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I suspect this depends heavily on the implementation, but maybe someone can shed light on the circumstances that would lead an implementation to force close a channel automatically.

A user asked this on stacker.news but I know all the wizards are on here.

Nobody in the right mind will force close a channel manually, without a reason. We all do that cooperative close, if a peer is still online and we really need to close that channel.

But automated force closing are really frustrating.

Let's make a list here of all situations, considerations, reasons, causes etc that a channel will be automatically force close and also if you know what steps to do to avoid them.

We have many LND nodes with this situation, few CLN and even fewer Eclair nodes. Possible causes:

  • some incompatibility between LN implementations ?
  • different CLTV delta settings between peers?
  • too many HTLC on the fly for long time?
  • a minimum time a node can be offline?
  • too many commit changes for a channel in a certain time?
  • bad reconnectivity?

1 Answer 1

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Answering from the perspective of the node that triggers the force-close:

  1. Outgoing HTLC times out (i.e., peer doesn't settle/fail in time, which can happen if the peer is offline/unreachable)
    1. There are plenty of special cases, including bugs, though. One fun example: on a payment A-B-C-... where I'm A, node C drops dead. The HTLC between B and C times out, B force-closes. The force-close transaction doesn't confirm in time (because B doesn't bump the fees), so the HTLC between A and B also runs into a time out and A force-closes the channel.
  2. Bugs like https://github.com/ElementsProject/lightning/issues/4649
  3. Incoming HTLC times out (I don't know the specifics, but I've seen force-closes where my peer's force-close transaction contained an HTLC that my force-close transaction doesn't have)
  4. Peer asks for force-close (recovery mode, "hey, I lost my channel state, please be so kind and broadcast your most recent force-close tx, kthxbye")
  5. Trivial: You trigger the force-close manually

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