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blip-0034: the recommended_feerates message
Many lightning messages include feerates for on-chain transactions. Nodes receiving those messages are supposed to reject them if they are considered too low or too high. However, there is no mechanism to let peers know which feerates we currently find acceptable, which leads to frequent failures, especially when the mempool feerates fluctuate quickly. We introduce an optional message to advertise to our peers the feerates we'd like to use when funding new or existing channels.
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Diff for: ‎README.md

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For more detail on the process, please read [bLIP-0001](./blip-0001.md) and
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[bLIP-0002](./blip-0002.md).
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| Number | Title | Author | Status |
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|--------------------------|--------------------------------|-----------------------------|--------|
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| [1](./blip-0001.md) | bLIP Process | Ryan Gentry | Active |
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| [2](./blip-0002.md) | Reserved Values | Bastien Teinturier | Active |
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| [3](./blip-0003.md) | Keysend | Valentine Wallace | Active |
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| [10](./blip-0010.md) | Podcasting 2.0 | Satoshis Stream | Active |
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| [11](./blip-0011.md) | NameDesc | Hampus Sjöberg | Active |
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| [17](./blip-0017.md) | Hosted Channels | Anton Kumaigorodskiy | Active |
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| [25](./blip-0025.md) | Forward less than onion value | Valentine Wallace | Active |
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| [32](./blip-0032.md) | Onion Message DNS Resolution | Matt Corallo | Active |
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| Number | Title | Author | Status |
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|--------------------------|------------------------------------|-----------------------------|--------|
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| [1](./blip-0001.md) | bLIP Process | Ryan Gentry | Active |
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| [2](./blip-0002.md) | Reserved Values | Bastien Teinturier | Active |
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| [3](./blip-0003.md) | Keysend | Valentine Wallace | Active |
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| [10](./blip-0010.md) | Podcasting 2.0 | Satoshis Stream | Active |
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| [11](./blip-0011.md) | NameDesc | Hampus Sjöberg | Active |
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| [17](./blip-0017.md) | Hosted Channels | Anton Kumaigorodskiy | Active |
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| [25](./blip-0025.md) | Forward less than onion value | Valentine Wallace | Active |
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| [32](./blip-0032.md) | Onion Message DNS Resolution | Matt Corallo | Active |
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| [34](./blip-0034.md) | The `recommended_feerates` message | Bastien Teinturier | Active |

Diff for: ‎blip-0002.md

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| Type | Name | Link |
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| ------- | ------------------------------- | -------------------------- |
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| 39409 | `recommended_feerates` | [bLIP 34](./blip-0034.md) |
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| 65535 | `invoke_hosted_channel` | [bLIP 17](./blip-0017.md) |
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| 65533 | `init_hosted_channel` | [bLIP 17](./blip-0017.md) |
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| 65531 | `last_cross_signed_state` | [bLIP 17](./blip-0017.md) |

Diff for: ‎blip-0034.md

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```
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bLIP: 34
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Title: The `recommended_feerates` message
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Status: Active
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Author: Bastien Teinturier <[email protected]>
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Created: 2024-07-02
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License: CC0
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```
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## Abstract
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Many lightning messages include feerates for on-chain transactions. Nodes
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receiving those messages are supposed to reject them if they are considered
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too low or too high. However, there is no mechanism to let peers know which
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feerates we currently find acceptable, which leads to frequent failures,
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especially when the mempool feerates fluctuate quickly.
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We introduce an optional message to advertise to our peers the feerates we'd
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like to use when funding new or existing channels.
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## Copyright
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This bLIP is licensed under the CC0 license.
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## Motivation
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This feature is particularly useful when mobile wallets initiate channel
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operations with their service provider: in most cases, they should use what
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the service provider recommends since they don't have access to a full node
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and the service provider would reject unacceptable feerates anyway.
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## Specification
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### The `recommended_feerates` message
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1. type: 39409 (`recommended_feerates`)
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2. data:
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* [`chain_hash`:`chain_hash`]
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* [`u32`:`funding_feerate_per_kw`]
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* [`u32`:`commitment_feerate_per_kw`]
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1. `tlv_stream`: `recommended_feerates_tlvs`
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2. types:
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1. type: 1 (`funding_feerate_range`)
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2. data:
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* [`u32`:`min_funding_feerate_per_kw`]
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* [`u32`:`max_funding_feerate_per_kw`]
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1. type: 3 (`commitment_feerate_range`)
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2. data:
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* [`u32`:`min_commitment_feerate_per_kw`]
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* [`u32`:`max_commitment_feerate_per_kw`]
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### Requirements
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The sender:
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* SHOULD frequently send `recommended_feerates` with feerates it currently
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accepts for channel funding operations.
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* SHOULD set `funding_feerate_per_kw` to the feerate it uses for funding
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channels.
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* SHOULD set `funding_feerate_range` to the range of acceptables feerates
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for funding channels.
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* SHOULD set `commitment_feerate_per_kw` to the feerate it uses for channel
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commitment transactions.
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* SHOULD set `commitment_feerate_range` to the range of acceptables feerates
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for channel commitment transactions.
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* SHOULD accept feerates that are inside the ranges it advertised.
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The receiver:
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* SHOULD not send `open_channel`, `open_channel2`, `splice_init`, `tx_init_rbf`
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or other channel funding messages using feerates that are outside of the
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advertised ranges.
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### Rationale
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While it won't guarantee success every time, taking into account our peer's
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recommended feerates reduces the frequency of failures when funding channels.
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### Test vectors
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The following test vectors describe how the `recommended_feerates` message is
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encoded:
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```json
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[
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{
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"recommended_feerates": {
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"chain": "testnet3",
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"funding_feerate_per_kw": "2500 sat/kw",
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"commitment_feerate_per_kw": "2500 sat/kw"
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},
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"encoded": "99f1 43497fd7f826957108f4a30fd9cec3aeba79972084e90ead01ea330900000000 000009c4 000009c4"
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},
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{
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"recommended_feerates": {
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"chain": "testnet3",
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"funding_feerate_per_kw": "5000 sat/kw",
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"commitment_feerate_per_kw": "253 sat/kw"
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},
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"encoded": "99f1 43497fd7f826957108f4a30fd9cec3aeba79972084e90ead01ea330900000000 00001388 000000fd"
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},
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{
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"recommended_feerates": {
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"chain": "testnet3",
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"funding_feerate_per_kw": "10000 sat/kw",
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"min_funding_feerate_per_kw": "5000 sat/kw",
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"max_funding_feerate_per_kw": "15000 sat/kw",
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"commitment_feerate_per_kw": "1000 sat/kw",
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"min_commitment_feerate_per_kw": "253 sat/kw",
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"max_commitment_feerate_per_kw": "2000 sat/kw"
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},
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"encoded": "99f1 43497fd7f826957108f4a30fd9cec3aeba79972084e90ead01ea330900000000 00002710 000003e8 01080000138800003a98 0308000000fd000007d0"
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}
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]
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```
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## Reference Implementations
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* eclair: <https://github.com/ACINQ/eclair/pull/2860>

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