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 0663A18C33A for ; Thu, 8 Aug 2024 12:24:36 +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=1723119877; cv=none; b=glTsHQjmEsN4YB/5h/zTSGyRVjcZUpQhTcZ7fbL0w4/Ig3jtIK4ejwW9dKFP8bv+C3HpjdJXNwryLezfl48SYR6+qCtggB8UyFNCLj053muUmbJakfRF/C/oVUM9rv1JBp+HxFclX5X4laM/6wrQmonPADaSNew7TQhLpoqjztY= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723119877; c=relaxed/simple; bh=xmu+iOqr/GKosgcrVkIiCMZHVd1rT2OA8gpI5CdgpbY=; h=From:To:Cc:Subject:In-Reply-To:References:Date:Message-ID: MIME-Version:Content-Type; b=JHxXpkfb6VsZdoPBVnhJtuct4+qxioCLEKqImvpGryQ0NZfm66Z7nbaNNFS5dthM95tstxW7rOQW/CbveE8WcZffO9DHSN0sPAidaKzGT0AhRDqxDdULu6eYQCeTLF0MjFuoCcyY8BJ2z2J/ulBaxC3sdDGQJqkSOLFgpX+UjVo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=IiTdOZLA; 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="IiTdOZLA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4B220C32782; Thu, 8 Aug 2024 12:24:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1723119876; bh=xmu+iOqr/GKosgcrVkIiCMZHVd1rT2OA8gpI5CdgpbY=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=IiTdOZLAWDHM8JsSg07sX5MhC3v9b16j9iDqcUGPtuaClyup/udzlpOdNh1at5Q3w 9n4M3KBpK9d5jftMad38wvX1WacezQhYFW4Gk+893s8HHi6+75P7IisA1UmOKLRx4D gO8Y5ZIRfb697UjfE4HiVJuUWS2QDdWLdhSJ6jqpA4kx0L1Vn36E7Q2G45Pgb0TXiu bF1jKmmDbkwMqa6GIcJDvVIHS+QOXYaaKUO4bE+rGLg6015mQ3A5Rbb1OYgo0fyZ0a ItyUgOowTVMZIcR/Qz4V0s26jt1VLouXiX5ti9dChUULGqLksRk4Zx80a8DdQO8sb3 xmijAs491ciGA== Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id 9D43014AD6C4; Thu, 08 Aug 2024 14:24:33 +0200 (CEST) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: djduanjiong@gmail.com Cc: netdev@vger.kernel.org Subject: Re: [PATCH v3] veth: Drop MTU check when forwarding packets In-Reply-To: <00f872ac-4f59-4857-9c50-2d87ed860d4f@Spark> References: <20240808070428.13643-1-djduanjiong@gmail.com> <87v80bpdv9.fsf@toke.dk> <87mslnpb5r.fsf@toke.dk> <00f872ac-4f59-4857-9c50-2d87ed860d4f@Spark> X-Clacks-Overhead: GNU Terry Pratchett Date: Thu, 08 Aug 2024 14:24:33 +0200 Message-ID: <87h6bvp5ha.fsf@toke.dk> 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: quoted-printable djduanjiong@gmail.com writes: > This is similar to a virtual machine that receives packets larger than > its own mtu, regardless of the mtu configured in the guest.=C2=A0=C2=A0Or= , to > put it another way, what are the negative effects of this change? Well, it's changing long-standing behaviour (the MTU check has been there throughout the history of veth). Changing it will mean that applications that set the MTU and rely on the fact that they will never receive packets higher than the MTU, will potentially break in interesting ways. You still haven't answered what's keeping you from setting the MTU correctly on the veth devices you're using? -Toke