Date: Tue, 15 Jun 2004 23:39:27 -0500 From: Kevin Day <toasty@dragondata.com> To: yongari@kt-is.co.kr Cc: freebsd-sparc64@freebsd.org Subject: Re: TCP/UDP cksum offload on hme(4) Message-ID: <264D82AE-BF4F-11D8-A89B-000A95A8A1F2@dragondata.com> In-Reply-To: <20040616034520.GB7887@kt-is.co.kr> References: <20040616034520.GB7887@kt-is.co.kr>
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On Jun 15, 2004, at 10:45 PM, Pyun YongHyeon wrote: > > 1. UDP TX cksum offload has an issue. The hardware doesn't flip the > cksum bits when the computed cksum is 0x0000. I have no idea this > is the reason why STP2002QFP says it supports only TCP RX/TX cksum. > (pp. 29, pp. 40, pp. 42) > > I'm not sure if you're aware of this or not, but: > If the computed checksum is zero, it is transmitted as all ones > (the > equivalent in one's complement arithmetic). An all zero > transmitted > checksum value means that the transmitter generated no checksum > (for > debugging or for higher level protocols that don't care) So, if a UDP packet has an all zero checksum, it's supposed to mean there was no checksum performed. If you legitimately came up with 0x0000 for a checksum, you're supposed to set the header field to 0xffff.
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