Date: Wed, 30 Apr 2008 19:02:04 +0100 From: "Bruce M. Simpson" <bms@FreeBSD.org> To: Bakul Shah <bakul@bitblocks.com> Cc: FreeBSD Net <freebsd-net@freebsd.org>, Julian Elischer <julian@elischer.org>, Kevin Oberman <oberman@es.net> Subject: Re: multiple routing tables review patch ready for simple testing. Message-ID: <4818B41C.3090500@FreeBSD.org> In-Reply-To: <4818B2B7.2070401@FreeBSD.org> References: <20080430172705.2E3275AD6@mail.bitblocks.com> <4818B2B7.2070401@FreeBSD.org>
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Bruce M. Simpson wrote: >> >> 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? >> > > It doesn't buy anything because there is still no 1:1 mapping -- the > link-layer destination address maps to an ifp, and multiple aliases > exist on the ifp. Let me qualify that further: You are talking about splitting network layer addresses onto their own logical interfaces, with the goal of having a 1:1 mapping for FIB resolution. This doesn't buy anything, because in IP, the previous hop never encodes the next-hop address it sends to -- it merely performs a lookup and forwards to you; your MAC address is the same for every IP address you have on the link, therefore it is not a unique identifier. UNLESS you use a separate MAC address for every IP alias which you add, in which case, you are merely pushing the mapping elsewhere in the stack; it actually adds more complexity in this case.
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