From owner-freebsd-questions@FreeBSD.ORG Thu May 24 19:26:10 2007 Return-Path: X-Original-To: freebsd-questions@freebsd.org Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id 6DBE916A468 for ; Thu, 24 May 2007 19:26:10 +0000 (UTC) (envelope-from cswiger@mac.com) Received: from mail-out3.apple.com (mail-out3.apple.com [17.254.13.22]) by mx1.freebsd.org (Postfix) with ESMTP id 5579213C480 for ; Thu, 24 May 2007 19:26:10 +0000 (UTC) (envelope-from cswiger@mac.com) Received: from relay7.apple.com (relay7.apple.com [17.128.113.37]) by mail-out3.apple.com (Postfix) with ESMTP id 6143A204302; Thu, 24 May 2007 12:25:35 -0700 (PDT) Received: from relay7.apple.com (unknown [127.0.0.1]) by relay7.apple.com (Symantec Mail Security) with ESMTP id 3CBEC304C7; Thu, 24 May 2007 12:26:10 -0700 (PDT) X-AuditID: 11807125-a2274bb00000318d-4e-4655e6d29863 Received: from [17.214.13.96] (cswiger1.apple.com [17.214.13.96]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (No client certificate requested) by relay7.apple.com (Apple SCV relay) with ESMTP id 28A7330044; Thu, 24 May 2007 12:26:10 -0700 (PDT) In-Reply-To: <340a29540705241210qa6895bem9d4aa1a5d2dd05a0@mail.gmail.com> References: <340a29540705241210qa6895bem9d4aa1a5d2dd05a0@mail.gmail.com> Mime-Version: 1.0 (Apple Message framework v752.2) Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed Message-Id: <1EE2ED95-376C-461F-A65D-5191FBA238C9@mac.com> Content-Transfer-Encoding: 7bit From: Chuck Swiger Date: Thu, 24 May 2007 12:26:09 -0700 To: Andrew Falanga X-Mailer: Apple Mail (2.752.2) X-Brightmail-Tracker: AAAAAA== Cc: freebsd-questions Subject: Re: How does FreeBSD handle tcp checksum offloading X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 24 May 2007 19:26:10 -0000 On May 24, 2007, at 12:10 PM, Andrew Falanga wrote: > I'm curious as to how FreeBSD handles checksum offloading for TCP > packets. Is this on by default? If a particular NIC supports checksum offloading, it is typically enabled by default. > It seems that it's only relevant for specific drivers rather than > something that's just assumed. That's correct. Most of the gigabit NICs support it, but few of the older NICs do. > How can I determine if this is supported for the hardware I'm > running? Is it > common for tcp checksum offloading to be in the fxp driver? Can one > turn it off (though, it honestly sounds like no one would wish to do > so)? You can use ifconfig to see whether the RXCSUM & TXCSUM options are listed, and you can use ifconfig to enable or disable it: rxcsum, txcsum If the driver supports user-configurable checksum offloading, enable receive (or transmit) checksum offloading on the inter- face. Some drivers may not be able to enable these flags inde- pendently of each other, so setting one may also set the other. The driver will offload as much checksum work as it can reliably support, the exact level of offloading varies between drivers. -rxcsum, -txcsum If the driver supports user-configurable checksum offloading, disable receive (or transmit) checksum offloading on the inter- face. These settings may not always be independent of each other. I don't believe that the fxp NICs support checksum offloading. -- -Chuck