From owner-freebsd-security  Sun Jul  8 18:13: 8 2001
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Date: Sun, 8 Jul 2001 20:13:02 -0500 (CDT)
From: Mike Silbersack <silby@silby.com>
To: <cjclark@alum.mit.edu>
Cc: Darren Reed <avalon@coombs.anu.edu.au>,
	Yonatan Bokovza <Yonatan@xpert.com>,
	"'freebsd-security@freebsd.org'" <freebsd-security@FreeBSD.ORG>
Subject: Re: FW: Small TCP packets == very large overhead == DoS?
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On Sun, 8 Jul 2001, Crist J. Clark wrote:

> On Mon, Jul 09, 2001 at 08:24:28AM +1000, Darren Reed wrote:
> > In some mail from Crist J. Clark, sie said:
> > > > What's most surprising is that there does not appear to be a documented
> > > > minimum, just as there is no "minimum MTU" size for IP.  If there is,
> > > > please correct me.
> > >
> > > The absolute minimum MTU for IP is 68 (RFC791).
> >
> > Yeah, enough for 64bytes of header options and 8 bytes of fragmented
> > data.  Not what I'd call a "useful" minimum.
>
> How about the 576 byte (IIRC) value? It's not really a network MTU,
> but all host must be able to handle datagrams of that size.

Looking at Darren's table, it seems like we could split the difference
between breaking things and allowing this to be abused. 256 sounds like a
good number.  Perhaps we should just make that the new minimum and not
worry any further.

Mike "Silby" Silbersack



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