Date: Wed, 30 Apr 2008 10:27:05 -0700 From: Bakul Shah <bakul@bitblocks.com> To: Julian Elischer <julian@elischer.org> Cc: FreeBSD Net <freebsd-net@freebsd.org>, "Bruce M. Simpson" <bms@FreeBSD.org>, Kevin Oberman <oberman@es.net> Subject: Re: multiple routing tables review patch ready for simple testing. Message-ID: <20080430172705.2E3275AD6@mail.bitblocks.com> In-Reply-To: Your message of "Tue, 29 Apr 2008 13:42:03 PDT." <4817881B.7010409@elischer.org>
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On Tue, 29 Apr 2008 13:42:03 PDT Julian Elischer <julian@elischer.org> wrote: > > Interfaces are not however assigned to FIB instance. each FIB may > contain entries for each interface, and by default they do, but you > can delete teh entries associated with a particular interface from > a particular FIB so that fib will never use that interface. > > An interface may however be present in entries from multiple FIBs > in which case the INCOMING packets on that interface need to > be disambiguated with respect to which FIB they belong to. 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? 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. 3) When a local packets needs to be sent, which FIB gets it? Does setfib decides that? If there a default FIB? > This is a job for an outside entity (from the fibs). > In this case a packet classifier such as pf or ipfw is ideal > for the job. providing an outside mechanism for implementing > whatever policy the admin wants to set up. I believe having to use pf/ipfw will slow things down a bit so the question is what does associating an interface with multiple FIBs buy you? > if you have several alias addresses on an interface it is possible > that some FIBS know about some of them and others know about other > addresses. New addresses when added are added to each FIB and > whatever is adding them shoudl remove them from the ones that don't > need it. This may change but it fits in with how the current code > works and keeps the diff to a manageable size. > (and it suits what I need for work where a route manager daemon > knows to do this.) Wouldn't it make sense to treat each alias as on a separate logical interface? Then each logical interface belongs to exactly one FIB. On input you decide which logical inteface a packet arrived on by looking at its destination MAC address. That reduces confusion quite a bit, at least in my mind! What does doing more than this buy you?
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