[ECOS] rattler PB

Nick Garnett nickg@ecoscentric.com
Thu Dec 18 10:41:00 GMT 2003

"Slawek" <sgp@telsatgp.com.pl> writes:

> Andrew Lunn wrote:
> > On Thu, Dec 18, 2003 at 09:22:47AM +0100, alix t wrote:
> > > We try to develop applications with goahead web server
> > > and other network services on rattler card , but our
> > > applications often crash.
> > > So we want first validate ethernet and IP stacks.
> > > I think to send very large packets is a good test to
> > > validate ethernet stack.
> > 
> > Its not a realistic test. I doubt any application will use such large
> > IP packets. UDP has a maximum packet size of around 4Kbytes. TCP will
> > generally use either around 800 bytes or around 1500 bytes depending
> > on if MTU discovery is being used. 
> > 
> > Only a custom application which is not using UDP or TCP can generate
> > such big IP packets. Typically this would be for connecting super
> > computers together using HIPI interfaces. Thats why IPv6 has a jumbo
> > packet which can be bigger than 64Kbytes. 
> > 
> > I suggest you try more realistic tests.
> Keep in mind that he has tried to send big packets *to* the device,
> *not* write a special program for the device which failed when
> sending those.
> If such packets causes the device to crash, then the *final* product
> could be *crashed* as well, by accident or intentionally.

I usually test any ethernet interface I am working on by flood
pinging it with large packets. The TCP/IP stack is quite robust enough
to handle this. Of course there may be issues in the device driver,
and this sometimes causes the stack to run out of mbufs. It is very
unlikely that doing this would actually cause a crash.

Nick Garnett                    eCos Kernel Architect
http://www.ecoscentric.com      The eCos and RedBoot experts

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