Measuring minrelaytxfee across the Bitcoin network

The focus was on reachable nodes and their FEEFILTER messages, particularly those accepting inbound connections. Throughout this study, conducted with scans on the 10th and 15th of September, a significant majority of nodes were found to advertise a minimum relay fee of 1000 satoshis. However, an interesting observation was the absence of FEEFILTER messages from a considerable portion of nodes, especially among IPv4 networks, where a higher rate of non-compliance was noted, suggesting potential operational peculiarities or the presence of spy nodes, as indicated by Peter Todd.

Further analysis revealed that a small fraction of nodes advertised unusually high minimum relay fees of 9170997 satoshis, a figure that piqued curiosity due to its specificity and significant deviation from the norm. This anomaly was meticulously verified for accuracy using Bitcoin Core, leading to an in-depth investigation into how Bitcoin Core manages minfeefilter values. It was discovered that Bitcoin Core employs a FeeFilterRounder mechanism to optimize feerate filters, intentionally adjusting them to prevent node fingerprinting. This adjustment results in certain nodes displaying the 9170997 feefilter value, particularly when in the Initial Block Download (IBD) phase, highlighting the dynamic nature of feefilters within the protocol and the intricate balance between privacy, security, and efficiency in the network's operations.

The examination also touched upon the software versions run by nodes, revealing that many of the nodes failing to send FEEFILTER messages were operating on software predating a critical 2016 update which introduced feefilter capabilities. Additionally, some nodes might have intentionally disabled the feefilter option through configurations available in software versions older than 2021. Interestingly, a considerable number of nodes not returning a feefilter were found to be using recent Core 27.x versions, contradicting initial assumptions about technological constraints. This prompted further scrutiny, uncovering that many such nodes were in the IBD phase at the time of connection, affecting their ability to process or respond to feefilter requests as expected.

These findings underscore the complexity and heterogeneity within the Bitcoin network and raise intriguing questions about node configurations, operational intentions, and the broader implications for network dynamics and behavior. The research highlights the value of collaborative inquiry and shared knowledge in the cryptocurrency community, contributing to a deeper understanding of the decentralized ecosystem’s intricacies.