Date: Wed, 6 Jun 2001 22:49:18 -0700 From: Bill Fenner <fenner@research.att.com> To: louie@transsys.com Cc: freebsd-hackers@freebsd.org Subject: Re: How to disable software TCP checksumming? Message-ID: <200106070549.WAA06248@windsor.research.att.com> References: <20010529144114.I19771@luke.immure.com> <20010529221107.C49875@skriver.dk> <20010529155212.M19771@luke.immure.com> <20010530045200.A1031@hades.hell.gr> <20010529235215.A60177@luke.immure.com> <20010530085155.B24096@Odin.AC.HMC.Edu> <200105310204.f4V248n15260@whizzo.transsys.com>
next in thread | previous in thread | raw e-mail | index | archive | help
>The TCP checksum protects more than just the contents of the packet >on the wire; it's also a (somewhat) weak check on the contents >of your packet sitting in memory, and as it's going over the bus >in your computer between memory and peripherals and for other end-to-end >sorts of issues. In fact, Jonathan Stone at Stanford did some measurements of checksum errors for his thesis, and found that on a given link in the Stanford residences there were a surprising (small, but measurable) number of packets with IP header checksum errors with what appeared to be DMA errors -- e.g. 4 bytes missing from the middle of the header. When the end to end checksum is really memory to memory, it can catch errors like this... Bill To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200106070549.WAA06248>