Date: Fri, 14 May 1999 15:46:19 -0600 From: Brett Glass <brett@lariat.org> To: Harold Gutch <logix@foobar.franken.de>, Matthew Dillon <dillon@apollo.backplane.com> Cc: Jared Mauch <jared@puck.Nether.net>, Thamer Al-Herbish <shadows@whitefang.com>, security@FreeBSD.ORG Subject: Re: Forwarded from BUGTRAQ: SYN floods against FreeBSD Message-ID: <4.2.0.37.19990514154319.04610b80@localhost> In-Reply-To: <19990514225001.A22317@foobar.franken.de> References: <4.2.0.37.19990514133829.0461e220@localhost> <199905140438.VAA97604@apollo.backplane.com> <Pine.BSF.4.05.9905131824250.267-100000@rage.whitefang.com> <4.2.0.37.19990513161529.00c1e3f0@localhost> <Pine.BSF.4.05.9905131824250.267-100000@rage.whitefang.com> <4.2.0.37.19990513202450.0444fca0@localhost> <199905140438.VAA97604@apollo.backplane.com> <19990514072546.A20779@foobar.franken.de> <4.2.0.37.19990514133829.0461e220@localhost>
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At 10:50 PM 5/14/99 +0200, Harold Gutch wrote: >On Fri, May 14, 1999 at 02:05:51PM -0600, Brett Glass wrote: > > Any technique that requires the originator to receive your > > SYN-ACK and generate a specific response before you commit > > resources is acceptable. Heck, you don't even really need > > a cryptographically strong hash for this. Is Linux really > > doing one MD5 per SYN? If so, I can think of a few other > > techniques that would give us a speed advantage. We'd be > > able to beat them in the benchmarks while still providing > > good protection against SYN flooding. > > >Ah, that's a very good point, I never thought of the >speed-question. Actually, it turns out that the Linux approach requires a minimum of two MD5's -- one at the time of the SYN and again when the SYNner responds to the SYN-ACK. I think there are a total of three in their algorithm. This gives us a chance to gain a LOT of speed if we can avoid doing all those MD5s. >But you are right - back to the original topic. I checked my >2.2.8 boxes and flooded them with 1 Million SYN packets taking >about 1 minute, so that's (roughly) 16000 SYNs per second. I did >not manage to kill them with this. It may also depend on the complexity of your routing tables. --Brett To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-security" in the body of the message
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