124th peer connection closed every second #33267

1. 
   lnxsrt commented at 12:54 pm on August 28, 2025: none

   Is there an existing issue for this?

   • I have searched the existing issues

   Current behaviour

   I’m on Bitcoin Core v29.0.0

   I noticed that when at the max number of peers (124 total; 10 outbound; 114 inbound) the most recent peer connection is continually dropped after 1 second and another peer is selected. I can’t imagine this is good behavior for the network.

   As you can see, my peer count is very high (basically == number of seconds I’ve been at 124 peers) and the most recent peer only ever has an age of 1s.

   Expected behaviour

   I would expect the program to stop accepting connections when peers == max_peers, instead of accepting the connection and dropping it 1 second later.

   Steps to reproduce

   Leave client running on a high speed network long enough to hit 124 peers.

   Relevant log output

   No response

   How did you obtain Bitcoin Core

   Pre-built binaries

   What version of Bitcoin Core are you using?

   v29.0.0

   Operating system and version

   FreeBSD 14.3

   Machine specifications

   No response

2. 
   0xB10C commented at 1:37 pm on August 28, 2025: contributor

   This is likely normal behavior and not a bug. What you are seeing is Bitcoin Core’s inbound connection eviction in action. When a new inbound connection comes in, another connection may be closed in favor of it. This avoids an attacker filling all of your inbound connections in an attempt to eclipse you from the network. The inbound eviction algorithm takes care to protect certain peers from being disconnected - you can find details here.

   the most recent peer connection is continually dropped after 1 second and another peer is selected. I can’t imagine this is good behavior for the network.

   The connection that’s repeatedly dropped is probably an inbound connection from a network group (a /16 IP address range) with many existing inbound connections to you.

   https://github.com/bitcoin/bitcoin/blob/6ca6f3b37b992591726bd13b494369bee3bd6468/src/node/eviction.cpp#L238-L239

   As you can see, my peer count is very high

   Given you have already seen 3.2M peers, there’s probably someone frequently reconnecting to your node from the same network group(s). Based on what I see at my nodes, my guess is that this is related to LinkingLion. If the IP addresses match, you could consider banning the related subnets to avoid these connections.

3. maflcko added the label Questions and Help on Aug 28, 2025
4. maflcko added the label P2P on Aug 28, 2025
5. maflcko closed this on Aug 28, 2025

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