From mboxrd@z Thu Jan 1 00:00:00 1970 From: Antony Stone Subject: Re: Checksumming Issues Date: Fri, 21 Nov 2003 20:27:21 +0000 Sender: netfilter-admin@lists.netfilter.org Message-ID: <200311212027.hALKRQj29614@agate.rockstone.co.uk> References: Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: Errors-To: netfilter-admin@lists.netfilter.org List-Help: List-Post: List-Subscribe: , List-Id: List-Unsubscribe: , List-Archive: Content-Type: text/plain; charset="us-ascii" To: netfilter@lists.netfilter.org On Friday 21 November 2003 8:15 pm, Leonid Veytser wrote: > A general question about checksumming. If I change the destination address > in the IP header, then of course I need to recalculate the IP header > checksum. "You" the user (or system administrator) do not need to recalculate any checksums - the SNAT or DNAT code does this for you. > But do I have to recalculate the checksum of the next protocol > header (ie TCP, UDP, etc)? No. Everything is handled for you in the background. Anyway, if you only change the IP address (source and/or destination), the TCP or UDP checksum remains valid. Antony. -- Feeling bad at breakfast because you don't have a hangover is evidence of a complex emotional life it can take many years to perfect. - Pete McCarthy, The Road to McCarthy Please reply to the list; please don't CC me.