ipfw workaround for syn-loop attack, FreeBSD 2.2.5-STABLE

From: Robert Watson (robertat_private)
Date: Thu Nov 20 1997 - 15:15:22 PST

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    Adding a rule for the interface denying packets from oneself appears to
    defend against the new attack.
    
    This rule worked:
    
    03001 deny ip from 128.2.91.57 to 128.2.91.57 via ed0
    
    Where 128.2.91.57 is the host's IP address on device ed0.
    
    This presumably works on other versions of FreeBSD, and other systems with
    ipfw/ipfirewall installed on them.  As always, if you are not familiar
    with ipfw and don't know how it works, don't use this unless you are on
    the console the first time!
    
    Adding this to rc.firewall on FreeBSD is also a good idea.  Multi-homed
    hosts require one entry per device, needless to say.
    
      Robert N Watson
    
    Junior, Logic+Computation, Carnegie Mellon University  http://www.cmu.edu/
    Network Administrator, SafePort Network Services  http://www.safeport.com/
    robertat_private rwatsonat_private http://www.watson.org/~robert/
    



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