[Lightning-dev] Hold fees: 402 Payment Required for Lightning itself

[Joost Jager]

Hi Bastien,

We add a forward upfront payment of 1 msat (fixed) that is paid
> unconditionally when offering an HTLC.
> We add a backwards upfront payment of `hold_fees` that is paid when
> receiving an HTLC, but refunded
> if the HTLC is settled before the `hold_grace_period` ends (see footnotes
> about this).
>

It is interesting that the forward and backward payments are relatively
independent of each other. In particular the forward anti-spam payment
could quite easily be implemented to help protect the network. As you said,
just transfer that fixed fee for every `update_add_htlc` message from the
offerer to the receiver.

I am wondering though what the values for the fwd and bwd fees should be. I
agree with ZmnSCPxj that 1 msat for the fwd is probably not going to be
enough.

Maybe a way to approach it is this: suppose routing nodes are able to make
5% per year on their committed capital. An aggressive routing node could be
willing to spend up to that amount to take down a competitor.

Suppose the network consists only of 1 BTC, 483 slot channels. What should
the fwd and bwd fees be so that even an attacked routing node will still
earn that 5% (not through forwarding fees, but through hold fees) in both
the controlled and the uncontrolled spam scenario?

- Joost
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