Hi Les, Thanks for your response. Please see inline..
On Thu, Feb 17, 2022 at 8:56 PM Les Ginsberg (ginsberg) <[email protected]> wrote: > Muthu – > > > > RFC 7775 is defining preference rules between routes of different types – > it is NOT discussing preference rules within a (set of) route types that > have the same preference. > Ok, but RFC7775 says "Note that all types of routes listed for a given preference are treated equally". How is that to be interpreted when there is an L1 intra-area route of metric a and an L1 external route of metric b for the same IPv6 prefix during comparison? Regards, Muthu > Such a discussion is out of scope. > > > > Use of “lowest cost” is part of the well known Dijkstra Shortest Path > First (SPF) algorithm – though there are many example of constrained SPF > calculations that incorporate attributes other than cost in the choice of > “best path”. > > All of this is out of scope for RFC 7775. > > > > Les > > > > *From:* Lsr <[email protected]> *On Behalf Of * Muthu Arul Mozhi > Perumal > *Sent:* Thursday, February 17, 2022 6:49 AM > *To:* lsr <[email protected]> > *Subject:* [Lsr] Preference among IS-IS IPv6 route types > > > > Hi, > > > > Need some clarification on the preference among IS-IS IPv6 route types > described in RFC7775 section 3.4 and RFC5308 section 5. > > > > RFC7775 places L1 intra-area routes and L1 external routes at the same > preference level and says that all types of routes listed for a given > preference are treated equally. There is no mention of metric. > > <snip> > > This document defines the following route preferences for IPv6 routes > advertised in TLVs 236 or 237. Note that all types of routes listed > for a given preference are treated equally. > > 1. L1 intra-area routes; L1 external routes > > 2. L2 intra-area routes; L2 external routes; L1->L2 inter-area > routes; L1-L2 external routes; L2-L2 inter-area routes > > 3. L2->L1 inter-area routes; L2->L1 external routes; L1->L1 inter- > area routes > </snip> > > > > RFC5308 however says: > > <snip> > > If multiple paths have the same best preference, then selection > occurs based on metric. > > </snip> > > > > It is not clear whether metric is to be used for selection among L1 > intra-area and external routes or is to be used for selection only with a > given route type. Can someone please clarify? > > > > Regards, > > Muthu >
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