fix: improve libp2p connection limits for network discovery

[jorem321]

Context

After the Aztec network underwent its migration to v2.0.2, we noticed an inability to obtain reliable stats from the P2P network via our libp2p crawler deployed on aztec.nethermind.io.

Further investigation (by reading DEBUG logs on Aztec nodes) revealed rejections of the crawler's connection with the following type of errors:

2025-09-24 17:29:09.371 error[17:29:09.352] DEBUG: p2p:libp2p_service:libp2p_service:libp2p:tcp:listener error: inbound connection failed

This led to investigation of yarn-project/p2p/src/services/libp2p/libp2p_service.ts, which manages the libp2p connection at the TCP/Noise layer.

We identified that the ConnectionManager was configured with maxConnections: maxPeerCount. This configuration is too strict, causing rejections of any type of connections once the peer is at maxPeerCount. Moreover, it is inconsistent with the behavior of e.g. Ethereum consensus clients, which keep a buffer for discovery, as shown in the table below.

Current Aztec Parameter	Role/Purpose	Lighthouse Equivalent	Prysm Equivalent	Teku Equivalent
connectionManager.maxConnections: maxPeerCount	Maximum total connections - Hard limit on concurrent peer connections to prevent resource exhaustion. libp2p docs	max_established: target_peers * 1.3 (30% buffer)	connManager high: max(MaxPeers + 32, 192) (92% buffer at MaxPeers=100)	TargetPeerRange.upperBound: 100 (fixed, no scaling)
connectionManager.minConnections: 0	Minimum connection target - Ensures node maintains baseline connectivity for network health. libp2p docs	No direct equivalent (discovery-based)	No direct equivalent (pruning threshold only)	TargetPeerRange.lowerBound: 64 (application-level minimum)
tcp.maxConnections: Math.ceil(maxPeerCount * 1.5)	Transport layer limit - Controls TCP connection acceptance before libp2p validation. libp2p source code	libp2p default: Infinity (no limit)	libp2p default: Infinity (no limit)	libp2p default: Infinity (no limit)
tcp.closeAbove: maxPeerCount * 2	Connection burst protection - Temporarily stops accepting new connections during traffic spikes. libp2p source code	libp2p default: Infinity (no limit)	libp2p default: Infinity (no limit)	libp2p default: Infinity (no limit)

In order to keep Aztec's P2P network in line with the standards outlined above, this PR reviews and amends key parameters in the libp2p_service.

Changes Made

• Set connectionManager.maxConnections: maxPeerCount * 2. Allows a more generous buffer for network discovery and crawling---consistent with Prysm's approach.
• Set connectionManager.minConnections: Math.floor(maxPeerCount * 0.5). The previous choice was zero, which disabled the functionality of libp2p dialing peers from the peer book when peer counts get low. It is recommended to bump this parameter to help keep peer counts up, like Teku does.
• Set tcp.maxConnections: maxPeerCount * 2. As per the libp2p docs, tweaking this parameter "will have no effect if it is larger than the value configured for the ConnectionManager maxConnections parameter", hence we set it equal.
• Set tcp.closeAbove : maxPeerCount * 3 (still an improvement over libp2p's Infinity default, offering burst protection at the lowest networking level.)

[AztecBot]

💚 All backports created successfully

Status	Branch	Result
✅	v2

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