On Wed, Oct 23, 2002 at 03:00:12PM -0700, Jason R Thorpe wrote:
> On Wed, Oct 23, 2002 at 11:25:44PM +0200, Manuel Bouyer wrote:
> 
>  > After seeing Nicolas Saurbier's mail on netbsd-help
>  > http://mail-index.netbsd.org/netbsd-help/2002/10/21/0003.html
>  > about the TCP packet sizes and the default's route MTU, I tried a
>  > route change default xxxx -mtu 1500 on the 1.6 source host. I get the
>  > full speed again.
>  > Changing the MTU on the target host doesn't change anything.
>  > 
>  > I guess the default MTU for a route entry should be the one of the interface
>  > it goes though, isn't it ? It looks like something is broken here ...
> 
> Something is surely fishy, but the route entry should NOT have the mtu
> for its interface.  Doing so has caused a number of problems with path
> MTU discovery in the past, and I'm not particularly interested in having
> to fix it again.
> 
> Is Path MTU discovery enabled on your machine?

No (because is has caused me more troubles than it's worth):
antioche:/home/bouyer>sysctl -a |grep mtu
net.inet.ip.mtudisc = 0

I've also noticed the problem on a machine with a 10Mbs ethernet:
750KB/s with FTP, instead of the expected 1MB/s
In each test case the default route was used (I can't easily test on local
network).

--
Manuel Bouyer, LIP6, Universite Paris VI.           Manuel.Bouyer@lip6.fr
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