Date: 08 Jun 2001 14:42:46 +0200 From: Assar Westerlund <assar@FreeBSD.ORG> To: Ruslan Ermilov <ru@FreeBSD.ORG> Cc: tlambert2@mindspring.com, freebsd-hackers@FreeBSD.ORG Subject: Re: How to disable software TCP checksumming? Message-ID: <5lofrzrvll.fsf@assaris.sics.se> In-Reply-To: Ruslan Ermilov's message of "Fri, 8 Jun 2001 15:35:44 %2B0300" 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> <200106070549.WAA06248@windsor.research.att.com> <3B208F11.87722148@mindspring.com> <5lk82ntb0o.fsf@assaris.sics.se> <20010608153544.C87737@sunbay.com>
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Ruslan Ermilov <ru@FreeBSD.ORG> writes:
> On Fri, Jun 08, 2001 at 02:24:23PM +0200, Assar Westerlund wrote:
> > Terry Lambert <tlambert2@mindspring.com> writes:
> > > This all came from IP headers being 14 bytes long, instead
> > > of 16.
> >
> > Hu? An IPv4 header (not including options) is 20 bytes long.
> >
> Terry meant the length of an IPv4 header up to but not including
> the checksum field.
I'm confused. From rfc791:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| IHL |Type of Service| Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |Flags| Fragment Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live | Protocol | Header Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Which to me says that an IP header up to but not including the
checksum is 10 bytes?
/assar
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