Port 8333 (Bitcoin P2P)

Bitcoin Core peer-to-peer network (8332 is the JSON-RPC port).

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

What port 8333 is used for

Bitcoin Core peer-to-peer network (8332 is the JSON-RPC port).

Meant to face the internet. Exposing the P2P port is fine for a full node; never expose RPC on 8332.

Port 8333 is in the registered range and has no IANA assignment. The usage above is unofficial but widespread.

Linux: is anything listening on TCP 8333?

sudo ss -tlnp 'sport = :8333'

Linux / macOS: which process owns the port

sudo lsof -nP -i :8333

Older Linux / BSD (net-tools)

sudo netstat -tlnp | grep ':8333 '

Windows (Command Prompt)

netstat -ano | findstr :8333

Windows (PowerShell)

Get-NetTCPConnection -LocalPort 8333 -State Listen | Select LocalAddress,OwningProcess

From another machine

nc -vz -w 5 HOST 8333

From Windows

Test-NetConnection HOST -Port 8333

ufw

sudo ufw allow 8333/tcp

iptables

sudo iptables -A INPUT -p tcp --dport 8333 -j ACCEPT

nftables

sudo nft add rule inet filter input tcp dport 8333 accept

Windows Firewall

New-NetFirewallRule -DisplayName 'Allow TCP 8333' -Direction Inbound -Protocol TCP -LocalPort 8333 -Action Allow

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Assignment data: IANA port number registry (public domain), retrieved 2026-11-10.