<p>There are no specific relay policy rules that apply to CPFP, because unlike RBF, CPFP is not a relay policy. It's a completely normal new, additional, transaction that gets relayed. The fee-bumping effect is not achieved by a special relay mechanism, but by the miner's block building mining logic recognizing the combination of child and parent as better than the parent alone.</p>
<p>For this to work, the block building code needs to be sufficiently powerful to recognize this. This is the case if the miner directly or indirectly uses Bitcoin Core (version 0.13.0 or later).</p>
<p>Note that there are general policy rules that apply to dependant transactions (e.g. the ancestor and descendant count limits, which are by default 25 transactions). They're not specific to CPFP, but may impact its use.</p>

CC BY-SA 4.0
2023-12-08T23:25:37.970Z
`e.g. the ancestor and descendant count limits, which are by default 25 transactions` So, every transaction has the ancestor and descendant count. 1) I know that descendant count includes the transaction itself, is this also the case with the ancestor count? 2) Is the limit per count 25 (25 for descendant count and 25 for ancestor count) or in total?
LeaBit
CC BY-SA 4.0
2023-12-08T23:30:36.463Z
Yes, ancestor count also includes the transaction itself. The limits are configurable, but as of Bitcoin 26.0 (and ever since these concepts were introduced), the defaults have been 25 and 25.
Pieter Wuille
CC BY-SA 4.0
2023-12-08T19:54:55.147Z
2023-12-08T19:54:55.147Z
Pieter Wuille
<p><a href="https://bitcoin.stackexchange.com/a/120774/145749">Here</a> <em>Murch</em> defined the rules related to <strong>RBF</strong>, as one of the techniques for fee bumping. He also posted a link to Bitcoin Core's official documentation related to the implementation of RBF (<a href="https://github.com/bitcoin/bitcoin/blob/master/doc/policy/mempool-replacements.md" rel="nofollow noreferrer">link</a>).</p>
<p>However, I am interested in what are all the rules for <strong>CPFP</strong> as another fee bumping technique? Posting just the official documentation, some documentation like <em>Murch</em> posted, (or some similar relevant material) would also be sufficient for me.</p>

<child-pays-for-parent>
What are all the rules related to CPFP fee bumping?
LeaBit
# What are all the rules related to CPFP fee bumping?

(Asked by: username_0 on 2023-12-08)

[Here](https://bitcoin.stackexchange.com/a/120774/145749) *Murch* defined the rules related to **RBF**, as one of the techniques for fee bumping. He also posted a link to Bitcoin Core's official documentation related to the implementation of RBF ([link](https://github.com/bitcoin/bitcoin/blob/master/doc/policy/mempool-replacements.md)).

However, I am interested in what are all the rules for **CPFP** as another fee bumping technique? Posting just the official documentation, some documentation like *Murch* posted, (or some similar relevant material) would also be sufficient for me.

**Tags:** child-pays-for-parent


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## 1 answers

### Answer by username_1 on 2023-12-08. Score: 5 | Accepted answer

There are no specific relay policy rules that apply to CPFP, because unlike RBF, CPFP is not a relay policy. It's a completely normal new, additional, transaction that gets relayed. The fee-bumping effect is not achieved by a special relay mechanism, but by the miner's block building mining logic recognizing the combination of child and parent as better than the parent alone.

For this to work, the block building code needs to be sufficiently powerful to recognize this. This is the case if the miner directly or indirectly uses Bitcoin Core (version 0.13.0 or later).

Note that there are general policy rules that apply to dependant transactions (e.g. the ancestor and descendant count limits, which are by default 25 transactions). They're not specific to CPFP, but may impact its use.

> **Comments:**
> **username_0**: `e.g. the ancestor and descendant count limits, which are by default 25 transactions` So, every transaction has the ancestor and descendant count. 1) I know that descendant count includes the transaction itself, is this also the case with the ancestor count? 2) Is the limit per count 25 (25 for descendant count and 25 for ancestor count) or in total?  
> **username_1**: Yes, ancestor count also includes the transaction itself. The limits are configurable, but as of Bitcoin 26.0 (and ever since these concepts were introduced), the defaults have been 25 and 25.  

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