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@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@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@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