Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 beta 3/9/83; site celerity.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!hao!hplabs!sdcrdcf!sdcsvax!sdcc6!celerity!ron From: ron@celerity.UUCP (Ron McDaniels) Newsgroups: net.lan Subject: Re: (DoD) InterNet Header Checksum Message-ID: <222@celerity.UUCP> Date: Thu, 11-Oct-84 11:28:36 EDT Article-I.D.: celerity.222 Posted: Thu Oct 11 11:28:36 1984 Date-Received: Sat, 13-Oct-84 03:39:17 EDT References: <624@ttds.UUCP> <4985@brl-tgr.ARPA> <1723@sun.uucp> <> Reply-To: ron@celerity.UUCP ( McDaniels) Organization: Celerity Computing, San Diego Ca. Lines: 31 Summary: (.) There are good reasons not to perform header checksums in TCP/IP other that not being clever enough to do one's complement arithmetic. If you are running your network strictly on Ether the time to calculate them is wasted because the Ether CRC does a much more rigorous job of error detection than does a one's complement checksum. If you are talking to a "long haul" network via bog knows what kind of telephone lines, then the additional error check is useful ( read "mandatory"). I think that this issue of multiple layers of error checking is the chief complaint against the use TCP/IP for LANs. As an aside, in my favorite flavor of u**x (BSD 4.2) the integer variables "ipcksum", "tcpcksum" and "udpcksum" control the optional verification of checksums in the respective protocol layers. Both TCP and IP (in this specific implementation) always generate checksums. UDP does so only if the appropriate flag word is set. Also, UDP's verification of checksums is dependent upon BOTH the appropriate flag being set AND a received checksum equal zero. Considering how slowly the network code works (should have it's own dedicated cpu!) , I think that it is a reasonable optimization to eliminate protocol checksums when the link layer provides adequate error detection and you are only talking among like-minded nodes on your LAN. R. L. (Ron) McDaniels CELERITY COMPUTING 9692 Via Excelencia San Diego, California 92126 (619) 271-9940 {decvax || ucbvax || ihnp4 || akgua || philabs}!sdcsvax!celerity!ron