Date: Fri, 02 May 2008 11:02:27 -0700 From: Julian Elischer <julian@elischer.org> To: John Hay <jhay@meraka.org.za> Cc: FreeBSD Net <freebsd-net@freebsd.org> Subject: Re: multiple routing tables review patch ready for simple testing. Message-ID: <481B5733.7020503@elischer.org> In-Reply-To: <20080502090200.GA57055@zibbi.meraka.csir.co.za> References: <20080430172705.2E3275AD6@mail.bitblocks.com> <4818BC79.40605@elischer.org> <20080502090200.GA57055@zibbi.meraka.csir.co.za>
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John Hay wrote: >>> This confuses me.... >>> >>> The whole point of a FIB is to decide the *next* hop for a >>> given input packet. So questions. >>> 1) A packet arrives on an interface. If this interface is >>> associated with more than one FIB, which FIB does it get >>> given to? >>> >> which ever one you select, using the policy of your choice. >> >> that's what policy routing is about. >> if you don't WANT policy based routing, dont turn it on. >> >> >> >>> 2) If that decision is taken by a a packet 'classifier', >>> isn't it in effect doing the job of a FIB (deciding the >>> next hop, which happens to be a local FIB)? Recall that >>> basically a packet passes from a FIB to another FIB until >>> it gets to its eventual destination. >> the packet classifier selects a FIB which in turn implements a >> particular routing decision tree. >> In the degenerate case where a FIB has only one route >> then you are correct, but there are technical reasons why this is >> superior to just using a fwd rule in the firewall. > > The linux guys seems to have multiple fibs (or whatever they call them) > which they can chain together by giving them different priorities. The > effect seems to be that a packet will be matched through the highest > priority fib to the lowest until a route match is found en then is used. > Will something like that be possible? I came across that kind of use > with the olsr guys. They let olsrd twiddle one of the higher priority > fibs and then put fallback routes in a lower priority fib. That way > olsrd can override a route (even the default route) and when olsrd > exists and deltes all its routes, the original ones are still in the > lower priority fib and will be used. no we are going to do the simple thing.. such enhancements can be done later if there is a call for it. We will just have a number of tables that you can associate a packet with at a number of points in its path. having another table as the 'default route' for a table (i.e. if you don't find something look in another table) is something that would be relatively easy to do, but I have not done it. > > John
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