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To: John Baldwin <jhb@FreeBSD.ORG>
Cc: Chris Costello <chris@calldei.com>, obrien@FreeBSD.ORG,
	Will Andrews <andrews@technologist.com>, freebsd-current@FreeBSD.ORG,
	"Jordan K. Hubbard" <jkh@zippy.osd.bsdi.com>
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From: "Louis A. Mamakos" <louie@TransSys.COM>
Subject: Re: /sys hierarchy 
References: <200007021744.KAA34752@john.baldwin.cx> 
In-reply-to: Your message of "Sun, 02 Jul 2000 10:44:23 PDT."
             <200007021744.KAA34752@john.baldwin.cx> 
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> 
> On 02-Jul-00 Chris Costello wrote:
> > On Sunday, July 02, 2000, John Baldwin wrote:
> >>    ip/                  - IPv4, IPv6, and IPsec bits from sys/netinet{,6}
> >>    tcp/                 - TCP                    "    "    "      "
> >>    udp/                 - UDP                    "    "    "      "
> > 
> >    Can this really be separated to such a degree?  Since TCP and
> > UDP are inet protocols, do they _need_ to be separated this way?
> 
> A directory listing of sys/netinet shows many in_* files, ip_* files,
> tcp_* files, and udp_* files.  Note that TCP and UDP aren't explicity
> tied to IP, they are simply wrapped inside of an IP packet.  In theory
> you can run TCP over IPX for example by using the same method of
> encapsulation.  Of course, someone more familiar with the actual code
> in the tree might provide some better insight on the feasibility of
> splitting these up.

Well, in theory maybe, but note that the TCP checksum is computed
over a the TCP header and a pseudo header composed of the IPv4 transport
addresses.  The layering of the protocols is a fine intellectual
notion, but don't confuse the layering with an efficient implementation.

louie


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