P2p_networking

Chapter 23: Peer-to-Peer Networking

Overview

Blockchain nodes communicate through Peer-to-Peer (P2P) networks. Understanding P2P networking is essential for node operators.

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23.1 P2P Network Basics

How Blockchain P2P Works

┌─────────────────────────────────────────────────────────────────┐
│                    P2P NETWORK OVERVIEW                          │
├─────────────────────────────────────────────────────────────────┤
│                                                                  │
│   Each node connects to multiple peers                            │
│                                                                  │
│       Node A                                                     │
│      / | | \                                                    │
│     /  | |  \                                                   │
│    /   | |   \                                                  │
│   B    C  D   E                                                │
│                                                                  │
│   Transactions flow: A → B, C, D, E                             │
│   Blocks propagate:  A → B → C → D → E                         │
│                                                                  │
│   No central server - fully decentralized                        │
│                                                                  │
└─────────────────────────────────────────────────────────────────┘

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23.2 Node Discovery

Discovery Methods

Method	Description
Bootnodes	Well-known nodes for initial connection
DNS Discovery	DNS-based peer discovery
DiscV5	Ethereum’s new discovery protocol
Kademlia	DHT-based peer discovery

Bootnodes in Ethereum

# Mainnet bootnodes
enr:-KG4QOtcL...@bootnode.mainnet.ethdisco.net:30303

# Connect to specific peers
geth --bootnodes "enr:-KG4..."

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23.3 Network Ports

Common Ports

Protocol	Port	Description
TCP P2P	30303	Ethereum mainnet
UDP Discovery	30303	Peer discovery
HTTP RPC	8545	JSON-RPC
WebSocket	8546	WS API

Firewall Configuration

# Allow P2P
sudo ufw allow 30303/tcp
sudo ufw allow 30303/udp

# Allow RPC (restrict to your IP)
sudo ufw allow from YOUR_IP to any port 8545

# Allow WebSocket
sudo ufw allow 8546/tcp

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23.4 Peer Management

Connecting to Peers

# In Geth console
admin.peers()           # List all peers
admin.addPeer("enr:...")  # Add specific peer

# Check peer count
net.peerCount

Static Peers

# config.toml
[Node]
StaticNodes = ["enr:...", "enr:..."]

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23.5 Network Troubleshooting

Common Issues

Issue	Cause	Solution
No peers	Firewall, network	Check ports, add bootnodes
Peer drops	Network issues	Check connectivity
Sync stuck	Peer issues	Try different peers

Debug Commands

# Check network info
curl http://localhost:8545 -X POST -H "Content-Type: application/json" \
  -d '{"jsonrpc":"2.0","method":"net_peerCount","params":[],"id":1}'

# Check enode
geth attach http://localhost:8545
admin.nodeInfo.enode

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Summary

• P2P networks enable decentralized communication
• Bootnodes help new nodes discover peers
• Proper firewall configuration is crucial
• Monitor peer count for network health

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Next Chapter

In Chapter 24: Node Discovery Protocols, we’ll explore discovery in detail.

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Last Updated: 2026-02-20