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Date:      Wed, 6 Dec 2000 08:15:49 +0100
From:      Sebastiaan van Erk <sebster@sebster.com>
To:        freebsd-security@freebsd.org
Subject:   rx list
Message-ID:  <20001206081549.A49341@sebster.com>

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Good morning everybody!!

I have a question. Yesterday two production firewalls were (probably)
attacked using a DoS attack.

One of them is running 4.1.1-RELEASE, the other is running 3.4-STABLE.

I get these kind of messages in the syslog of both machines.

Dec  6 00:09:43 hobbes /kernel: Out of mbuf clusters - adjust NMBCLUSTERS or inc
rease maxusers!
Dec  6 00:09:43 hobbes /kernel: xl2: no memory for rx list -- packet dropped!
Dec  6 00:09:43 hobbes /kernel: xl1: no memory for rx list -- packet dropped!

I checked on the net, but it seems to suggest that systems after 3.2 and 4.0
should be safe. Also I don't see any patches.

How likely is it that this is a DoS attack (note that we also get the message
on the internal interface!)? And how do I go about fixing it? (I can increase
maxusers and NMBCLUSTERS, but then how do I know it's not going to happen
again?).

Thanks in advance,
Sebastiaan van Erk


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