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Re: Linux Kernel Summit

From: Tripp Lilley <tlilley_at_perspex.com>
Date: 2001-04-02 23:36:47 CEST

On Mon, 2 Apr 2001, Greg Stein wrote:

> I tend to agree here. But if it is cheap, using HTTP systems, then it
> shouldn't be a problem for us [to satisfy the overly paranoid]. It isn't
> going to help with TCP (which is already checksum'd), but will help with
> problems in an end-to-end connection (i.e. a proxy that mucks it up). As you
> point out, though, I'm not aware of any observances of this, nor of any
> broken TCP stacks that don't checksum and verify the result.
> [ hmm. actually, after I wrote that, I seem to recall there *was* a stack
> somewhere that didn't check the checksums... ]

Actually, at Interop we discovered a surprising number of "in the middle"
devices (proxies, caches, firewalls, traffic shapers) that ignored the TCP
checksum, or recomputed it incorrectly, or silently changed data -and-
recomputed the checksum (so the receiving end wasn't aware that anything
was wrong).

"surprising" in this context is evaluated as "more than zero", but I
neither remember exact numbers, nor remember nor would be allowed to say
which vendors or products.

But it happens. So it's best to guard against it. Which sucks.

   Joy-Loving * Tripp Lilley  *  http://stargate.eheart.sg505.net/~tlilley/
  "Fiber makes you poop." -- From <http://www.pvponline.com/bts_studio.php3>
Received on Sat Oct 21 14:36:27 2006

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