Ability to set inbound and outbound fees

[Swissnode]

As a major channel balancer and node operator, it has become clear to me and the community of channel balancers I work with that we really need the ability to incentivize traffic in certain directions.

As such, we would highly recommend having inbound and outbound fees to allow such incentivization.

[Roasbeef]

As is, on the protocol level, you can only set the fees for outbound (routing an HTLC over that channel). The remote party controls the "inbound fees", since their bandwidth is used to carry the HTLC.

One thing we've discussed is possibly introducing "pair wise" fee schedules. So this would mean you can set different fees for A -> B, and A -> C, where B and C are your channels. We could possibly add some new TLV fields to the ChannelUpdate to make this possible, but no one has attempted to fully specify it yet.

[Swissnode]

Pairwise fees would be a GREAT option @Roasbeef ! Thanks for taking the time to look at this. I realise the discussion probably belonged on another repo, apologies if I hit the wrong one!!

Great work, loving Lightning and LND!

[Jestopher-BTC]

Either pairwise fees or inbound fees are gravely needed for node management! Inbound liquidity is a scarce resource and it does not have the same value even in different channels; some inbound is worth more in certain channels than others.

[grnqrtr]

Just adding that I agree. Having some kind of "pair wise" fees or inbound fees would be really helpful.

[Roasbeef]

This is a spec level thing, so closing here as the discussion needs to be started on the rfc repo and/or the dev mailing list.

[AbelLykens]

Opened in RFC repo:
lightning/bolts#835
Link added for reference. Mentioned you @Swissnode as original.

[joostjager]

But is this a spec level thing? It seems to me that this can also be a implementation-specific extension when inbound fees are always negative or zero. Ref: https://lists.linuxfoundation.org/pipermail/lightning-dev/2022-July/003643.html

[Roasbeef]

Re-opening since #6703 is now a thing