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Re: SMURF amplifier block list
From: Dan Boehlke <dboehlke () mr net>
Date: Sat, 18 Apr 1998 14:50:56 -0500 (CDT)

On Sat, 18 Apr 1998, Alex P. Rudnev wrote:

What about people who didn't subnet their class B on the eight bit 
boundry, but made larger subnets instead?  What about the class B that 
doesn't appear to be subnetted at all?  What about supernetted class C 
networks?  A trailing .255 can be a valid host.
And what's worng? If they di nit subnet their B network, the tail of 
address should be .255 too.

If someone have particular .255 host - OK, you should not be able to ping 
it, not more. The small fee for the free-of-smurfing-from-your-network.

Why don't use the filter

 deny icmp any echo-request
Just now, USA's ISP seems to be absolutely helpless facing SMURF. A lot 
of networks do not block aroadcast echo-request's; no one even know how 
to trace thos 'echo-request' packets by their network... may be I am 
wrong, and it's because there is _a lot of ISP_ there, and even a few af 
them who do not know how to fight against SMURF compose a good backet - I 
do not know. 

Really; does anyone know any sucsessfull attempts to search for the 
smurfer? What penalty was provided for this hackers? Does exist some 
legitimate way to establish a lawsuite against them (when they'll be 
located - last is the only matter of qualification for their nearest ISP, 
not more).

I agree that ISPs are at the mercy of the smurfers.  At MRNet we have been
fighting an internal battle to get our customers to do the right things 
to block their ability to be used as a multiplier.  Its not just 
ignorance that keeps our customers from acting, it in some cases is their 

We have written SMURF detection software that uses cisco netflow exports 
to let us know when a SMURF is going on, either inbound or outbound.  
Before we had this, we didn't know how bad it was, we never saw the 
majority of the attacks or where our customer nets were being used as a 
multiplier.  We hope to automate a block.

Cisco is working on features to help with this problem.  They need to be 
given time to do it right.

We have implimented a filter that blocks broadcasts on our NSP border 
routers.  However this list only blocks the broadcast addresses in our 
CIDR blocks and on assigment boundries.  It has helped alot.

We can, as network administrators, clamp down this net so hard only the 
hackers would be able to use it.  Blocking all .255 traffic even just 
ICMP is a step too close to that.  Remember the distain for routers and 
hosts that made classfull assumptions when they were given an address?

Dan Boehlke, Senior Network Engineer                          M R N e t
Internet:  dboehlke () mr net                       A MEANS Telcom Company
Phone:  612-362-5814                  2829 SE University Ave. Suite 200
WWW: http://www.mr.net/~dboehlke/                Minneapolis, MN  55414

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