From owner-freebsd-net  Sat May 18  1:54: 0 2002
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Date: Sat, 18 May 2002 01:53:09 -0700
From: Terry Lambert <tlambert2@mindspring.com>
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To: Attila Nagy <bra@fsn.hu>
Cc: freebsd-arch@freebsd.org, freebsd-net@freebsd.org
Subject: Re: HEADS UP: ALTQ integration developer preview
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Attila Nagy wrote:
> > > the "em" driver (if "gx" is already in the initial plan), because it
> > > reportedly works better (for example I couldn't do NFS serving with UDP
> > > packets bigger than the MTU with that, while the "em" driver works OK).
> >
> > It *does* frag packets bigger than the MTU, right?
> 
> netstat didn't show any errors regarding to that. If I used an NFS
> readsize, smaller than the 1500 bytes MTU it worked (was slow, but
> worked).
> netstat's frag counters were increased.
> I couldn't use tcpdump (I had no bpf support) to see what happens on the
> wire...

Sending datagrams bigger than the MTU is a bad idea.

I would be real tempted to drop the packets and send "don't fragment"
ICMP responses to beat up anyone who abused UDP by sending larger
than the MTU.

I guess this is about Linux UDP NFS clients, in particular.

-- Terry

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