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SubjectRe: Linux TCP impotency
On Sun, May 13, 2001 at 10:54:15PM +0200, ahu@ds9a.nl wrote:
> On Sun, May 13, 2001 at 09:38:53PM +0200, clock@ghost.btnet.cz wrote:
> > Using 2.2.19 I discovered that running two simultaneous scp's (uses up whole
> > capacity in TCP traffic) on a 115200bps full duplex serial port nullmodem cable
> > causes the earlier started one to survive and the later to starve. Running bcp
> > instead of the second (which uses UDP) at 11000 bytes per second caused the
> > utilization in both directions to go up nearly to 100%.
> >
> > Is this a normal TCP stack behaviour?
>
> Might very well be. Read about different forms of (class based) queuing
> which try (and succeed) to improve IP in this respect. TCP is not fair and
> IP has no intrinsic features to help you. http://ds9a.nl/2.4Routing contains
> some explanations and links.
>
> SFQ sounds like it might fit your bill.
>
> Regards,
>
> bert
>
> --
> http://www.PowerDNS.com Versatile DNS Services
> Trilab The Technology People
> 'SYN! .. SYN|ACK! .. ACK!' - the mating call of the internet
> -

I was about to report the same 'od' behaviour : I have 3
machines, connected via a HUB at 100 Mb/s half duplex.

From machine A : rsh B dd if=/dev/zero bs=8192 | dd of=/dev/null

=> transfert around 10/11 MB/s (B => A)

Now, I start a second transfert from machine C :

rsh B dd if=/dev/zero bs=8192 | dd of=/dev/null

=> transfert around 10/11 MB/s between B and C, almost nothing
between A and B (ie, the connexion is stalled between A and B).

If I stop the second transfert, I takes many seconds for
the transfert to restart between A and B.

On a highly saturated network, I have already seen such a
behavior.

Is that related to the IP adresses, the lowest being served
first ?

A+,
--
Thierry Danis
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