Measuring minrelaytxfee across the Bitcoin network

Protocol Design
3

Thanks for sharing!

Bitcoin Core “rounds” the feerate filters a bit (i.e. it put them into bins) as sending an exact feefilter based on mempool contents is a way of fingerprinting nodes across networks. See FeeFilterRounder in src/policy/fees.h. The FeeFilterRounder defines a MAX_FILTER_FEERATE of 1e7 (10,000,000). 1e7 happens to “round” to 9170997. This can also be seen in this test where MAX_MONEY (21,000,000 * COIN) is “rounded” to 9170997.

When in IBD, a feefilter of MAX_MONEY is set:

so they should return a feefilter of 9170997. Maybe the nodes were in IBD when you connected to them?

Looking at some logs I can see the following pattern happening repeatedly:

We connect to peer=5129 at height 908087, the peer is at height 907929 (158 blocks behind). Initially, the peer sends a feefilter of 9170997. After four seconds, the peer lowers its feefilter of 9170997 to 1000.

2025-09-01T09:29:34.83Z [net] send version message: version 70016, blocks=908087, txrelay=1, peer=5129
2025-09-01T09:29:34.83Z [net] receive version message: version 70016, blocks=907929, txrelay=1, peer=5129
..
2025-09-01T09:29:35.99Z [net] received: feefilter of 0.09170997 BTC/kvB from peer=5129
2025-09-01T09:29:39.08Z [net] received: feefilter of 0.00001000 BTC/kvB from peer=5129

The code for is:

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