Channel operation and payment forwarding

While a channel is open, the two nodes keep adding and removing HTLCs and signing new commitments: that is payment forwarding. Sooner or later, a channel ends.

Cooperative close

Both nodes agree on the final balance and sign one new closing transaction that pays each side directly. There are no time locks, the fee is small and agreed, and both get their money as soon as it confirms. This is how a channel should end.

⚡Close a channel cooperatively

CLI

NodeAlice · LNDBob · c-lightningChan · c-lightningDina · LNDNo node

BOB=$(JIFUNZE_NODE=bob lightning-cli getinfo | jq -r .id) POINT=$(lncli listchannels | jq -r --arg b "$BOB" '.channels[] | select(.remote_pubkey==$b) | .channel_point' | head -1) echo "Closing $POINT" lncli closechannel --chan_point "$POINT" bitcoin-cli -generate 6

▶ RunCheckReset lessonRestore starter code

These exercises need a laptop with the lab running. You can read the lesson on your phone.

Force close

If the other side is offline, unresponsive or misbehaving, a node can force close: it publishes its latest commitment transaction on its own. Then:

• the other side is paid immediately,
• the publisher's own output waits behind its time lock (blocks_til_maturity), and
• any HTLCs still in flight are settled on-chain, each with its own deadline.

⚡Force-close and watch the timelock

CLI

NodeAlice · LNDBob · c-lightningChan · c-lightningDina · LNDNo node

CHAN=$(JIFUNZE_NODE=chan lightning-cli getinfo | jq -r .id) POINT=$(lncli listchannels | jq -r --arg c "$CHAN" '.channels[] | select(.remote_pubkey==$c) | .channel_point' | head -1) lncli closechannel --force --chan_point "$POINT" bitcoin-cli -generate 1 sleep 3 lncli pendingchannels | jq '.pending_force_closing_channels[] | {blocks_til_maturity, limbo_balance}'

▶ RunCheckReset lessonRestore starter code

These exercises need a laptop with the lab running. You can read the lesson on your phone.

Dina's funds now show as limbo_balance with a count of blocks to go. On regtest you can mine them away; on mainnet that wait could be a day or more.