Re: Van J compression?
Andi Kleen (ak@muc.de)
Sun, 27 Dec 1998 23:29:20 +0100
On Sun, Dec 27, 1998 at 11:11:50PM +0100, Riley Williams wrote:
> Hi Andi.
>
> >>> The search for TCPv4 bad checksums continues. adding novj to the
> >>> ppp options seems to have fixed the problem. Still doing more
> >>> testing to ensure that the router (the remote point of my point
> >>> to point) has a bad ppp implementation and not me. Since it has a
> >>> bad finger implementation, and ppp works fine over null modems
> >>> and telnet sessions, I dare say the problem is with the router.
>
> >> Probably a useful check is to find out if the "bad Van J
> >> compression" problem is bad in the same way each time. If so, then
> >> it could be an idea to include some sort of workaround for it in
> >> the PPP routines, similar to the way we've worked round the F00F
> >> bug rather than insist that users upgrade...
>
> > "We" didn't have a VJ compression problem. Some terminal servers
> > (e.g. Ascend?) seem to have buggy VJ compression functions in some
> > firmware releases that can't deal with the extended TCP options
> > used by Linux 2.1: TCP timestamp, TCP sack and TCP window scaling.
>
> > Workaround is to turn them off:
>
> > echo 0 > /proc/sys/net/ipv4/tcp_{window_scaling,timestamps,sack}
>
> Two questions:
>
> 1. Will the above command work as written, or should it be three
> separate commands?
In zsh it works as writen, in bash you need
for i in /proc/sys/net/ipv4/tcp_{window_scaling,timestamps,sack} ; do echo > $i 0 ; done
> 2. Can the PPP code auto-detect that it's dealing with just such a
> buggy chunk of firmware? If so, can it automagically turn those
> options off?
It can't.
-Andi
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