Ports

Chapter 25: Network Ports & Firewall Configuration

Overview

Proper firewall configuration is critical for blockchain node security and optimal network connectivity. This chapter provides comprehensive coverage of port management, firewall configuration, and network security best practices for blockchain nodes.

25.1 Common Ports for Blockchain Networks

Ethereum Ports

┌─────────────────────────────────────────────────────────────────────────────┐
│                        ETHEREUM NETWORK PORTS                                   │
├─────────────────────────────────────────────────────────────────────────────┤
│                                                                              │
│   P2P NETWORKING (Required for node operation)                               │
│   ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━                                      │
│                                                                              │
│   Port    Protocol   Purpose                    Access                      │
│   ━━━━    ━━━━━━━   ━━━━━━━━                  ━━━━━━                      │
│   30303   TCP/UDP   P2P networking            Public (0.0.0.0)           │
│   30303   UDP        Discovery (Discv5)        Public                      │
│                                                                              │
│   RPC & API PORTS                                                           │
│   ━━━━━━━━━━━━━━━                                                           │
│                                                                              │
│   Port    Protocol   Purpose                    Access                      │
│   ━━━━    ━━━━━━━   ━━━━━━━━                  ━━━━━━                      │
│   8545    TCP        HTTP JSON-RPC             Internal only               │
│   8546    TCP        WebSocket RPC             Internal only               │
│   8550    TCP        Engine API (Consensus)   Internal only               │
│   8551    TCP        Engine API (Auth)        Internal only               │
│                                                                              │
│   MONITORING PORTS                                                          │
│   ━━━━━━━━━━━━━━━━━                                                         │
│                                                                              │
│   Port    Protocol   Purpose                    Access                      │
│   ━━━━    ━━━━━━━   ━━━━━━━━                  ━━━━━━                      │
│   6060    TCP        Prometheus metrics        Internal                    │
│   6061    TCP        pprof debugging          Internal                    │
│   6062    TCP        p2p debugging            Internal                    │
│                                                                              │
└─────────────────────────────────────────────────────────────────────────────┘

Cosmos/Tendermint Ports

Port	Protocol	Purpose	Access
26656	TCP	P2P networking	Public
26657	TCP	RPC API	Internal
26660	TCP	Prometheus metrics	Internal
9090	TCP	gRPC	Internal
1317	TCP	REST API	Internal
26658	TCP	P2P metrics	Internal

Bitcoin Ports

Port	Protocol	Purpose	Access
8333	TCP	P2P networking (Mainnet)	Public
8332	TCP	RPC API (Mainnet)	Internal
18333	TCP	P2P networking (Testnet)	Public
18332	TCP	RPC API (Testnet)	Internal

Solana Ports

Port	Protocol	Purpose	Access
8000-10000	TCP	TPU (Transaction Processing)	Public
8900	TCP	RPC API	Internal
8901	TCP	WebSocket	Internal
7070	TCP	P2P networking	Public

25.2 Linux Firewall Configuration

UFW (Uncomplicated Firewall)

# Install UFW
sudo apt update
sudo apt install ufw

# View available applications
sudo ufw app list

# Default policies - SECURE
sudo ufw default deny incoming
sudo ufw default allow outgoing

# Allow SSH with rate limiting (prevents brute force)
sudo ufw limit 22/tcp comment 'SSH with rate limiting'

# Allow P2P networking (Ethereum)
sudo ufw allow 30303/tcp comment 'Ethereum P2P TCP'
sudo ufw allow 30303/udp comment 'Ethereum Discovery UDP'

# Allow RPC only from specific IP (replace with your IP)
sudo ufw allow from 10.0.0.0/8 to any port 8545 proto tcp comment 'RPC from private network'

# Allow Prometheus metrics (internal only)
sudo ufw allow from 127.0.0.1 to any port 6060 proto tcp comment 'Prometheus'

# Allow Grafana (if running on same host)
sudo ufw allow from 127.0.0.1 to any port 3000 proto tcp comment 'Grafana'

# View rules before enabling
sudo ufw show added

# Enable firewall
sudo ufw enable

# Check status
sudo ufw status verbose

iptables Rules

#!/bin/bash
# Flush existing rules
iptables -F
iptables -X

# Default policies
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT ACCEPT

# Allow loopback
iptables -A INPUT -i lo -j ACCEPT

# Allow established connections
iptables -A INPUT -m conntrack --ctstate ESTABLISHED,RELATED -j ACCEPT

# SSH with rate limiting
iptables -A INPUT -p tcp --dport 22 -m conntrack --ctstate NEW -m recent --set
iptables -A INPUT -p tcp --dport 22 -m conntrack --ctstate NEW -m recent --update --seconds 60 --hitcount 4 -j DROP
iptables -A INPUT -p tcp --dport 22 -j ACCEPT

# Ethereum P2P
iptables -A INPUT -p tcp --dport 30303 -j ACCEPT
iptables -A INPUT -p udp --dport 30303 -j ACCEPT

# RPC (internal network only)
iptables -A INPUT -p tcp --s 10.0.0.0/8 --dport 8545 -j ACCEPT

# Prometheus
iptables -A INPUT -p tcp --s 127.0.0.1 --dport 6060 -j ACCEPT

# Save rules
iptables-save > /etc/iptables/rules.v4

25.3 Cloud Provider Firewall Configuration

AWS Security Groups

┌─────────────────────────────────────────────────────────────────┐
│                    AWS SECURITY GROUP CONFIGURATION                  │
├─────────────────────────────────────────────────────────────────┤
│                                                                  │
│   INBOUND RULES:                                                  │
│   ━━━━━━━━━━━━━━                                                  │
│                                                                  │
│   Type        Protocol  Port    Source        Purpose            │
│   ━━━━        ━━━━━━━━  ━━━━━━  ━━━━━━━━      ━━━━━━━━         │
│   Custom TCP  TCP       30303   0.0.0.0/0    Ethereum P2P     │
│   Custom TCP  TCP       8545    10.0.0.0/16  RPC (private)    │
│   SSH         TCP       22      <YOUR_IP>     Admin access      │
│                                                                  │
│   OUTBOUND RULES:                                                 │
│   ━━━━━━━━━━━━━━                                                  │
│                                                                  │
│   Type        Protocol  Port    Destination   Purpose            │
│   ━━━━        ━━━━━━━━  ━━━━━━  ━━━━━━━━━━   ━━━━━━━━         │
│   All Traffic ALL      ALL     0.0.0.0/0    Default allow      │
│                                                                  │
│   BEST PRACTICES:                                                 │
│   ━━━━━━━━━━━━━━                                                  │
│   - Never open RPC to 0.0.0.0/0                                │
│   - Use specific IP ranges for access                            │
│   - Enable only required ports                                    │
│   - Use VPC for node isolation                                   │
│                                                                  │
└─────────────────────────────────────────────────────────────────┘

GCP Firewall

# Allow P2P from anywhere
gcloud compute firewall-rules create allow-ethereum-p2p \
    --description "Allow Ethereum P2P networking" \
    --allow tcp:30303,udp:30303 \
    --source-ranges 0.0.0.0/0 \
    --target-tags blockchain-node

# Allow RPC from internal network
gcloud compute firewall-rules allow-ethereum-rpc \
    --description "Allow Ethereum RPC from internal" \
    --allow tcp:8545 \
    --source-ranges 10.128.0.0/9 \
    --target-tags blockchain-node

# Allow SSH from specific IP
gcloud compute firewall-rules allow-ssh \
    --description "Allow SSH" \
    --allow tcp:22 \
    --source-ranges <YOUR_IP>/32 \
    --target-tags blockchain-node

Azure Network Security Groups

# Create NSG
az network nsg create \
  --resource-group myResourceGroup \
  --name blockchain-node-nsg

# Allow P2P
az network nsg rule create \
  --resource-group myResourceGroup \
  --nsg-name blockchain-node-nsg \
  --name allow-p2p \
  --protocol '*' \
  --direction Inbound \
  --source-address-prefix Internet \
  --destination-port-range 30303 \
  --access Allow

# Allow RPC from VNet
az network nsg rule create \
  --resource-group myResourceGroup \
  --nsg-name blockchain-node-nsg \
  --name allow-rpc \
  --protocol TCP \
  --direction Inbound \
  --source-address-prefix VirtualNetwork \
  --destination-port-range 8545 \
  --access Allow

25.4 Port Security Best Practices

Port Access Matrix

┌─────────────────────────────────────────────────────────────────┐
│                      PORT ACCESS MATRIX                             │
├─────────────────────────────────────────────────────────────────┤
│                                                                  │
│   Port     Public    Internal   Authentication    Encryption    │
│   ━━━━━    ━━━━━━    ━━━━━━━    ━━━━━━━━━━━━━    ━━━━━━━━━━   │
│   30303    ✅ Yes     ✅ Yes      None              None        │
│   8545      ❌ No      ✅ Yes      API Key          TLS Optional│
│   8546      ❌ No      ✅ Yes      API Key          WSS         │
│   6060      ❌ No      ✅ Yes      None              None        │
│   22        ❌ No      ❌ No       SSH Key + MFA     SSH         │
│                                                                  │
│   LEGEND:                                                        │
│   ✅ Yes - Required/Allowed                                       │
│   ❌ No - Not allowed                                            │
│                                                                  │
└─────────────────────────────────────────────────────────────────┘

Network Isolation

# Create isolated network namespace for node
sudo ip netns add blockchain-node

# Run node in isolated namespace
sudo ip netns exec blockchain-node geth [options]

# Or use Docker network isolation
docker network create --driver bridge blockchain-net

docker run -d \
  --name ethereum-node \
  --network blockchain-net \
  -p 30303:30303 \
  -p 30303:30303/udp \
  ethereum/client-go

25.5 Troubleshooting Port Issues

Common Issues and Solutions

Issue	Cause	Solution
P2P not connecting	Firewall blocking	Check ports 30303 TCP/UDP
RPC timeout	Wrong IP binding	Bind to 0.0.0.0 or correct IP
Discovery failing	UDP blocked	Enable UDP 30303
Metrics not exposed	Port not enabled	Enable —metrics flag

Testing Ports

# Check if port is listening
sudo netstat -tlnp | grep 8545
sudo ss -tlnp | grep 8545

# Test external connectivity
nc -zv <external-ip> 30303
telnet <external-ip> 8545

# Check firewall rules
sudo iptables -L -n | grep 8545
sudo ufw status | grep 8545

# Test from external location
curl http://<external-ip>:8545

25.6 Interview Questions

Question	Answer
Which ports need to be open for Ethereum P2P?	30303 TCP and UDP
How do you secure RPC access?	Bind to localhost, use firewall, enable TLS
What is the difference between P2P and RPC ports?	P2P is for node-to-node communication, RPC is for client applications
Why is UDP needed for Ethereum?	For node discovery (Discv5 protocol)
How do you restrict RPC to internal network?	Use firewall rules or bind to internal IP

Summary

Always use least-privilege principle for firewall rules
Never expose RPC ports to the public internet
Use cloud provider security groups for cloud deployments
Implement rate limiting for SSH to prevent brute force
Test port connectivity after configuration

Next Chapter

In Chapter 26: Node Bootstrap & Static Peers, we’ll explore node discovery and peer connections.

Last Updated: 2026-02-20