Description
LND version 0.18 which was released on May 30, 2024 included support for negative inbound routing fees. This feature allows routing node operators to offer a discount for traffic that comes in through specific channels.
Background information:
- https://www.mail-archive.com/[email protected]/msg02895.html
- htlcswitch: add inbound routing fees receive support lightningnetwork/lnd#6703
- routing: inbound fees send support lightningnetwork/lnd#6934
Now that almost a year has passed since, it seems that there is some uptake of the feature by node operators. LDK ignores negative inbound fees and therefore senders using LDK are potentially overpaying.
To address just that, LDK would only need to get send support. Receive support is exclusively relevant to routing nodes.
Additionally, it is worth considering extending the rapid gossip sync protocol to become more flexible with regards to extra channel update parameters - for inbound fees and also for what else might be added going forward.
In the network, there are currently (Feb 2025) around 2000 channel ends for which the node on that end advertizes a non-zero inbound fee. For a list of those nodes and the number of inbound fee channels per node, see Inbound fees analysis - nodes.csv
For 95% of the channels, the base fee is set to zero with just a proportional inbound fee set. The proportional inbound fee distribution (non-zero, down to -20 basis points) is shown here:
