Reproduceable data dependent TCP checksum errors

About five years ago I had a data dependent problem with my SDSL link. There were a few bit patters that had some trouble, but the one that was guaranteed to fail was a string of capital 'U' characters. (The bit pattern for ASCII 'U' is 01010101.) I first noticed the problem when a string of U's occurred in a CD-ROM (.iso) image of a Red Hat Linux release. I was able to work around the problem by continuing the download via dial-up long enough to get past the problem, then re-establish the DSL connection. Within a year or so, I noticed the problem was gone, with no hardware/software changes on my end.

Just for grins, my next followup to this post will be a string of U's.

Scott

And NNTP?

Here's a string of U's, as promised:

UUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUU

Scott

Yes but you provide no complete path to the file, thus no one can try to reproduce the error.

Billy Y..

Here's one that fails:

Orin.

My mistake - the path was in what you posted earlier(!)

Well, using NetBSD v2.0 and lynx I got the file ok, no problem at all. It is currently sitting on that same system at -

Billy Y..

Thanks!

I got 4626360 bytes from

Now they want me to upgrade the firmware on the modem (it's aready at the latest version that I can find) or try a different brand...

Yes, the path and host was in the ethereal trace, but I should have posted it anyway...

Orin.

I can get a Zoom locally cheap enough - I don't really expect it to make a difference.

It was ironic that during my research, I couldn't download the Verizon setup pdf from the Zoom web site. Better go grab it here at work! Orin.

I'm using a Zyxel - it works well but it does get pretty warm, you can't leave one on top of some other heat producing device - the combination will get it too hot. They are also pretty cheap on ebay.

I also have a Netopia box - I would not recommend them not only because has their support web site always sucked, now it has also been dumbed down heavily and quite a bit of very useful info has been pulled. And replaced with crap. They define "NIC" as the "National Internet Commission" for example. Real confidence-inspiring stuff.

I can say neither of these has any crc-related problem with the very same file though...

Billy Y..

Here is one of my killer patterns. The ping is done from a different ISP:

ping -p 000000000000df7df3db00000000000000 -s 380

Over 90% of these get corrupted. Drop the size down to the default and around 20% get corrupted.

Orin.

Update.

I managed to get a ping from an external ISP to the gateway to fail. My ISP fixed this by re-routing the return path of these pings. Didn't help my DSL of course.

Finally, a week ago, they replaced some hardware and life is good. No more corruption.

Orin.