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Date:      Mon, 15 Jan 2001 22:40:11 -0800
From:      "Crist J. Clark" <cjclark@reflexnet.net>
To:        Yonatan Bokovza <Yonatan@xpert.com>
Cc:        freebsd-security@FreeBSD.ORG
Subject:   Re: FW: ICMP fragmentation required but DF set problems.
Message-ID:  <20010115224011.G97980@rfx-64-6-211-149.users.reflexco>
In-Reply-To: <00BF97DD9F3FD311AB860060084E50DD782F24@exchange.xpert.com>; from Yonatan@xpert.com on Mon, Jan 15, 2001 at 08:45:49PM %2B0200
References:  <00BF97DD9F3FD311AB860060084E50DD782F24@exchange.xpert.com>

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On Mon, Jan 15, 2001 at 08:45:49PM +0200, Yonatan Bokovza wrote:
> hey,
> This was just up on BugTraq. Can anyone add information
> to the topic?

There are much more interesting attacks available to anyone who cares
to try. I haven't read the PMTU discovery RFCs for a while. Can't say
if this attack is practical on an RFC-compliant IP stack or if there
are ways to defend against it without breaking the RFCs.

If you are paranoid, you can turn off PMTU discovery,

  # sysctl -w net.inet.tcp.path_mtu_discovery=0

-- 
Crist J. Clark                           cjclark@alum.mit.edu


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