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Date:      Tue, 25 Jan 2000 10:08:12 +0200
From:      Ruslan Ermilov <ru@ucb.crimea.ua>
To:        Mike Tancsa <mike@sentex.net>
Cc:        questions@FreeBSD.org
Subject:   Re: rule -1 on ipfw
Message-ID:  <20000125100812.A32413@relay.ucb.crimea.ua>
In-Reply-To: <3.0.5.32.20000124131838.01ce4e10@staff.sentex.ca>; from Mike Tancsa on Mon, Jan 24, 2000 at 01:18:38PM -0500
References:  <3.0.5.32.20000124131838.01ce4e10@staff.sentex.ca>

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On Mon, Jan 24, 2000 at 01:18:38PM -0500, Mike Tancsa wrote:
> 
> What would trigger something like this in my logs
> 
> ipfw: -1 Refuse TCP 209.226.155.246 my.ip.address. in via fxp0 Fragment = 185
> 
> when I have
> 
> 00100 166968  24813244 allow ip from any to any via lo0
> 00200      0         0 deny ip from any to 127.0.0.0/8
> 00250      0         0 deny log logamount 21000 tcp from any to any 8007 in
> recv fxp0
> 65000 826281 482465357 allow ip from any to any
> 
> Its a STABLE box as of today.
> 
This is documented in the ipfw(8) manpage:

: There is one kind of packet that the firewall will always discard, that
: is an IP fragment with a fragment offset of one.  This is a valid packet,
: but it only has one use, to try to circumvent firewalls.

See RFC1858 (Security Considerations for IP Fragment Filtering) for details.


Cheers,
-- 
Ruslan Ermilov		Sysadmin and DBA of the
ru@ucb.crimea.ua	United Commercial Bank,
ru@FreeBSD.org		FreeBSD committer,
+380.652.247.647	Simferopol, Ukraine

http://www.FreeBSD.org	The Power To Serve
http://www.oracle.com	Enabling The Information Age


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