In mastering the lightning network, the following paragraph describes a facet of pathfinding

The pathfinding mechanism implemented in Lightning nodes is to first create a list of candidate paths, filtered and sorted by some function. Then, the node or wallet will probe paths (by attempting to deliver a payment) in a trial-and-error loop until a path is found that successfully delivers the payment.

Can we describe this version of probing in the context of LND and a classic mpp (base amp) payment?

For a classic mpp (no adulterations) are we using a real preimage hash (real described as one that has a preimage to be released upon successful htlc route established) for each of these trial-and-error attempts, or is the preimage used during the loop total junk (as one might expect during typical probing methods.

In the case that real attempts are made in a trial and loop fashion, how is the error to be returned determined in LND?

  • LND uses real preimages for each trial-and-error payment attempt in the context of pathfinding.
    – Mani T
    Aug 25, 2023 at 9:03
  • If a payment attempt fails, the real preimage is not revealed, and the funds are not claimed.
    – Mani T
    Aug 25, 2023 at 9:04


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