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[ScreenOS] Receiving IP Spoof alarms

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Article ID: KB5780 KB Last Updated: 22 Jun 2010Version: 4.0
Summary:
Receiving IP Spoof alarms on firewall
Symptoms:
  • Receiving IP Spoof alarms
  • Alarm event logs show IP Spoof message
  • Alarm event message: ATTACK ALARM:  IP Spoof from x.x.x.x/xx to x.x.x.x/xxxx protocol TCP (trust) (xx/xx/xx xx:xx:xx)
Solution:

An IP Spoof from the trust side is typically a misconfigured system.  The firewall sees an IP address that is already has in its ARP table or is not found in its route table and reports an IP Spoof. 
 
Determine if there is a PC with a misconfigured NIC, and change this to reflect the correct network address.

If the message says it's coming from untrust, then it is a legitimate IP Spoof from someone on the outside.  The firewall would detect this, and drop it.  Here's an example of someone trying to spoof from the outside:

05/30/2002 12:43:14 ATTACK ALARM:  IP Spoof from 192.168.10.9/137 to 10.10.10.13/137 prot UDP (untrust)


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