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SonicWall Alert - Intrusion Prevention - IP spoof dropped

Posted on 2009-05-07
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I need help interpreting this alert log coming from my Firewall. I need to figure out what this Intrusion Prevention is.

At least 20 of these per hour:
Time: 05/07/2009 11:26:03
Priority: Alert
Category: Intrusion Prevention
Message: IP spoof dropped
Source: 169.254.99.56, 137, LAN
Destination: 10.83.32.8, 137, WAN, ws100098.bcr.local
Notes: MAC address: 00:02:b3:d8:bd:a2

This SonicWall is connected via site-to-site VPN to another office.
Local Network: 10.81.0.1 / 255.255.0.0
Remote Network via site-to-site VPN: 10.83.0.1 / 255.255.0.0

Please correct me if I'm wrong, but for now, my interpretation of this is that we have a machine on our LAN with IP 169.254.99.56, trying to communicate with another machine in our remote office with IP 10.83.32.8.

How do I locate this local machine with this 169.xx.xx.xx IP address, and why is it being treated as an intrusion??
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Question by:pzozulka
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thetmanvn earned 2000 total points
ID: 24329652
Hi pzozulka,

1./ The Internet Assigned Numbers Authority (IANA) has reserved 169.254.0.0-169.254.255.255 for Automatic Private IP Addressing. If the computer can't get ip from DHCP, APIPA provides an address that is guaranteed not to conflict with routable addresses.

So that was one of your box could not get IP from your DHCP.
According to the MAC Address of source IP, it means packet come from a box with Intel Network Interface Card.
If you have a port managed switch, you can identify which port had this MAC come to.

2./ It was treated as an IP Spoof, of course because Sonic Wall knew which IP subnet of your LAN, but the source IP coming from LAN was not in this range, so it will detect that was spoof IP and block by IPS system.
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by:pzozulka
ID: 24330645
Perfect answer. Tracked down the IP address to one of our local Domain Controllers. However the  IP 169.254.99.56  belongs to a DISABLED Network Connection, so I'm not sure how it is communicating. It is  trying to communicate with a workstation in our other office. Any thoughts how is it communicating especially if it says network cable unplugged?

Thanks for your help, you already solved 99% of my problem.
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by:thetmanvn
thetmanvn earned 2000 total points
ID: 24333600
Hi pzozulka,

It's not a DISABLED network, just are UNPLUGGED. And as I see as maybe your Main (Virtual) Interface did has some routing function here and the UNPLUGGED NIC try to broadcast to use Netbios name service via the Main (Virtual) Interface, and one of them was go through SonicWall to your remote office and it was block.

Hope this help.
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