Date: Sun, 01 Jul 2001 10:00:19 -0700 From: Bakul Shah <bakul@bitblocks.com> To: Wes Peters <wes@softweyr.com> Cc: Ruslan Ermilov <ru@FreeBSD.org>, Deepak Jain <deepak@ai.net>, net@FreeBSD.org, hackers@FreeBSD.org Subject: Re: fastforwarding? Message-ID: <200107011700.NAA07500@tonnant.cnchost.com> In-Reply-To: Your message of "Wed, 27 Jun 2001 22:39:20 MDT." <3B3AB4F8.184A2EFE@softweyr.com>
next in thread | previous in thread | raw e-mail | index | archive | help
> > What does the fastforwarding option do that the normal forwarding option > > doesn't? > The description there isn't very forthcoming. fastforwarding caches > the results of a route lookup for destination addresses that are not > on the local machine, and uses the cached route to short-circuit the > normal (relatively slow) route lookup process. The packet flows > directly from one layer2 input routine directly to the opposing > layer2 output routine without traversing the IP layer. You do have to look at the destination ip address so strictly speaking the cache belongs to the ip "layer". I haven't looked at this fastforwarding code but it likely complicates route adding/deleting at you have to look at it for *any* route add/delete. For example, for dest addr 1.2.3.4, you cached the result of route lookup (which may be 1.2.x.x/16) and now a route for 1.2.?.x/24 is added. You may have to invalidate the cache entry since the new route may have to be used. Similarly for deletes. Even the old single entry cache in the std 4.4bsd had/has a related bug. IMHO you are better off using a recent route lookup algorithm than messing with caches. The PATRICIA tree algorithm is what 33 years old now? There has been a lot of research done in this area in the last few years. On a modern machine with some of the recent algorithms you should be able to easily do a lookup in a just a few memory accesses. The changeover is not easy and quite pervasive in the networking code but long overdue. If anyone decides to do this, please make the changes so that any algorithm can be pluuged in. To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?200107011700.NAA07500>