Subject: Re: The TCP and UDP checksum algorithm may soon need updating

From: Craig Partridge <[email-masked]>
Date: Thu, 11 Jun 2020 12:26:12 -0600

Two comments on the several notes that have gone past.

Michael Thomas raises a point about bugs.  He's quite right and there's
reason to believe that if we tracked the Internet paths on which checksum
errors took place, and compared the paths to find commonalities, we'd
locate broken/buggy equipment.  Jonathan Stone did some of that 20 years
ago and found a software bug in a vendor TCP (which the vendor updated in a
matter of days -- kudos to them) and a network interface vendor who was
shipping cards with defective hardware (and adamantly claimed our
measurements identifying their cards were wrong).

There was also a note (which I can't seem to find) to the effect of "the
errors in the papers don't match what I'm seeing on my systems."  That's
not a surprise.  Errors cluster around particular links or devices.
There's also some reason to believe error rates are higher on the fast
links.  So, depending on your environment and where your traffic goes, your
error rates may vary widely.  All the more reason to measure.

Thanks!

Craig
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From: Michael Thomas <[email-masked]>
Date: Thu, 11 Jun 2020 11:32:28 -0700

On 6/11/20 11:26 AM, Craig Partridge wrote:
> Michael Thomas raises a point about bugs.  He's quite right and 
> there's reason to believe that if we tracked the Internet paths on 
> which checksum errors took place, and compared the paths to find 
> commonalities, we'd locate broken/buggy equipment.  Jonathan Stone did 
> some of that 20 years ago and found a software bug in a vendor TCP 
> (which the vendor updated in a matter of days -- kudos to them) and a 
> network interface vendor who was shipping cards with defective 
> hardware (and adamantly claimed our measurements identifying their 
> cards were wrong).

Ha! I once got sent on site to find a tcp bug for my stack which we 
couldn't reproduce. Found it in about an hour or two. Got to see the 747 
that transported the space shuttle. Now *that's* a transport layer you 
don't want to find bugs in :)

>
> There was also a note (which I can't seem to find) to the effect of 
> "the errors in the papers don't match what I'm seeing on my systems."  
> That's not a surprise.  Errors cluster around particular links or 
> devices.  There's also some reason to believe error rates are higher 
> on the fast links.  So, depending on your environment and where your 
> traffic goes, your error rates may vary widely.  All the more reason 
> to measure.
>
It also wouldn't be surprising that it highly correlates with version 
1.0 vs 1.1. One of the depressing things about mobile phone stuff is the 
degree that vendors stop supporting updates, with it being particularly 
bad for Android.

Mike