Measuring minrelaytxfee across the Bitcoin network

A detailed examination, leveraging a modified version of virtu’s p2p-crawler, focused on recording these messages from nodes that accept inbound connections. This study revealed that a vast majority of nodes, around 89% in the first scan and slightly less at 86.5% in the second scan, advertised a minimum relay fee of 1000 satoshis. However, a notable fraction of nodes did not broadcast a FEEFILTER message, suggesting potential operational nuances or the presence of spy nodes within the network, as theorized by Peter Todd. This phenomenon was particularly pronounced among IPv4 nodes.

Further investigation into the network unearthed a subset of nodes displaying an anomalously high minimum relay fee of 9170997 satoshis. To verify this anomaly, checks were conducted using Bitcoin Core to ensure accurate parsing by the crawler. The origin of this specific fee rate points to the Bitcoin Core's mechanism of rounding feerate filters for privacy reasons, as outlined in the FeeFilterRounder component. This component is designed to prevent node fingerprinting by adjusting the exact feefilter based on mempool contents, with MAX_FILTER_FEERATE set to 1e7, thereby rounding to 9170997.

Additionally, the research highlighted nodes operating on outdated software versions, lacking the capability to send FEEFILTER messages—a feature introduced in a 2016 GitHub pull request. Some nodes might also intentionally disable this function via a -feefilter configuration option available in versions post-2021, as indicated in another GitHub pull request. This intentional disabling could be motivated by various factors, including privacy concerns or specific operational strategies within the Bitcoin network.

The exploration provided nuanced insights across different network types (i2p, IPv4, IPv6, onion_v3), with i2p and onion_v3 networks demonstrating higher compliance with the 1000 satoshi minimum fee. In contrast, IPv4 and IPv6 networks exhibited a greater propensity for not sending FEEFILTER messages. These findings underline the diversity and complexity inherent in the network's structure and operation, prompting further discussions and investigations into the dynamics of node behavior and network policies in the decentralized ecosystem of Bitcoin. The collaborative nature of the cryptocurrency community played a crucial role in driving this research, highlighting the importance of shared knowledge and inquiry in understanding blockchain networks' intricacies.