<p>As far as I understand this is not needed. Let us assume we have an congested mempool and someone publishes an old channel state. This transaction will not be mined directly as the mempool is congested. The timelock during which this transaction can be revoked via the penalty mechanism is a relative one and starts as soon as the transaction is mined. So, this would happen once the fees are down again and then one can use the fees in their breach remedy transaction. </p>

<p>That being said, on-chain fees are a challenge for lightning. While a collaborative channel close can take the current state of the mempool into consideration and adjust the fees so that the channel closes quickly the case of of a unilateral close is much more difficult. When negotiating a new channel state, we don't know what the fees will be in the future. So, when force closing we might have over or underpaid but we can't change the fees anymore since this would require a signature from the unresponsive party.</p>

CC BY-SA 4.0
2019-02-21T04:40:30.890Z
It's well known that some mining pools are selling so-called "tx accelerators" - which is actually "bribe me with some additional tx fees". Therfore, even if the penalty tx may have a higher tx fee rate, it's still possible that the cheating tx got confirmed much earlier than the penalty tx
Chris Chen
CC BY-SA 4.0
2019-02-21T09:29:39.720Z
that is not a problem! The penalty tx is a tx that spends an output in the cheating tx within a timelock. so there is no chance to mine the penalty tx before the cheating tx got confirmed
Rene Pickhardt
CC BY-SA 4.0
2019-02-21T10:26:43.863Z
But it's still possible that the cheater finally extracts funds from expired relative-timelocked output, meanwhile the penalty tx is still stuck in the mempool due to insufficient fee rate.
Chris Chen
CC BY-SA 4.0
2019-02-21T12:18:33.917Z
Not really as you can set the fees for the penalty tx when pushing it. Since you get all the funds of the channel as a reward you should have quite some liquidity to set the highest fee rates.
Rene Pickhardt
CC BY-SA 4.0
2019-02-21T12:55:58.743Z
It doesn't seem a matter of fee rate only. Currently LN is still in very early stage - what if LN is adopted much wider in the future?
Chris Chen
CC BY-SA 4.0
2019-02-23T18:18:09.923Z
I think this answer understates the severity of the problem.  A worst-case scenario for LN (described in its original paper) is that heavy centralization results in a giant hub; the hub closes all of its channels in a cheating state; users of those channels try to broadcast remedy (justice) transactions, but there's not enough block space for all of them so, no matter how high fees go, it's certain some honest users will lose money (although they can use a scorched-earth policy to prevent the cheating hub from profiting).  The solution here is longer timeouts and advertising of scorch policies
David A. Harding
CC BY-SA 4.0
2019-03-06T07:09:38.783Z
The users won't care whether the cheating hub can profit. They only care about security of their own funds. If "scorched-earth policy" means "sacrifice my own money to enforce justice", I think most users won't accept it.
Chris Chen
CC BY-SA 4.0
2019-03-27T02:28:06.940Z
Here comes another problem - what if the mempool will never clear again in the future? If a user wants to force-close a channel, the only solution might be buying queue-cutting service (aka "tx accelerator") from miners.
Chris Chen
CC BY-SA 4.0
2019-02-20T07:18:20.260Z
2019-04-28T18:10:32.023Z
2019-04-28T18:10:32.023Z
Rene Pickhardt
<p>According to LN <a href="https://lightning.network/lightning-network-presentation-sfbitcoinsocial-2015-05-26.pdf" rel="nofollow noreferrer">social slides</a>, a fee market (in other word: "congested mempool", to my understanding) is good. But, there's systemic risks around penalty mechanism, so some sort of on-chain scaling (which looks like an emergency lane to my understanding) is still needed to mitigate them.</p>

<security><lightning-network><blockspace-market><risk-mitigation><ln-closing-channels>
Does LN require an on-chain "emergency lane" to mitigate systemic risks?
Chris Chen
# Does LN require an on-chain "emergency lane" to mitigate systemic risks?

(Asked by: username_0 on 2019-02-20)

According to LN [social slides](https://lightning.network/lightning-network-presentation-sfbitcoinsocial-2015-05-26.pdf), a fee market (in other word: "congested mempool", to my understanding) is good. But, there's systemic risks around penalty mechanism, so some sort of on-chain scaling (which looks like an emergency lane to my understanding) is still needed to mitigate them.

**Tags:** security, lightning-network, blockspace-market, risk-mitigation, ln-closing-channels


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## 1 answers

### Answer by username_1 on 2019-02-20. Score: 4

As far as I understand this is not needed. Let us assume we have an congested mempool and someone publishes an old channel state. This transaction will not be mined directly as the mempool is congested. The timelock during which this transaction can be revoked via the penalty mechanism is a relative one and starts as soon as the transaction is mined. So, this would happen once the fees are down again and then one can use the fees in their breach remedy transaction.

That being said, on-chain fees are a challenge for lightning. While a collaborative channel close can take the current state of the mempool into consideration and adjust the fees so that the channel closes quickly the case of of a unilateral close is much more difficult. When negotiating a new channel state, we don't know what the fees will be in the future. So, when force closing we might have over or underpaid but we can't change the fees anymore since this would require a signature from the unresponsive party.

> **Comments:**
> **username_0**: It's well known that some mining pools are selling so-called "tx accelerators" - which is actually "bribe me with some additional tx fees". Therfore, even if the penalty tx may have a higher tx fee rate, it's still possible that the cheating tx got confirmed much earlier than the penalty tx  
> **username_1**: that is not a problem! The penalty tx is a tx that spends an output in the cheating tx within a timelock. so there is no chance to mine the penalty tx before the cheating tx got confirmed  
> **username_0**: But it's still possible that the cheater finally extracts funds from expired relative-timelocked output, meanwhile the penalty tx is still stuck in the mempool due to insufficient fee rate.  
> **username_1**: Not really as you can set the fees for the penalty tx when pushing it. Since you get all the funds of the channel as a reward you should have quite some liquidity to set the highest fee rates.  
> **username_0**: It doesn't seem a matter of fee rate only. Currently LN is still in very early stage - what if LN is adopted much wider in the future?  
> **username_2**: I think this answer understates the severity of the problem.  A worst-case scenario for LN (described in its original paper) is that heavy centralization results in a giant hub; the hub closes all of its channels in a cheating state; users of those channels try to broadcast remedy (justice) transactions, but there's not enough block space for all of them so, no matter how high fees go, it's certain some honest users will lose money (although they can use a scorched-earth policy to prevent the cheating hub from profiting).  The solution here is longer timeouts and advertising of scorch policies  
> **username_0**: The users won't care whether the cheating hub can profit. They only care about security of their own funds. If "scorched-earth policy" means "sacrifice my own money to enforce justice", I think most users won't accept it.  
> **username_0**: Here comes another problem - what if the mempool will never clear again in the future? If a user wants to force-close a channel, the only solution might be buying queue-cutting service (aka "tx accelerator") from miners.  

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