPTCP_PM_ADDR_FLAG_SUBFLOW)) (but this doesn't change the global idea of this patch, I can apply it when applying the patch) > + __clear_bit(locals[i].addr.id, > + msk->pm.id_avail_bitmap); > + > /* Special case for ID0: set the correct ID */ > if (mptcp_addresses_equal(&locals[i].addr, &mpc_addr, locals[i].addr.port)) > locals[i].addr.id = 0; (...) Cheers, Matt -- Sponsored by the NGI0 Core fund.