On Wed, Jul 26, 2017 at 12:16:17AM +0000, Acee Lindem (acee) wrote: > I must admit that I had always thought that the source-routing paradigm in > draft-troan-homenet-sadr-01.txt was backward with the destination address > Longest Prefix Match (LPM) being done prior to the source address lookup. > Rather I think if were going to standardize in the RTG WG, it should be > the FIB organization described in section 3 of > draft-ietf-rtgwg-enterprise-pa-multihoming-01.txt. Note that doing the > source address lookup first maps directly to the PA multi-homing > use-case.
I see both a misunderstanding and an internal contradiction here. The misunderstanding is that enterprise-pa-multihoming is describing source-first RIB or protocol behaviour. It isn't - it's describing a destination-first RIB and a source-first FIB translation. Conversely, rtgwg-dst-src-routing isn't specifying a dst-first FIB, see below. This is also where this contradicts itself; the PA multi-homing use-case does *not* map to source-first. If it did, you wouldn't need the route duplication. In fact, the PA multihoming case -- just like homenet -- needs destination-first to get local connectivity up and running. Also, and very importantly, I really don't want to go around telling people how to run their FIBs. It doesn't matter, as long as they're forwarding packets in a manner confirming to the spec. This is also why I've moved A.1 and A.2 into the appendix on the -05 rev of the draft; I felt these suggestions on how to efficiently operate this on a source-first (A.2) or destination-first (A.1) FIB are most appropriate in an appendix. On Wed, Jul 26, 2017 at 08:52:53PM +0000, Acee Lindem (acee) wrote: > I believe the tables could be similarly collapsed giving source address > higher precedence than destination address. Do you disagree? They can be, this is described in appendix A.2. of dst-src-routing-05. This does result in more duplicated routes than the other way around, but it's a perfectly viable implementation choice. That said, it makes no sense to use this in routing protocol signaling, or even the RIB. This is a FIB implementation detail. For protocol and RIB operation, destination-first-with-fallthrough provides the semantics that make the most sense to describe a network and get it up and running -- even if all of the routers have source-first FIBs and perform this translation step on installing a route. Cheers, -David _______________________________________________ rtgwg mailing list [email protected] https://www.ietf.org/mailman/listinfo/rtgwg
