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SubjectRe: UDP network problem
On Sun, 17 Aug 1997 kwrohrer@enteract.com wrote:

> And lo, mshar@vax.ipm.ac.ir saith unto me:
> > Thanks for the recommendation to use TCP. Actually I want to use UDP in
> > a system called DIPC (Distributed Inter-Process Communication.) It already
> > has TCP support. The main attraction of UDP is its speed in sending smaller
> > and independent packets.
> >
> > My real problem, however, is that I could not send more than 3250 bytes
> > ever! Not a single time. It is hard to attribute such a consistent error
> > with transient reasons. I've had very little difficulty with 3250 and
> > less amounts of data (a 57600 bps point-to-point connection is not very
> > noisy, or very speedy for a 486 to handle).
> >
> > Could there be an inherent limitation in the kernel or other user-space
> > networking code?
> I've had no problems sending UDP packets as large as 8k (payload) over
> loopback and (ne2000) ethernet, on kernel 2.1.29. My only problem was
> that sometimes some data would never arrive at the receiver, even using
> TCP, even when no sends returned errors...I chalked it up to a bug in
> my code, though the losses did coincide with "socket destroy delayed"
> messages. I figure it's been fixed by now, but have been too wary of
> the new "kernels" to actually try one.
>
> Anyway, try running the "far end" on the same machine, and see if that
> changes anything...
>
> Keith
>
Isn't there a maximum allowed packet length of 1500 bytes on Ethenet??
Doesn't this confine the maximum data area to about 1480 bytes to leave
room or the header?? You can't fragment UDP so, as I understand it, you
should never be able to send more than 1480 bytes on UDP. Or am I missing
something?? Have the Specs changed? Can you now blast through anything??
If so, most Ethernet drivers won't handle it because the shared RAM is
usually cut up into buffers that assume 1500 bytes max (actually 2048 on
some that can only a set "pages").

If you can now blast through anything, something is broken. I sure would
not like to see 8k packet lenghts on my LAN. This would monopolize the
LAN and prevent complient packets from getting their fair share on the
wire.


Cheers,
DJ
Richard B. Johnson
Analogic Corporation
Penguin : Linux version 2.1.50 on an i586 machine (66.15 BogoMips).
Warning : It's hard to stay on the trailing edge of technology.
Linux : Engineering tool
Windows : Typewriter


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