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[2a10:fc81:a806:d6a9::1]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-38f259d58f3sm20967778f8f.73.2025.02.20.08.27.37 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 20 Feb 2025 08:27:37 -0800 (PST) Date: Thu, 20 Feb 2025 17:27:35 +0100 From: Stefano Brivio To: Jon Maloy Subject: Re: [PATCH v2] tap: always set the no_frag flag in IPv4 headers Message-ID: <20250220172735.757f05a7@elisabeth> In-Reply-To: <20250219152041.2257268-1-jmaloy@redhat.com> References: <20250219152041.2257268-1-jmaloy@redhat.com> Organization: Red Hat X-Mailer: Claws Mail 4.2.0 (GTK 3.24.41; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-MFC-PROC-ID: 4JovoJ1Bfai-I3F09MDPmUYPyE0L1YheiJ1gOuvq6Yg_1740068860 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-ID-Hash: N3QKWD3YAOIIJHN37T6FOONZAHWRNMCN X-Message-ID-Hash: N3QKWD3YAOIIJHN37T6FOONZAHWRNMCN X-MailFrom: sbrivio@redhat.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: passt-dev@passt.top, lvivier@redhat.com, dgibson@redhat.com X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: On Wed, 19 Feb 2025 10:20:41 -0500 Jon Maloy wrote: > When studying the Linux source code and Wireshark dumps it seems like > the no_frag flag in the IPv4 header is always set. Following discussions > in the Internet on this subject indicates that modern routers never > fragment packets, and that it isn't even supported in many cases. > > Adding to this that incoming messages forwarded on the tap interface > never even pass through a router it seems safe to always set this flag. > > This makes the IPv4 headers of forwarded messages identical to those > sent by the external sockets, something we must consider desirable. > > Signed-off-by: Jon Maloy > --- > v2: Updated checksum algorithm to consider the change Applied. -- Stefano