Hi Tony, Thank you for your explanation below. Actually what you wrote is pretty easy to digest unless some call them "stubborn" head-ends will continue to spread evenly traffic across all three South, Central and North paths.
But my root of hesitation is different. In the below if all headends cooperate traffic from A to B can be consolidated on the North path. But I see no connection nor hint for also consolidating traffic from B to A to the North path. Traffic B to A may have completely different characteristics then traffic from A to B. And unless we are talking UDLR freeing links must be done bidirectionally - wouldn't you agree ? To be specific if headends in the A to B direction will consolidate traffic on North and Central links and nodes B to A on Central and South you would rather not end up in position to bring down any of the three links. Assume cost (in terms of power cost) is the same across all links. Many thx, Robert Having a fully distributed solution is always cool, but as we discussed > offline I do have lots of hesitation that specific links or line cards > could be drained *bidirectionally* in a distributed CSPF computation > fashion. Clearly you have spent loads of time more than me making sure it > does work so I am not questioning that. Just expressing my hesitation. > > > Let’s see if we can address it. > > Let’s imagine a network where we have three paths from point A to B. > Let’s arbitrarily call them North, South, and Central. Suppose that > initially traffic is evenly divided amongst them. > > Let’s further imagine that all head-ends understand that the goal is to > consolidate traffic. Suppose that we have many different LSPs and many > different head-ends doing the path computation. Further, suppose that > traffic levels have dropped enough that traffic can be consolidated. > > Pick any head-end. It goes to optimize an LSP. What does it do? It > wants to consolidate traffic. If the paths are not equivalent, then it’s > obvious that it should consolidate on the least cost path. If the paths > are equivalent, then it can arbitrarily pick one. Let’s say that it moves > traffic from Central to North. > > Now, some other head-end goes to optimize a different LSP and it sees that > the North path has more traffic. It then shifts its traffic to the North > as well, again trying to consolidate. This continues until the path is > full. Presumably the remaining traffic further consolidates and the one of > the two paths can be put into power sleep. > > The only time that this could possibly be an issue is if two systems made > simultaneous opposite and offsetting decisions, and there are no other > changes going on, and they continue to remain in lock-step. Given the > thousands of different LSPs in a common network, this seems exceedingly > unlikely. Right up there with all of the oxygen in the room collecting in > the upper northwest corner. > >
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