Re: Defending against SYN-flood DoS attacks

[InfoSec News <isn () c4i org>]

Forwarded from: Russell Coker <russell () coker com au>

On Mon, 27 Aug 2001 14:54, InfoSec News wrote:

> http://www.theregister.co.uk/content/5/21284.html
>
> By Thomas C Greene in Washington
> Posted: 25/08/2001 at 00:39 GMT
>
> With this difficulty in mind, TechMavens' Ross Oliver decided to
> benchmark several hardware solutions, all in roughly the same
> price range, using a homebrew kit to simulate SYN floods against
> them. He released his results at last week's USENIX Security
> Symposium in Washington.
>
> He established a baseline for his test server (Apache over Red Hat
> 7.1), which, when unprotected, crashed at 100 SYNs/sec. The worst
> performers were the Cisco PIX firewall and Checkpoint's Firewall-1
> equipped with the SYNDefender module.
>
> The Cisco kit showed no advantage whatsoever, crashing at the
> baseline 100 SYNs/sec. Firewall-1 showed only marginally better
> results, breaking down (i.e., dropping connections) at a lame 500
> SYNs/sec, which can be exceeded by only two or three boxes
> connected by T1, cable or DSL lines.
>
> It's fair to note that while one expects at least some protection
> from any firewall, the Cisco kit isn't marketed for SYN flood
> protection as the Checkpoint kit obviously is.
>
> Netscreen's Netscreen-100 fared better, breaking down after 14,000
> SYNs/sec for a 28-fold performance improvement at roughly the same
> price.
>
> Only the Top Layer AppSafe switch exceeded the test's limits,
> showing no sign of stress while sustaining 22,000 SYNs/sec, the
> maximum Oliver could throw at it with his rig. This would work out
> to about one dollar per SYN during a fairly severe attack, which
> strikes us as rather economical protection.

It would be nice if such comparisons compared more common setups.  
Probably the most commonly used protection against SYN flooding is
that in the Linux kernel, it would be interesting to see how that
performs.  I believe that Solaris has some similar protection which
would be useful to compare with it.

Then there's thew capabilities of load balancers that aren't designed
to handle this, such as Cisco Localdirector's.  While such devices
aren't specifically designed to fend of SYN attacks the fact that they
don't establish a connection to the real server until after they have
completed the 3 way handshake with the client will result in the SYN
attack not hitting the client (and hopefully a LocalDirector can deal
with such things better than an unprotected server).


Russell Coker



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