vge traffic problem

[Pyun YongHyeon]

On Mon, Jan 11, 2010 at 06:49:00PM -0800, Pyun YongHyeon wrote:
> On Mon, Jan 11, 2010 at 05:22:49PM -0800, David Ehrmann wrote:

[...]

> > I did this one between two similar FreeBSD systems (8.0 and 8.0 RC1, I 
> > think).  There wasn't an error in netstat -s on the receiver, but I ran 
> > tcpdump, anyway.  The checksums were good, but iperf ended with "read 
> > failed: connection refused."  On the non-vge box, once the vge box is 
> > done sending, it sends four identical UDP packets to the vge host, I 
> > think to ask it for sending statistics.  Instead of statistics, it got 
> > back an ICMP packet saying "port unreachable."  This happens with a 
> > freebsd client, but not a linux client (I didn't confirm the ICMP 
> > message with tcpdump, though).  All iperf versions are the same (2.0.4), 
> > but the linux one doesn't have any threading (which shouldn't be an 
> > issue when I'm not using that option).
> 
> It seems iperf on FreeBSD was broken. It incorrectly generates
> huge-packet with IP length 0 so other host disconnected the
> TCP connection. Not sure it could be related with threading though.
> Use netperf instead, it would be more reliable than iperf.
> 

Disabling threading make iperf work again. And don't be surprised
at the dropped counter of iperf, it's normal for UDP frames. Good
hardware and fast system may have better numbers but you can't
completely remove dropped counters.