Linux-kernel mailing list archive 1998-42,: Re: Massive TCPv4 bad checksum

# Re: Massive TCPv4 bad checksum

Andi Kleen (ak@muc.de)
Mon, 19 Oct 1998 00:19:37 +0200

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On Sun, Oct 18, 1998 at 08:18:17PM +0200, H.J. Lu wrote:
> > >>
> >
> > > I can tell my SLIP speed is slower than 2.0 and there are quite
> > > some corrupted packets come over SLIP link.
> >
> > Some broken modem server have buggy VJ compression functions that can't
> > cope with the new RFC1323/SACK TCP options Linux 2.1 sends. Try turning
> > them off with
> >
> > echo 0 >/proc/sys/net/ipv4/tcp_sack
> > echo 0 >/proc/sys/net/ipv4/tcp_timestamps
> > echo 0 >/proc/sys/net/ipv4/tcp_window_scaling
> >
> > Will only take effect for new TCP connections afterward.
> >
>
> I tried that. I still got back TCP checksum. But the speed
> seems faster than before. BTW, the other side of my SLIP
> link is runnings Linux 2.1.102 with Cyclades card and some
> modems. Should they also turn off the new RFC1323/SACK TCP
> options?

No the options are negotiated and only used when both sides like them.
Also the options don't need to be set on the router, but on the end hosts.
If you're running linux as the terminal server it must be something else -
afaik there are no known bugs in linux vj compression regarding tcp options
(I think there was an issue with masquerading & tcp options, but I assume
you don't use that?)

-Andi

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