SYN floods (was: does history repeat itself?)

Fri Sep 13 20:49:45 UTC 1996

     Joel,

        If I understand what you are stating is that the filtering which I 
     have described could work for dial-up users, but not for customers 
     which have a dedicated "leased" line into the network. You state that 
     this is not possible due to the CPU overhead that the filtering of 
     each packet creates.

        Out of curiosity, what would the CPU usage be on a typical router 
     in your installation??? Also, do we know what the overhead is for a 
     single filter at the ingress on a router such as a Cisco???

     Pat R. Calhoun                                e-mail: pcalhoun at usr.com 
     Project Engineer - Lan Access R&D                phone: (847) 933-5181 
     US Robotics Access Corp.

______________________________ Reply Separator _________________________________
Subject: Re: Re[2]: SYN floods (was: does history repeat itself?)
Author:  Joel Gallun <joel at linux.wauug.org> at Internet
Date:    9/12/96 2:52 PM

What you propose is a Good Thing (tm), but I don't think it's sufficient. 
It still doesn't protect the 'net from antisocial behavior perpetrated by 
someone who has penetrated a system with dedicated access to the 'net. It 
seems like it would still be necessary for anyone selling dedicated access 
to install Good Neighboor (tm) anti-spoofing filters on their inbound 
interfaces (which probably requires MIPS that the routers in the field 
don't have).

Regards,

Joel

On Thu, 12 Sep 1996, John G. Scudder wrote:

> At 1:44 PM -0400 9/12/96, Curtis Villamizar wrote:
> >I agree with you completely -- sort of.  Only problem is there are
> >thought to be some 3,000 dial access providers.  Many of them barely 
> >know what a TCP SYN is, let alone why they need to block ones with
> >random source addresses and how.  Unless of course you are 
>                                    ^^^^^^^^^^^^^^^^^^^^^^^^
> >volunteering to explain it and help them.  Thanks in advance.  :-) 
>  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> 
> Curtis, this is a great point.  USR and other NAS vendors are actually in a 
> great position to do exactly this, by changing their boxes to block random 
> addresses *by default* on dial-up ports.  This is of course exactly the
> point Vadim and others keep making, and of course as they point out there 
> ought to be a knob to disable it if desired.
> 
> Insofar as guys who "barely know what a TCP SYN is" are unlikely to twist
> the knobs, defaulting filtering to "block spoofed addresses" seems like the 
> best and maybe only way to get them to do it.
> 
> How about it, USR &al?
> 
> --John
> 
> --
> John Scudder                        email:  jgs at ieng.com
> Internet Engineering Group, LLC     phone:  (313) 669-8800 
> 122 S. Main, Suite 280              fax:    (313) 669-8661
> Ann Arbor, MI  41804                www:    http://www.ieng.com 
> 
> 

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Date: Thu, 12 Sep 1996 14:52:10 -0400 (EDT)
From: Joel Gallun <joel at linux.wauug.org>
To: "John G. Scudder" <jgs at ieng.com>
cc: curtis at ans.net, Pat Calhoun <pcalhoun at usr.com>, nanog at merit.edu
Subject: Re: Re[2]: SYN floods (was: does history repeat itself?)
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