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Date:      Mon, 12 Nov 2001 08:59:47 -0500
From:      "Wade Majors" <wade@ezri.org>
To:        <security@freebsd.org>
Subject:   Filtering packets based on incoming address [ack. plaintext now]
Message-ID:  <001201c16b82$4da9d1e0$9700a8c0@ezri>

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When reading through http://www.sans.org/top20.htm the other day, I
noticed G5. It talks about how packets can be "spoofed" to really target
a machine on my network and not the gateway.

I added these rules to my /etc/ipfw.rules file:

# block spoofed packets going to private network
add 00001 deny ip from any to 192.168.0.1/24 in recv fxp0
# block sppoofed packets going to cable modem
add 00002 deny ip from any to 10.97.48.1 in recv fxp0

These are the only things before natd, which is rule 00050.

In the few days I've had them in; it hasn't caught anything, so I'm
going to assume this isn't breaking anything legitimate. The question
is: is this the right way to check for this stuff, anyway? Should I even
worry about this since my network using private IPs?

-Wade







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