I'd love to test this out.. If it could do full gigabit line rate with random ips that would be soooooooo nice :> We wouldn't have to have so many routers any more!! :) Paul xerox@foonet.net http://www.httpd.net -----Original Message----- From: David S. Miller [mailto:davem@redhat.com] Sent: Monday, June 09, 2003 1:45 AM To: xerox@foonet.net Cc: sim@netnation.com; fw@deneb.enyo.de; netdev@oss.sgi.com; linux-net@vger.kernel.org Subject: Re: Route cache performance under stress From: "CIT/Paul" <xerox@foonet.net> Date: Sun, 8 Jun 2003 19:55:58 -0400 The problem with the route cache as it stands is that it adds every new packet that isn't in the route cache to the cache, say you have A denial of service attack going on, OR you just have millions of hosts going through the router (if you were an ISP). We perform now rather acceptibly in such scenerios. Robert Olsson has demonstrated that even if the attacker could fill up your entire bandwidth with random source address packets, we'd still provide 50kpps routing speed. And this can be made much higher because the performance limiter is the routing cache GC which isn't tuned properly. It can't keep up because it doesn't try to purge the right amount entries each pass. All the performance problems I've seen have been algorithmic or outright bugs. Bad hash functions and limits in how big the FIB hash tables would grow. And what's left is fixing GC. There is nothing AT ALL fundamental about a routing cache that precludes it from behaving sanely in the presence of a random source address DoS load. Absolutely NOTHING. This can stifle just about any linux router with a measly 10 megabits/second of traffic unless Not true, that happens because of BUGs. Not because routing caches cannot behave sanely in such situations. The router is tuned up to a large degree (NAPI, certain nics, route cache timings, etc.) and even then it can still be destroyed no matter what And today, this is because of BUGs in how the GC works. You can design the GC process so that it does the right thing and recycles only the DoS entries (those being very non-localized). You should interact with Robert Olsson who has been doing tests on the effect of gigabit rate full-on DoS runs where every packet creates a new routing cache entry. Franks a lot, David S. Miller davem@redhat.com - : send the line "unsubscribe linux-net" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
