The recent FreeBSD advisory regarding IP fragment denial-of-service 
attacks didn't mention whether or not an IP filter (ipfw or ipf) that 
drops all fragments is an adequate temporary work-around or not.

Does anyone who is familiar with the problem and attack know if something 
like the following would be a useful temporary work-around?

  ipfw add 1 deny ip from any to any fragment

Does the above drop the fragment and prevent reassembly buffer starvation?

Of course dropping ALL fragments like that will limit the connectivity of 
the host to hosts and networks where fragmentation occurs.  But, if the 
above DOES prevent the DOS, it may be a useful tradeoff to use it as a 
temporary work-around until kernels are patched (kernels with ipfw 
already enabled).

Aaron out.

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