Port 30303 (Ethereum P2P)

Ethereum execution clients' (Geth, Nethermind) peer discovery and sync.

Registered (user) port, 1024-49151 TCPUDP Peer-to-peer Meant to face the internet

What port 30303 is used for

Ethereum execution clients' (Geth, Nethermind) peer discovery and sync.

Meant to face the internet. Fine to expose; keep JSON-RPC (8545) and the engine API (8551) private.

Port 30303 is in the registered range and has no IANA assignment. The usage above is unofficial but widespread.

Linux: is anything listening on TCP 30303?

sudo ss -tlnp 'sport = :30303'

Linux: UDP 30303

sudo ss -ulnp 'sport = :30303'

Linux / macOS: which process owns the port

sudo lsof -nP -i :30303

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':30303 '

Windows (Command Prompt)

netstat -ano | findstr :30303

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 30303 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 30303

From Windows

Test-NetConnection HOST -Port 30303

UDP probe (no reply does not prove it is closed)

nc -vzu -w 5 HOST 30303

ufw

sudo ufw allow 30303/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 30303 -j ACCEPT

nftables

sudo nft add rule inet filter input tcp dport 30303 accept

Windows Firewall

New-NetFirewallRule -DisplayName 'Allow TCP 30303' -Direction Inbound -Protocol TCP -LocalPort 30303 -Action Allow

ufw

sudo ufw allow 30303/udp

iptables

sudo iptables -A INPUT -p udp --dport 30303 -j ACCEPT

nftables

sudo nft add rule inet filter input udp dport 30303 accept

Windows Firewall

New-NetFirewallRule -DisplayName 'Allow UDP 30303' -Direction Inbound -Protocol UDP -LocalPort 30303 -Action Allow

All port numbers · Open port checker
Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.