Re: TCPv4 bad checksums

Shaw Carruthers (shaw@shawc.demon.co.uk)
Sun, 3 Jan 1999 17:01:29 +0000 (GMT)


On Sun, 3 Jan 1999, Jamie Lokier wrote:

>
> I have seen TCP checksum errors from Demon with `novj', so that's not a
> solution. They are rarer, though.
>
> I've done the sums by hand, and seen that the raw PPP data (as dumped by
> the kernel when PPP debugging is turned on) really does contain invalid
> TCP checksums. The IP header checksums are fine.
>
> The erroneous packets I looked at in detail appear to be misrouted to my
> machine, too. (I shouldn't be receiving them).
>

Misconfigured or malfunctioning border router at Demon is supposed to be
the prime suspect for non-vj checksum errors to us.

Turning off vj or restricting the window size gets rid of errors caused by
Ascend dropping packets. I reported remaining errors to Tim Preston at
Demon and he diagnosed a defective border router card.

-- 
Shaw Carruthers - shaw@shawc.demon.co.uk
London SW14 7JW UK
This is not a sig( with homage to Magritte).
  

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