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Thread: IP Spoof

  1. February 11th, 2004, 02:04 PM #1
    dinowuff
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    IP Spoof

    On a simple NT4 network lives a Sonic Wall Firewall. The logs indicate a IP Spoof detected and dropped. The source IP address is a private address and the MAC address is listed.

    IP spoof detected - Source:192.168.81.1, 137, LAN - Destination:192.168.80.2, 137, WAN - MAC address: 00.0D.56.34.64.8B -

    Here's my dilemma: The private range is not on my network, I'm using 10. So I assume that someone (Probably a MCSE - Sorry about that) has configured a device incorrectly and plugged into the LAN.

    I have scanned the network for the MAC address with no luck. Address not found!

    I'm not too worried about this but I would like to find out what's going on - any suggestions?

    Thanks,
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  2. February 11th, 2004, 02:19 PM #2
    SirDice
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    On what interface does this spoof get detected? That should give you a clue if it's originating from the inside or the outside. If it's from the outside (the Internet) you can safely ignore it since your firewall is dropping them.
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  3. February 11th, 2004, 03:04 PM #3
    dinowuff
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    SirDice:

    Since the source and destination are private addresses and the mac address is listed, wouldn't the device have to be on the inside?
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  4. February 11th, 2004, 03:55 PM #4
    SirDice
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    It should be easy to see on your firewall. I am assuming the firewall has at least 2 NIC's. It wouldn't be of much use if it didn't. Therefor it should be easy to find out where it comes from.

    As for the private addresses, it could be possible (under certain conditions). I know for a fact that private addresses as a source will get routed over the Internet. Private destination addresses shouldn't but maybe somebody screwed up who's on the same segment as you.
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  5. February 11th, 2004, 05:24 PM #5
    netman4ttm
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    www.komododigital.com

    Go to their web site download newt.

    Install and you will find your NIC
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  6. February 12th, 2004, 04:59 PM #6
    dinowuff
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    OK, the issue was a Cisco VPN Client. Vendor plugged into the network and launched his VPN software, the private address' showing as "Spoof IP's" were the virtual adaptor and virtual gateway.

    This poses a few different questions, I'll try to address them in a later post. Thanks for the help.
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