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## Re: [Fwd: [Fwd: I-D ACTION:draft-ietf-rtgwg-microloop-analysis-00.txt]]

 Subject: Re: [Fwd: [Fwd: I-D ACTION:draft-ietf-rtgwg-microloop-analysis-00.txt]] Russ White Thu, 28 Jul 2005 08:29:13 -0400
 I'm completely confused about what you are saying here. We are talking about B wanting to send traffic to C, right? In BOTH cases there is a loop. Clearly so in the first case, since there is no other path than through B. But in the second case there is also a loop because of ECMP. If ANY ECMP path may loop then you have to consider it a loop. Then you suggest changing the B-D cost to 25. Again in BOTH cases there is loop. I don't know what you are trying to show here. So, this is part of the problem--what do you mean by "loop?" Do you mean D has an alternate path that does not go through B, or do you mean D would not send traffic via B to get to C given the current metrics? Those are two different definitions, and I've not figured out which one the draft is using. I _think_ the draft "wants to mean" that the first is a loop free path, and the second is a "downstream neighbor," but the formula's don't seem to work this way. However if you changed the cost of B-D to 51 THEN it becomes interesting. Case 1 is clearly a loop, but case 2 is not. ```>> A-(25)-B-(25)-C >> | | >> | (50) >> | | >> +-(25)-D >> >> A-(25)-B-(25)-C >> | | >> (50) | >> | | >> D-(75)-+ ```In neither case is D a downstream neighbor (since the cost from D to C is > cost from B to C). ```But consider LFAs we have an LFA if D_opt(N, D) < D_opt(N, S) + D_opt(S, D) or in this case if D_opt(D, C) < D_opt(D, B) + D_opt(B, C) But in case 1 D is NOT an LFA D_opt(D, C) = 75 (DABC) D_opt(D, B) = 50 (DAB) D_opt(B, C) = 25 (BC) hence 75 !< 50 + 25 whereas in case 2 D IS an LFA D_opt(D, C) = 75 (DC) D_opt(D, B) = 51 (DB) D_opt(B, C) = 25 (BC) hence 75 < 51 + 25 ```I see, you're counting on the looped path showing up as an alternate lower cost path to the neighbor itself. In other words, this could be simlified to if there is a path with lower cost to the neighbor through some other path, then the path through the neighbor must be a loop. ```Then why not just say so? :-) ```The draft is very confusing, and doesn't really explain the principle being used here very well at all.... ```:-) Russ _______________________________________________ Rtgwg mailing list [email protected] https://www1.ietf.org/mailman/listinfo/rtgwg ```
 Current Thread [Fwd: [Fwd: I-D ACTION:draft-ietf-rtgwg-microloop-analysis-00.txt]], Russ White Message not available Message not available Message not available Message not available Message not available Message not available Message not available Re: [Fwd: [Fwd: I-D ACTION:draft-ietf-rtgwg-microloop-analysis-00.txt]], Russ White Re: [Fwd: [Fwd: I-D ACTION:draft-ietf-rtgwg-microloop-analysis-00.txt]], mike shand Re: [Fwd: [Fwd: I-D ACTION:draft-ietf-rtgwg-microloop-analysis-00.txt]], Russ White <= Re: [Fwd: [Fwd: I-D ACTION:draft-ietf-rtgwg-microloop-analysis-00.txt]], Alia Atlas