If I change the fee in one of my channels, how long does it take for the update to get propagated through the network? Are there any rough estimates on how long until it reaches, say, 90% of the nodes?
If a node is directly connected to yours via a direct channel then they should be able to see any changes to the fees immediately upon attempting to route through this channel.
However if there is for example a node multiple hops outside of your channels, likely they would need to wait until a route happens through this specific path before they would be able to verify the fee rate you have set.
So if they are directly connected they can query the fee directly by doing channel re-balancing or something like that, if they are not directly connected they need to learn about the fee rate from multi-hop paths.
This is just from my experience though I'm sure there is a better technical answer.
1I thought that the p2p layer propagates fee updates somehow, even when no transactions are being routed. Otherwise, how can my node learn about the fees of all the channels in the network? Mar 15 at 2:34
This could be true, I don't want to say something incorrect technically I am just speaking from what I experienced while using lightning a little while back. If that is true what it means is that the nodes connected to your nodes still need to learn about the fees in-between their channels so they can technically constantly update everytime someone changes their fee rate but I suppose this also introduces a bandwith spam vector and thus probably has some limitation to it.– PoseidonMar 15 at 15:09
For example the lightning watchtowers that can see fees (since you set up a channel with them) probably do not update those fee rates in real time to prevent spam. And someone without access to a lightning watchtower or a channel connected to yours would likely not be able to (or need to) see/verify your fee rates. So in a sense I think it might be more accurate to ask how fast this fee rate propagates to 90% of ln nodes indirectly connected to yours which is not necessarily the entire lightning network. (question seems to imply entire network propagation)– PoseidonMar 15 at 15:13